Accepted in Journal of Atmospheric and Oceanic Technology Corresponding Author Address

2A review of research progress on CO capture,storage,and utilization in 34Q156789111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758596061626364656667686970717273747576with 58%of the sources being located within the east and south 77central regions.The contributions of large point sources in each 78sector to total CO 2emissions in China are listed in Fig.2[13].With 79rapid development of energy technologies in the 21st century,fos-80sil fuels,especially coal,will still remain the dominant energy0016-2361/$-see front matter Ó2011Elsevier Ltd.All rights reserved.doi:10.1016/j.fuel.2011.08.022⇑Corresponding authors.Q2Address:State Key Laboratory of Coal Conversion,Institute of Coal Chemistry,Chinese Academy of Sciences,Taiyuan 030001,China (Y.Sun).Tel.:+863514049612;fax:+863514041153.E-mail addresses:zhaoning@ (N.Zhao),weiwei@ (W.Wei),yhsun@ (Y.Sun).Please cite this article in press as:L Q1i L et al.A review of research progress on CO 2capture,storage,and utilization in Chinese Academy of Sciences.Fuel(2011),doi:10.1016/j.fuel.2011.08.022source in China for decades to come.Chinese government recognized the huge challenge of CO 2abatement while satisfying ever-increasing energy demand.In the light of this situation,November 26,2009,China officially announced action to control emissions per unit of GDP by 40–45%by 2020,based on 86levels [14].To address this,China is undertaking a range of techni-87cal research and development projects on CCSU,including the na-88tional fundamental research and high-tech programs,as well as a 89large number of international programs.The CCS projects,fun-90dings,and research institutes in China is shown in Table 1.91Since 1990,China had carried out a series of climate change 92projects under framework of national programs,such as China’s 93National Climate Change Program (CNCCP),National Hi-tech R&D949596979899100101102103104105106107108109110111112113114115116117118119120121cooperation with international on CCSU.On the basis of the finical 122support of both Chinese government and CAS,a lot of progresses 123were obtained in several academic institutes in CAS including 124CO 2capture;enhanced oil recovery (EOR)and enhanced coal bed 125methane (ECBM)projects as well as CO 2chemical utilizations.This 126brief review has covered the research progress in CO 2capture,stor-127age,and utilization in CAS.2.The contributions of large point sources in each sector to overall total emissions in China [12].Please cite this article in press as:L Q1i L et al.A review of research progress on CO 2capture,storage,and utilization in Chinese Academy of Sciences.Fuel(2011),doi:10.1016/j.fuel.2011.08.022128129130131132133134135136137aration,and cryogenic fractionation.138 2.1.Amine-based scrubbing solvent139Amine scrubbing is a well known technology for capturing CO 2140from flue gas,which has been widely deployed on a large scale 141across several industries [25–28].The industrially most important142143144145146147148149150151152the environment [30].1532.2.Ionic liquids154Therefore,a nonvolatile solvent that could facilitate CO 2capture 155without the loss of solvent into the gas stream would be advanta-156geous.Ionic liquids (ILs)are commonly defined as liquids whichTable 1CCS projects,fundings,and research institutes in China.China and international cooperation on CCS projects and fundingsResearch institutes aBNLMS–CAS IET–CAS RCEES–CAS ICC–CAS IPE–CAS LICP–CAS CIAC–CAS National High Technology Research and Development Program of China (863)SIC–CAS National Key Basic Research and Development Program of China (973)IGG–CAS China’s National Climate Change Program (CNCCP)IAP–CAS L.L Q1i et al./Fuel xxx (2011)xxx–xxx3Please cite this article in press as:L Q1i L et al.A review of research progress on CO 2capture,storage,and utilization in Chinese Academy of Sciences.Fuel(2011),doi:10.1016/j.fuel.2011.08.022157are composed entirely of ions with a melting point of less than 158100°C.ILs have many unique properties in comparison to other 159solvents as extremely low volatility,broad range of liquid temper-160ature,high thermal and chemical stability,and tunable physico-161chemical characteristics and as a result,ILs have been considered 162as a potential substitute of aqueous amine solutions for CO 2cap-163ture [31–34].164In Changchun Institute of Applied Chemistry,Chinese Academy 165of Sciences (CIAC–CAS),a novel dissolving process for chitin and 166chitosan was developed by using the ionic liquid 1-butyl-3-167methyl-imidazolium chloride ([Bmim]Cl)as a solvent for capturing 168and releasing CO 2.The results showed that the chitin/IL and chito-169170171172173174175176177178179180181182183184185186187188189190191192193194195196197198199200201tant to consider the maximum mass loading when considering the 202support of ILs on inert substrates –yes,these can enhance the ILs’203ability to take up CO 2,but at the expense of cycling an inert sorbent 204round a thermal cycle.The ILs are also monstrously expensive,the 205complex structure,and high cost for preparation,compared to sim-206pler solvents such as MEA or ammonia.Thus,the potential for 207improving CO 2solubilities and reducing cost of the ILs still needs 208to be studied for future applications.In 2010,in Beijing National 209Laboratory for Molecular,Chinese Academy of Sciences (BNLMS–210CAS),Zhang and co-workers first reported on CO 2capture by 211hydrocarbon surfactant liquids.It also found that CO 2had high sol-212ubility in low-cost hydrocarbon surfactant liquids,and the ab-213and the 214215216such as corrosion,at 217regenerable solid sor-218concept for CO 2recov-219into amine-based and 220221222with various so-223as silica gels,activated 224have been shown to phys-225enhance the sorp-226of many amine-based 227In Dalian Institute of 228(DICP–CAS),Zhang 229silica foam (MCF)materi-230with polyethyl-231The results showed that 232having large window 2333.45mmol CO 2/g sorbent 234In Institute of Coal Chem-235Zhao et al.studied 236materials derived 237sorption capabili-238°C and 1bar.The as-pre-239selectivity for CO 2over 240prepared a series of CO 2241pentamine (TEPA)was 242(PMHS)based mesopor-243The highest absorption 24475°C with the 10vol.%245was higher than most 246Desorption could 247in 1h [46].248of amine-based sorbent 249capacity of solid sorbent.250have poor mechanical 251amine-based sorbents 252and require signifi-253processes.254255sorbents for CO 2capture 256Alkali earth metal,such 257form alkali earth metal-258vapor at high tempera-259and post-combus-260simplified process flow 261the calcium looping 262vessel (the carbonator)4L.L Q1i et al./Fuel xxx (2011)xxx–xxxPlease cite this article in press as:L Q1i L et al.A review of research progress on CO 2capture,storage,and utilization in Chinese Academy of Sciences.Fuel(2011),doi:10.1016/j.fuel.2011.08.022the carbonation reaction between CO 2and solid CaO separates CO from coal-combustion flue gas at a temperature between 600°and 650°C.The CaCO 3formed is then passed to another vessel (the calciner),where it is heated to reverse the reaction (900–950°C),releasing the CO 2suitable for sequestration,and regener-ating the CaO-sorbent which is then return to the carbonator.The carbonation process is exothermic,which is matched with the temperature of a steam cycle,allowing recuperation of the heat.In IPE–CAS,the decomposition conditions of CaCO 3particles for CO 2capture in a steam dilution atmosphere (20–100%steam 307308309310311312313314315316317318319320321322323324325326327328329330332333334335336337338339340341342343344345346347348349350351352353354355Fig.3.The process flow diagram of post-combustion capture using the calcium looping cycle [47,48].Please cite this article in press as:L Q1i L et al.A review of research progress on CO 2capture,storage,and utilization in Chinese Academy of Sciences.Fuel(2011),doi:10.1016/j.fuel.2011.08.022strength (998N/cm 2)and exhibited good stability in multiple cy-cles [74,75].Furthermore,the application of a conceptual CO 2cap-ture process using this sorbent was proposed for an existing coal fired power plant [75].However,to optimize CO 2sorption capacity,understand of the interaction between CO 2and the sorbent need to be studied in the further work.Moreover,much work remains before the technology fluidized bed CO 2capture can be commercialized.Simulta-neously,the numerical simulation based on the computational fluid 365dynamics (CFD)method will become a research focus in the future.366 3.CO 2storage367Following the capture and transport process,CO 2can be dis-368posed of in natural sites such as deep geological sequestration,369mineral carbonation,or ocean storage [76].There are three geolog-370ical formations that have also been recognized as major potential 371CO 2sinks:deep saline-filled sedimentary (DSFs),depleted oil 372natural gas reservoirs,and unmineable coal-seams.The geology 373also suggests possibilities for CO 2enhanced oil recovery (CO 374EOR),CO 2enhanced gas recovery (CO 2–EGR)and CO 2enhanced 375coal-bed methane recovery (CO 2–ECBM)projects [12].3763.1.Geological sequestration377Geological storage involves injecting CO 2at depths greater than 3781000m into porous sedimentary formations using technologies 379derived from the oil and gas industry [77].CO 2can be stored in 380supercritical state at depth below 800–1000m,which provides 381the potential for efficient utilization of the space,due to the li-382quid-like density of supercritical CO 2.The point at which CO 2Table 2Performance summary of K-based sorbents capturing CO 2.Material Temperature (°C)CO 2partial pressure (bar)e Total capacity (mmol CO 2/g sorbent)Method f Regenerature temperature (°C)Ref.K 2CO 3/AC a 600.01 1.95TCD g 150[62]K 2CO 3/SiO 2600.010.23TCD g –[62]K 2CO 3/USY 600.010.43TCD g –[62]K 2CO 3/CsNaX 600.01 1.35TCD g –[62]K 2CO 3/Al 2O 3600.01 1.93TCD g 350[62]K 2CO 3/CaO 600.01 1.11TCD g –[62]K 2CO 3/MgO 600.01 2.70TCD g 400[62]K 2CO 3/TiO 2600.01 1.89TCD g 150[62]K 2CO 3/Al 2O 3600.01 1.96TCD g >300[63]Re-KAl(I)30b 600.01 1.86TCD g <200[63]g Fig.5.The schematic diagram of experimental apparatus for the fluidized bed [74,75].6L.L Q1i et al./Fuel xxx (2011)xxx–xxxPlease cite this article in press as:L Q1i L et al.A review of research progress on CO 2capture,storage,and utilization in Chinese Academy of Sciences.Fuel(2011),doi:10.1016/j.fuel.2011.08.022383transforms from critical to supercritical point is 31.1°C and 3847.38MPa [78].CO 2is injected usually in the supercritical form into 385the saline aquifer or depleted oil or gas reservoir.Four major clas-386ses of deep geologic reservoirs present within China have been 387identified and evaluated as candidates for the long-term storage 388of anthropogenic CO 2:deep saline-filled sedimentary (DSFs)for-389mations,depleted gas basins,depleted oil basins with potential 390for CO 2–EOR,and deep unmineable coal seams with potential for 391CO 2–ECBM.Fig.6shows the map of the combined location and ex-392tent of candidate geologic CO 2storage formations in China [13].393Because the CO 2industry is not mature,there are few active CO 2394storage projects which can provide site specific information;hence417China are also potential storage candidates.Recently,other re-418search has also focused on estimating the distance between CO 2419sources and potential sinks.Zheng et al.superimposed the loca-420tions of these 27facilities onto maps of sedimentary basins in each 421of the five regions of China (Huabei,Ordos,Dongbei,Yuwan,and 422Xinjiang).The majority of the candidate CO 2sources are found in 423the Ordos,Huabei and Dongbei regions [85].424The China–UK Near Zero Emissions Coal (NZEC)Initiative exam-425ined options for carbon (CO 2)capture,transport and geological 426storage in China,which was developed under the 2005EU–China 427NZEC Agreement that aims to demonstrate CCS in China and the 428EU [16,86–88].The NZEC Initiative has evaluated the potential to 429430431432433434435436437438439440441442443444445446447448449450451L.L Q1i et al./Fuel xxx (2011)xxx–xxx7Please cite this article in press as:L Q1i L et al.A review of research progress on CO 2capture,storage,and utilization in Chinese Academy of Sciences.Fuel(2011),doi:10.1016/j.fuel.2011.08.022452Kailuan mining area (Hebei Province)and deep saline aquifers in 453the Jiyang Depression (Shandong province)[89,90].The results 454show that the Dagang oilfield is not suitable for large-scale storage,455though could be considered for EOR pilots.The Shengli oilfield was 456considered more promising for storage (472Mt in eight selected 457fields).Storage potential in the Kailuan mining area is 504,000458Mt adsorbed onto the coal and 38,100Mt void storage capacity.459However,the coals have low porosity and permeability that will af-460fect future energy resources [90].The Institute of Geology and Geo-461physics,Chinese Academy of Sciences (IGG–CAS)studied the 462potential for storage in the Jiyang Depression.The results revealed 463that Guantao Formation in the Jiyang Depression has good porosity 464and permeability 465areas was 4662010,in South China 467of Sciences 468storage capacity in 469the Pearl River 470CCS-related 471China [78].There 472saline formations 473tive storage 474including 60Mt in 475large for storaging 476in Guangdong in 477In a word,these 478age of CO 2in deep 479Although this is 480countries,it will 481and there was 482characteristics.483 3.1.2.CO 2–EOR484Although CO 2485oil recovery (EOR)486this process can be 487oil,the cost of CO 2,488the CO 2source [92].489the production of 490be an ideal option 49184commercial or 492tion worldwide [1].493been implemented 494Oil Corporation 495in the Daqing,496ernments of Japan 497out a project to 498plant in China into a 499duced from the 500that between 270501ered by using CO 2502including IGG–CAS 503three large oil fields 504oil reservoirs in the 505were suitable both 506found suitable for 507showed that the 508CO 2storage 509the oil recovery by steam injection has been already applied at Lia-510ohe oil field.Each single well,in average,had conducted 7.6times 511of steam injection-oil recovery processing for EOR propose.The to-512tal recovered oil amounts were 12.06Mt [92].Active oil producing 513fields where CO 2–EOR is technically possible provide credible 514opportunities to initiate CO 2storage demonstration projects.How-515ever,significant further investigations,including detailed site516appraisals would be necessary before such fields can be considered 517as technically and economically suitable for CO 2storage.5183.1.3.CO 2–ECBM519In a similar manner,ECBM recovery can be used to store CO 2520while improving methane recovery.A bright prospect of gas injec-521tion technology for ECBM production has been suggested by Chi-522nese engineers since the late 1990s [94].More recently,a joint 523venture was formed between the China United Coal Bed Methane 524Corporation and the Alberta Research Council of Canada to develop 525a project entitled ‘‘Development of China’s coalbed methane tech-526nology/CO 2sequestration’’[12].This project was initiated in March 527project was performed 528in the anthracitic coals of 529China [95],which is 530in China up to now 531at ICC–CAS in 2005532were investigated based 533An equipment simulated 534middle pressures was 535in coal seam,536behaviors were studied.537coal mine and salt-water 538four coals of various rank 539China were tested for 540one of the most impor-541process.The result 542capacities for methane 543>Bulianta coal >Zhangji 544adsorption isotherms 545lattice model [100].546given to estimate the 547[101],which was 548underground stress is so 5492and CH 4respectively 550the mechanical sta-551of the impact factors of 552stress could be obviously 553of the casing or by using 554and Young’s modulus 555China was also estimated 556prospecting data of coal 557and the replacement ratio 558different ranks,it is esti-559methane resources will 560technology is uti-561in coalbeds is about 562as the total CO 2emission 563also developed 564simulation of the CO 2–565is a lack of knowledge 566due to the complexity 567fluid transport processes.568will be the next 569570571Large amounts of CO 2can also be fixed by a process called min-572eral carbonation,which is natural or artificial fixation of CO 2into 573carbonates.It has been proposed as a promising CO 2sequestration 574technology e.g.the silicate rocks (calcium or magnesium)could be 575turned into carbonates by reacting with CO 2following this mech-576anism [8,105]:577ðMg ;Ca Þx Si y O x þ2y þx CO 2!x ðMg ;Ca ÞCO 3þy SiO 25798L.L Q1i et al./Fuel xxx (2011)xxx–xxxPlease cite this article in press as:L Q1i L et al.A review of research progress on CO 2capture,storage,and utilization in Chinese Academy of Sciences.Fuel(2011),doi:10.1016/j.fuel.2011.08.022580581582583584585586587588589590591592593594595596597598599600601602603604605606607608609610611612613614615616617618619620621622623624625626627628629630631632633634635636637638639hanced by the fact that this method of storage is highly verifiable 640and unquestionably permanent,the grinding energy required to 641produce particles of the size required to react rapidly with the 642acids is large,and the residence times on the order of hours re-643quired to allow carbonation of the solids,via either route,is so long 644that immense reactors would be required,associating environmen-645tal concerns.Furthermore,mineral carbonation will always be646expensive than most applications of geological storage 647important gap in mineral carbonation is the lack of 648onstration plant.649Ocean storage650Captured CO 2also could help reduce the atmospheric 6516526536546556566576586596606616626636646656666676686696706716726736746756766776786796806816826836842685carbonic acid,which would be likely harmful to ocean organisms 686and ecosystems [17].Additionally,it is not known whether the 687public will accept the deliberate storage of CO 2in the ocean as part 688of a climate change mitigation strategy.The development of ocean 689storage technology is generally at a conceptual stage;thus,further 690research and development would be needed to make technologies 691available.3.Reaction mechanism for enhanced carbonation crystallization Q1Please cite this article in press as:L Q1i L et al.A review of research progress on CO 2capture,storage,and utilization in Chinese Academy of Sciences.Fuel(2011),doi:10.1016/j.fuel.2011.08.022692693694695696697698699700701702703704705706707708709710711712713714715716717718719721722723the reaction [131–135],such as in ICC–CAS,Zhao et al.had reported 724a catalyst system composed of KI supported on metal oxides for 725cycloaddition of propylene oxide with CO 2.It was found that the 726activity of KI for cycloaddition was greatly enhanced by ZnO as both 727support and promoter,resulting in a high yield of propylene 728carbonate within a short reaction time.The mechanism is also pro-729posed (Scheme 4)[133].Recently,a large number of catalytic730systems,such as metal oxides,transition metal,ammonium 731well as main group complexes,were reported to be active 732reactions [136–139].In ICC–CAS,the efficient ultrasonic tech-733nique was used for the preparation of amine-functionalized porous 734catalysts for CO 2coupling with epoxide.According to 735study by Zhang and co-workers [140],the reaction conditions 736great influence on the performance and the silanols on the surface 737played an important role in the chemical fixation of CO 2.In addi-738they also proposed the possible reaction mechanism for 739coupling with epoxide over such type of catalysts (Scheme 5).740In recent years,ionic liquids as environmentally benign media 741organic synthesis and catalytic reaction significant progress 7427437447457467477487492750catalyst system without using additional organic solvents was 751achieved in excellent selectivity and TOF (5410h À1)[144].In 752IPE–CAS,an efficient Lewis acid/base catalyst composed of ZnCl 2/753PPh 3C 6H 13Br was developed and showed high activity and selectiv-754ity for the coupling reaction of CO 2and epoxide under the mild 755conditions [145].Sun et al.prepared a series of hydroxyl-function-756alized ionic liquids (HFILs)which showed efficient reactivity andScheme 4.The proposed diagram of reaction mechanism [133].Q1Please cite this article in press as:L Q1i L et al.A review of research progress on CO 2capture,storage,and utilization in Chinese Academy of Sciences.Fuel(2011),doi:10.1016/j.fuel.2011.08.022780781782783784785786787788789790791792793794795796797798799800802803804805806807Please cite this article in press as:L Q1i L et al.A review of research progress on CO 2capture,storage,and utilization in Chinese Academy of Sciences.Fuel(2011),doi:10.1016/j.fuel.2011.08.022CO 2þCH 4¼2CO þ2H 2841842In the past decade,a lot of researches have been devoted to the 843catalytic performance of noble metals,including Pt,Ru,Rh,Pd,844and Ir for this reaction [165–169].It showed that Rh and Ru845exhibited both high activity and stability in CH 4dry reforming,846while Pd,Pt and Ir were less active and prone to deactivation.847Nevertheless,considering the aspects of high cost and limitedPlease cite this article in press as:L Q1i L et al.A review of research progress on CO 2capture,storage,and utilization in Chinese Academy of Sciences.Fuel(2011),doi:10.1016/j.fuel.2011.08.022848availability of noble metals,it is more practical to develop non-849noble metal catalysts which exhibited both high activity and pared with noble metals,Ni-based catalysts have been 851widely investigated because of their high activity and relatively 852low price [170–172].Nevertheless,application of Ni-based cata-853lysts in a large scale process is not so straightforward due to rapid 854carbon deposition,resulting in the deactivation of the catalyst 855[173].It was found that when Ni is supported on a alkaline earth 856metal oxide such as MgO,CaO,and BaO with strong Lewis basi-857city,carbon deposition can be attenuated or even suppressed 858[174]which is because that the support could promote chemi-859sorption of CO 2and thus,accelerated the reaction of CO 2and C 8608618628638648658668678688698708718728738748758768778788798808818828838848858868878888898908918928938948958968974.4.Reaction of CO 2with ethane and propane898Ethylene and propylene are basic raw material in the petrol-899chemical industry.Thermal cracking of hydrocarbons (such as eth-900ane)in the presence of steam is currently the main source of eth-901ylene [181,182].Nevertheless,steam cracking of ethane to 902ethylene is a highly endothermic process that must be performed 903at high temperatures,which means the consumption of a large 904amount of energy.The introduction of CO 2could reduce the extent 905of deep oxidation which results in many byproducts whereas eth-906ylene selectivity drops when oxygen is used as oxidant [183].907Thermodynamics analysis and experimental results have indi-908909910911912913915916917918919920921922923924925926927928929930931932933934935936938939940941L.L Q1i et al./Fuel xxx (2011)xxx–xxx13Please cite this article in press as:L Q1i L et al.A review of research progress on CO 2capture,storage,and utilization in Chinese Academy of Sciences.Fuel(2011),doi:10.1016/j.fuel.2011.08.022969970971972973974975976977978979980981982983984985986987988990991992993994995996997998999100010011002100310041005100610071008100910101011101210131014Please cite this article in press as:L Q1i L et al.A review of research progress on CO 2capture,storage,and utilization in Chinese Academy of Sciences.Fuel(2011),doi:10.1016/j.fuel.2011.08.0221015DMC in supercritical phase was proposed in Scheme 11.Recently,developed a supported Cu-Ni/V 2O 5-SiO 2heterogeneous because the reaction can be carried out in a fixed-bed the side production of water molecules 10341035103610371038103910401041104210431044and theoretical approaches,which enable the development of 1045CO 2selective sorbents.Besides,the sorbent performance,lifetime,10461047104810491050105110521053105410551056105710581059106010611062106310641065Scheme 11.The proposed catalytic reaction mechanism Please cite this article in press as:L Q1i L et al.A review of research progress on CO 2capture,storage,and utilization in Chinese Academy of Sciences.Fuel(2011),doi:10.1016/j.fuel.2011.08.0221066of component costs,specific Chinese market conditions,and other 1067factors impacting costs of deployment in China will be important 1068to consider in greater detail.To propose the storage mechanism,1069monitoring,simulation,risk assessment,control methods as well 1070as engineering design will be studied in future.1071The utilization of CO 2to chemicals has attracted considerable 1072attention as a possible way to manufacture useful commercial 1073chemicals from CO 2in some specific locations (Scheme 12)[222].1074The utilization of CO 2as a raw material in the synthesis of chemi-1075cals was also conducted by CAS,including synthesis of cyclic car-1076bonate from CO 2and epoxide,reaction of CO 2and propylene 1077glycol (PG),CO 2reforming of CH 4,reaction of CO 2and ethane 1078and propane,CO 21079methyl carbonate 1080amount of CO 2can 1081to the order of 1082ent the typical 1083cations is only 1084laminates are used 1085of the materials can 1086and overall net 1087ation.1088and fundamental 1089lue-added chemicals 1090tive net carbon 1091moderate reaction 1092the energy or 1093clear,wind,1094also important to 1095 6.Uncited 1096[201].Q31097Acknowledgments1098This work was 1099vation Programme 1100323);the Ministry of 1101lic of China 1102Climate Change:1103Academy of 1104the 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V OL .56,N O .215J ANUARY 1999J O U R N A L O F T H E A T M O S P H E R I C S C I E N C E S ᭧1999American Meteorological Society127SCIAMACHY:Mission Objectives and Measurement ModesH.B OVENSMANN ,J.P .B URROWS ,M.B UCHWITZ ,J.F RERICK ,S.N OE¨L ,ANDV .V .R OZANOVInstitute of Environmental Physics,University of Bremen,Bremen,GermanyK.V .C HANCEHarvard–Smithsonian Center for Astrophysics,Cambridge,MassachusettsA.P .H.G OEDESRON Ruimetonderzoek,Utrecht,the Netherlands(Manuscript received 5September 1997,in final form 16June 1998)ABSTRACTSCIAMACHY (Scanning Imaging Absorption Spectrometer for Atmospheric Chartography)is a spectrometerdesigned to measure sunlight transmitted,reflected,and scattered by the earth’s atmosphere or surface in the ultraviolet,visible,and near-infrared wavelength region (240–2380nm)at moderate spectral resolution (0.2–1.5nm,␭/⌬␭ഠ1000–10000).SCIAMACHY will measure the earthshine radiance in limb and nadir viewing geometries and solar or lunar light transmitted through the atmosphere observed in occultation.The extraterrestrial solar irradiance and lunar radiance will be determined from observations of the sun and the moon above the atmosphere.The absorption,reflection,and scattering behavior of the atmosphere and the earth’s surface is determined from comparison of earthshine radiance and solar irradiance.Inversion of the ratio of earthshine radiance and solar irradiance yields information about the amounts and distribution of important atmospheric constituents and the spectral reflectance (or albedo)of the earth’s surface.SCIAMACHY was conceived to improve our knowledge and understanding of a variety of issues of importance for the chemistry and physics of the earth’s atmosphere (troposphere,stratosphere,and mesosphere)and potential changes resulting from either increasing anthropogenic activity or the variability of natural phenomena.Topics of relevance for SCIAMACHY areR tropospheric pollution arising from industrial activity and biomass burning,R troposphere–stratosphere exchange processes,R stratospheric ozone chemistry focusing on the understanding of the ozone depletion in polar regions as well as in midlatitudes,andR solar variability and special events such as volcanic eruptions,and related regional and global phenomena.Inversion of the SCIAMACHY measurements enables the amounts and distribution of the atmospheric con-stituents O 3,O 2,O 2(1⌬),O 4,BrO,OClO,ClO,SO 2,H 2CO,NO,NO 2,NO 3,CO,CO 2,CH 4,H 2O,N 2O,and aerosol,as well as knowledge about the parameters pressure p,temperature T,radiation field,cloud cover,cloud-top height,and surface spectral reflectance to be determined.A special feature of SCIAMACHY is the combined limb–nadir measurement mode.The inversion of the combination of limb and nadir measurements will enable tropospheric column amounts of O 3,NO 2,BrO,CO,CH 4,H 2O,N 2O,SO 2,and H 2CO to be determined.1.IntroductionLarge and significant changes in the composition and behavior of the global atmosphere have emphasized the need for global measurements of atmospheric constit-uents.Examples are (i)the precipitous loss of Antarctic (WMO 1995)and Arctic stratospheric ozone (O 3)(New-Corresponding author address:Dr.Heinrich Bovensmann,Institute of Environmental Physics,University of Bremen (FB1),P .O.Box 330440,D-28334Bremen,Germany.E-mail:bov@gome5.physik.uni-bremen.deman et al.1997;Mu ¨ller et al.1997)resulting from the tropospheric emission of chlorofluorocarbon com-pounds (CFCs,halones,and HFCs)(WMO 95);(ii)the global increase of tropospheric O 3(WMO 1995);(iii)the observed increase of tropospheric ‘‘greenhouse gas-es’’such as CO 2,CH 4,N 2O,and O 3(IPCC 1996);and (iv)the potential coupling between polar stratospheric ozone loss and increased greenhouse gas concentrations (Shindell et al.1998).To assess the significance of such changes a detailed understanding of the physical and chemical processes controlling the global atmosphere is required.Similarly knowledge about the variability and temporal behavior128V OLUME56J O U R N A L O F T H E A T M O S P H E R I C S C I E N C E Sof atmospheric trace gases is necessary to test the pre-dictive ability of the theories currently used to model the atmosphere.Consequently,the accurate assessment of the impact of current and future anthropogenic ac-tivity or natural phenomena on the behavior of the at-mosphere needs detailed knowledge about the temporal and spatial behavior of several atmospheric trace con-stituents(gases,aerosol,clouds)on a global scale,in-cluding the troposphere.Over the past two decades pioneering efforts have been made by the scientific community to establish both ground-based networks and satellite projects that will eventually result in an adequate global observing sys-tem.Examples of satellite borne elements of such pro-grams are the Solar Backscatter Ultraviolet(SBUV)and Total Ozone Mapping Spectrometer(TOMS)on NASA’s Nimbus-7satellite(Heath et al.1975);the Stratospheric Aerosol and Gas Experiment(SAGE)(McCormick et al.1979);the Upper Atmosphere Research Satellite (UARS)(Reber et al.1993)with the Microwave Limb Sounder(MLS),the Halogen Occultation Experiment (HALOE),the Cryogenic Limb Array Etalon Spectrom-eter(CLAES),and the Improved Stratospheric and Me-sospheric Sounder(ISAMS)instruments on board;and the Second European Remote Sensing satellite(ERS-2), which carries the Global Ozone Monitoring Experiment (GOME)(Burrows et al.1999).In the near future,sev-eral new missions will be launched and will contribute significantly to research in thefields of atmospheric chemistry and physics:NASA’s Earth Observing System (EOS)satellites EOS-AM and EOS-CHEM,the Japa-nese Advanced Earth Observing System(ADEOS),and the European Space Agency’s(ESA)Environmental Satellite(ENVISAT).The Scanning Imaging Absorption Spectrometer for Atmospheric Chartography(SCIAMACHY)is part of the atmospheric chemistry payload onboard ENVISAT being prepared by ESA.Following the call for earth observation instrumentation in the Announcement of Opportunity for the Polar Platform issued by ESA,the SCIAMACHY proposal(Burrows et al.1988)was sub-mitted to ESA by an international team of scientists led by Principal Investigator J.P.Burrows.After peer re-view SCIAMACHY was selected as part of the payload for the satellite now known as ENVISAT,which is planned to be launched in2000.The heritage of SCIAMACHY(Burrows et al.1988) lies in both the ground-based measurements using Dif-ferential Optical Absorption Spectroscopy(DOAS) (Brewer et al.1973;Platt and Perner1980;Solomon et al.1987)and previous satellite atmospheric remote sensing missions.SCIAMACHY combines and extends the measurement principles and observational modes of the nadir scattered sunlight measuring instruments SBUV and TOMS(Heath et al.1975),the solar occul-tation instrument SAGE(McCormick et al.1979;Maul-din et al.1985),and the limb scattered sunlight mea-suring instrument Solar Mesospheric Explorer(SME)(Barth et al.1983)within one instrument.SCIAMA-CHY measures in the wavelength range from240nm to2380nm the following:R The scattered and reflected spectral radiance in nadir and limb geometry,R the spectral radiance transmitted through the atmo-sphere in solar and lunar occultation geometry,and R the extraterrestrial solar irradiance and the lunar ra-diance.Limb,nadir,and occultation measurements are planned to be made during every orbit.Trace gases,aerosols, clouds,and the surface of the earth modify the light observed by SCIAMACHY via absorption,emission, and scattering processes.Inversion of the radiance and irradiance measurements enables the amounts and dis-tributions of a significant number of constituents to be retrieved from their spectral signatures and is discussed in section4.Figure1shows the wavelength range to be observed by SCIAMACHY and the position of spec-tral windows where atmospheric constituents are to be retrieved.SCIAMACHY and GOME,which is a small-scale version of SCIAMACHY(see Burrows et al.1999and references therein),represent a new generation of space-based remote sounding sensors,which rely on and uti-lize the simultaneous spectrally resolved measurement of light upwelling from the atmosphere to determine amounts of atmospheric constituents.Using data from GOME,which was launched on board the European Remote Sensing satellite ERS-2in April1995,the feasibility of the instrument and retrieval concepts have been successfully demonstrated for nadir observations.The trace gases O3,NO2,BrO,OClO, SO2,and H2CO have been observed as predicted(Bur-rows et al.1999),and studies of ClO,NO,and aerosol retrieval are proceeding.The determination of O3profile information,including tropospheric O3,from GOME measurements(Burrows et al.1999;Munro et al.1998; Rozanov et al.1998)has a large number of potential applications.In addition,the retrieval of tropospheric column information of SO2,H2CO,NO2,and BrO from GOME measurements was demonstrated(Burrows et al. 1999).The goal of this paper is to provide a comprehensive overview of the SCIAMACHY mission and instrument, to summarize the retrieval strategies,to report on planned data products and expected data quality,and to demonstrate the range of applications and the potential that lies in the concept of this new generation of hy-perspectral UV–VIS–NIR sensors.Section2provides details about the targeted constituents.In section3the instrument design and observational modes are pre-sented.The proposed retrieval strategies are summa-rized in section4.Section5focuses on the expected data precision and section6summarizes the current sta-tus of operational data products.15J ANUARY 1999129B O V E N S M A N N E T A L.F IG .1.Wavelength range covered by SCIAMACHY and absorption windows of the targeted constituents.2.Scientific objectives and targeted constituents The main objective of the SCIAMACHY mission is to improve our knowledge of global atmospheric change and related issues of importance to the chemistry and physics of our atmosphere (cf.WMO 1995and IPCC 1996)such asR the impact of tropospheric pollution arising from in-dustrial activity and biomass burning,R exchange processes between the stratosphere and tro-posphere,R stratospheric chemistry in the polar regions (e.g.,un-der ‘‘ozone hole’’conditions)and at midlatitudes,and R modulations of atmospheric composition resulting from natural phenomena such as volcanic eruptions,solar output variations (e.g.,solar cycle),or solar pro-ton events.Figure 2lists the constituents targeted by SCIA-MACHY and shows the altitude where measurements are to be made.In Fig.2,the combined use of nadir and limb measurements is assumed to yield tropospheric amounts of the constituents down to the ground or the cloud top,depending on cloud cover.a.Tropospheric chemistrySCIAMACHY will measure the backscattered sun-light that reaches the earth’s surface (␭Ն280nm).The retrieval of tropospheric constituents is influenced and limited by clouds.SCIAMACHY is the only atmo-spheric chemistry sensor on ENVISAT capable of de-termining trace gases and aerosol abundances in the lower troposphere including the planetary boundary lay-er under cloud-free conditions.From the SCIAMACHY nadir and limb measurements tropospheric columns of O 3,NO 2,BrO,CO,CH 4,H 2O,N 2O,SO 2,and H 2CO (cf.Fig.2)will be retrieved.In addition,surface spectral reflectance,aerosol and cloud parameters (cover and cloud-top height),and the tropospheric flux from 280to 2380nm will be retrieved.These data are required for studies of the oxidizing capacity of the troposphere,photochemical O 3production and destruction,and tro-pospheric pollution (biomass burning,industrial activ-ities,aircraft).b.Stratosphere–troposphere exchangeFor the investigation of stratosphere–troposphere ex-change (Holton et al.1995)SCIAMACHY measure-130V OLUME 56J O U R N A L O F T H E A T M O S P H E R I C S C I E N C ES F IG .2.Altitude ranges of atmospheric constituents targeted by SCIAMACHY.Retrieval from the occultation measurements yields infor-mation over a wider altitude range than the limb measurements,due to its higher S/N ratio.ments of the height-resolved profiles of the tracers O 3,H 2O,N 2O,CH 4,and aerosol will be of primary sig-nificance.These measurements enable investigations of the downward transport of stratospheric O 3and upward transport of important species (e.g.,aerosol,CH 4,H 2O,and N 2O).The CH 4and N 2O molecules are emitted into the planetary boundary layer.Their long tropospheric lifetime results in being transported to the stratosphere,where they are the dominant source of the ozone-de-stroying HO x and NO x radicals.Studies of relatively small-scale features such as tropopause folding at mid-latitudes require a high spatial resolution and are un-likely to be unambiguously observed by SCIAMACHY .However,larger-scale stratosphere–troposphere ex-change as envisaged by Holton et al.(1995)will be readily observed.In the neighborhood of the tropopause the different measurements modes of SCIAMACHY will have dif-ferent vertical and horizontal resolutions.Solar and lu-nar occultation modes yield measurements with a ver-tical resolution of 2.5km and a horizontal resolution of 30km across track,determined by the solar diameter,and extending roughly 400km along track.For the limb measurements the geometrical spatial resolution is ap-proximately 3km vertically and typically 240km hor-izontally across track,determined by scan speed and integration time,and extending roughly 400km along track (see Table 3).More details about the geometricalresolution of the different measurement modes will be given in section 3b.c.Stratospheric chemistry and dynamicsThe study of the stratospheric chemistry and dynam-ics will utilize the simultaneous retrieval of total col-umns from nadir measurements and vertical stratospher-ic profiles from limb and occultation measurements of O 3,NO 2,BrO,H 2O,CO,CH 4,and N 2O (and OClO and possibly ClO under ozone hole conditions),as well as aerosol and stratospheric cloud information.Tem-perature and pressure profiles can be determined from limb and occultation observations of the well-mixed gases CO 2and O 2assuming local thermal equilibrium.SCIAMACHY will be making measurements when halogen loading of the stratosphere maximizes around the turn of the century (WMO 1995).It has recently been pointed out by Hofmann (1996)that the springtime polar lower-stratospheric O 3,specifically the layer from 12to 20km,will be the first region to show a response to the international control measures on chlorofluoro-carbon compounds (CFCs)defined in the Montreal Pro-tocol of 1987and its Copenhagen and London amend-ments.SCIAMACHY will enable this preposition to be studied in detail.In general,SCIAMACHY measurements will yield detailed information about the development of strato-15J ANUARY 1999131B O V E N S M A N N E T A L .spheric O 3above the Arctic and Antarctica,the global stratospheric active halogen species (BrO,ClO,OClO),and the global O 3budget as a function of the height in the atmosphere.As SCIAMACHY measures simulta-neously the backscattered radiation field and constituent profiles,an important objective is to test the accuracy of current stratospheric photochemical models and their predictive capability.d.Mesospheric chemistry and dynamicsIn the upper stratosphere and lower mesosphere SCIAMACHY measurements yield profiles of O 3,H 2O,N 2O,NO,O 2,and O 2(1⌬).These measurements will be used to study the distribution of H 2O and O 3and their global circulation.There has recently been much dis-cussion of upper-stratospheric and mesospheric chem-istry in the context of the ‘‘ozone deficit problem’’(Crutzen at al.1995;Summers et al.1997).It has also been suggested that monitoring of H 2O in the lower mesosphere may offer an opportunity for the early de-tection of climate change (Chandra et al.1997).The O 3destruction by mesospheric and upper-stratospheric NO will be investigated.Finally,the mesospheric source of stratospheric NO x will be quantified.In contrast to the retrieval of the majority of trace gases from SCIAMACHY data,NO and O 2(1⌬)profiles are to be determined from their emission features rather than their absorptions.Satellite measurements of NO via the ␥-band emission had been demonstrated by SME to determine profile information from the limb scan (Barth et al.1983,1988)and by SBUV to determine column amounts above 45km from nadir measurements (McPeters 1989).NO can be detected above 40km via the emission from the excited A 2⌺ϩstate into the ground state X 2⌸1/2,3/2(NO ␥-band transitions,200–300nm)as determined in a model sensitivity study by Frederick and Abrams (1982).SCIAMACHY will be able to detect several bands in the 240–300-nm spectral region of the ␥-band emissions of NO in limb as well as in nadir observation mode.O 2(1⌬)can be detected using its emission around 1.27␮m as shown by results from the SME (Thomas et al.1984).The combination of height-resolved O 3,O 2(1⌬),and UV radiance products from SCIAMACHY provides detailed information about the photolysis of O 3in the upper stratosphere and mesosphere.This will provide an excellent opportunity to test our current photochem-ical knowledge of the mesosphere.e.Climate researchFor use in climate research,SCIAMACHY measure-ments will provide the distributions of several important greenhouse gases (O 3,H 2O,CH 4,N 2O,and CO 2),aero-sol and cloud data,surface spectral reflectance (280–2380nm),the incoming solar spectral irradiance and the outgoing spectral radiance (240–2380nm),and pro-files of p and T (via O 2and CO 2).As it is intended that SCIAMACHY observations are to be made for many years,this long-term dataset will provide much unique information useful for the study of the earth–atmosphere system and variations of the solar output and its impact on climate change.To reach continuity with other spec-trometers measuring solar spectral irradiance such as SBUV or GOME,it is foreseen that SCIAMACHY will be calibrated with standard methods also applied to the GOME or SBUV calibration (Weber et al.1998).3.The instrumentDetails of the instrument concept and design have been given by Burrows and Chance (1991),Goede et al.(1994),Burrows et al.(1995),and Mager et al.(1997).The design is summarized in the following sub-sections.Since the development of the design of SCIA-MACHY two significant changes have occurred.1)The original concept (Burrows and Chance 1991;Burrows et al.1995)used an active Stirling cooler to maintain the infrared detectors of SCIAMACHY at their operational temperature of 150K.During the development phase it was found that a passive cooler could be used for this purpose.This has the advantage of reducing the electrical power con-sumption and potentially extending the lifetime of the mission.2)As an outcome of phase B studies an additional sev-enth polarization measurement device (PMD),mea-suring the 45Њcomponent of the incoming radiance,was added to the spectrometer,to improve the ra-diometric accuracy for the limb mode.a.Design and performanceThe SCIAMACHY instrument is a passive remote sensing moderate-resolution imaging spectrometer.It comprises a mirror system,a telescope,a spectrometer,and thermal and electronic subsystems.A schematic view of the light path within the instrument is depicted in Fig.3.The incoming radiation enters the instrument via one of three ports.1)For nadir measurements the radiation from the earth’s scene is directed by the nadir mirror into a telescope (off-axis parabolic mirror),which focuses the beam onto the entrance slit of the spectrometer.2)For limb and solar/lunar occultation measurements the radiation is reflected by the limb (elevation)mir-ror to the nadir (azimuth)mirror and then into the telescope,which focuses the beam onto the entrance slit of the spectrometer.3)For internal and subsolar calibration measurements the radiation of internal calibration light sources or the solar radiation is directed by the nadir mirror into the telescope.Except for the scan mirrors,all spectrometer parts are132V OLUME 56J O U R N A L O F T H E A T M O S P H E R I C S C I E N C ES F IG .3.Schematic view of the SCIAMACHY optical layout.All imaging optical components (mirrors,redirecting prisms,lenses,etc.)areomitted.All used gratings are in a fixed position.Each detector contains a 1024-pixel photo diode array.fixed and the spectra are recorded simultaneously from 240to 1750nm and in two smaller windows,1940–2040nm and 2265–2380nm,in the near-infrared.The solar radiance varies by a factor of about 100between 240and 400nm.In comparison,the earthshine radiance varies approximately four orders of magnitude over the same spectral range.Spectrometers that measure these quantities therefore need to suppress well any stray light within the instrument.The SCIAMACHY spectrometer achieves this by the combination of a predispersing prism and gratings.This is equivalent in principle to a double spectrometer design.Initially light from the spectrometer slit is collimated and directed onto the pre-dispersing prism.The main beam of light leaving the predispersing prism forms a spectrum in the middle of the instrument.Reflective optics are used to separate the spectrum into four parts.The shorter wavelengths of the spectrum are directed to channel 1(240–314nm)and channel 2(314–405nm)respectively.The majority of the light in the spectrum (405–1750nm)passes without reflection to channels 3–6.The infrared part of the spec-trum (1940–2380nm)is reflected toward channels 7and 8.Dichroic mirrors are used to select the wavelength ranges for channels 3,4,5,and 6,and to separate light for channel 7from that for channel 8.Each individual channel comprises a grating,transmission optics,and a diode array detector.The grating further disperses the light,which is then focused onto eight linear 1024pixel detector arrays.To minimize detector noise and dark current,the diode arrays are cooled:the detector for channels 1and 2to 200K,those for channels 3–5to 235,that for channel 6to 200K,and those for channels 7and 8to 150K.The entire instrument is cooled to 253K in order to minimize the infrared emission from the instrument that might influence the detectors of channels 6–8.In channels 1–5the detectors are silicon monolithic diode arrays (EG&G Reticon RL 1024SR).For the NIR channels 6to 8InGaAs detectors were developed by Epitaxx,Inc.(Joshi et al.1992),and space qualified specifically for SCIAMACHY (see, e.g.,Goede et al.1993;van der A et al.1997).The spectral and radiometric characteristics of the SCIAMACHY spectrometer are summarized in Table 1.The spectral resolution of the spectrometer varies be-tween 0.24and 1.48nm depending on channel number (see Table 1).For DOAS retrieval (see section 4)a high spectral stability is required.The instrument is designed to have a spectral stability of 1/50of a detector pixel,which requires a temperature stability of the spectrom-eter of better than 250mK over one orbit in combination with dedicated calibration measurements.The second relevant retrieval strategy (see section 4),the Full Re-trieval Method (FURM)based on optimal estimation (Rodgers 1976),requires in addition to high spectral stability a high radiometric accuracy of the SCIAMA-CHY measurements.Knowledge of the state of polar-ization of the incoming light and the polarization re-sponse of the instrument determines the radiometric ac-curacy of the radiance,irradiance,and higher-level data products.To achieve the required radiometric accuracy15J ANUARY1999133B O V E N S M A N N E T A L.T ABLE1.Optical parameters of the spectrometer from the designanalysis.ChannelSpectralrange(nm)Resol-ution(nm)Stability(nm)High-resolution channels 1234240–314309–405394–620604–8050.240.260.440.480.0030.0030.0040.005 5678785–10501000–17501940–20402265–23800.541.480.220.260.0050.0150.0030.003Polarization measurement devices PMD1PMD2PMD3PMD4310–377450–525617–705805–900broadbandbroadbandbroadbandbroadband PMD5PMD6PMD71508–16452265–2380802–905broadbandbroadbandbroadbandRadiometric accuracy2–4%Ͻ1%absoluterelativeof2%–4%(depending on the spectral region),dedicated on-ground and in-flight radiometric calibration mea-surements have to be performed in combination with measurements of the polarization properties of the at-mosphere.For the latter purpose SCIAMACHY is equipped with seven polarization measurement devices. Six of these devices(PMD1–6)measure light polarized perpendicular to the SCIAMACHY optical plane,gen-erated by a Brewster angle reflection at the second face of the predispersing prism.This polarized beam is split into six different spectral bands,as described in Table 1.The spectral bands are quite broad and overlap with spectral regions of channels2,3,4,5,6,and8.The PMDs and the light path to the array detectors(including the detectors)have different polarization responses. Consequently,the appropriate combination of PMD data,array detector data,and on-ground polarization calibration data enables the polarization of the incoming light for the nadir measurements(Kruizinga et al.1994; Frerick et al.1997)to be determined.For atmospheric limb measurements,where both limb and nadir mirrors are used,the light is off the optical plane of the spec-trometer.This requires the measurement of additional polarization information of the incoming light.A sev-enth PMD(PMD7)will therefore measure the45Њcom-ponent of the light extracted from the channels3–6light path,as depicted in Fig.3.All PMDs are read out every 1/40s and they observe the same atmospheric volume as channels1–8.In addition to these PMD data being used for the determination of the polarization charac-teristics of the incoming light,they are also planned to be used to determine the fractional cloud cover of the observed ground scene.Additional information about the polarization of the incoming light can be obtained from the diode array overlap regions1/2(309–314nm),2/3(394–405nm), 3/4(604–620nm),4/5(785–805nm),and5/6(1000–1050nm).The polarization efficiency is different for the measurements of the same wavelength in the dif-ferent channels.Inversion of these measurements yields the ratio of plane to parallel polarization components of the incoming light in a manner similar to that used for the array and PMD detectors.The advantage of the over-lap regions is that they are in small wavelength bands, having the same spectral resolution as the corresponding channel.SCIAMACHY aims to retrieve trace gas amounts of relatively weak absorbers.For example,the dif-ferential optical density due to the BrO absorption around350nm detected with GOME(Burrows et al. 1999)is in the order of10Ϫ3and below.Therefore, to achieve a high retrieval precision,a high signal-to-noise ratio(S/N)is required for the scattered ra-diance as well as for the solar irradiance and lunar radiance from the UV to the NIR.The predicted in-strumental S/N values as a function of wavelength are depicted in Fig.4.These S/N values are calculated for an individual detector pixel,for example,of nadir, limb,and occultation measurements.In most cases the predicted S/N is well above103.Exceptions are found in channels1,7,and8.In channel1S/N de-creases toward the UV primarily because the sun is weaker and ozone absorption increases strongly from 320to250nm.In the IR channels7and8the lower S/N values arise from the higher noise of the InGaAs detectors.For these channels the S/N is limited by the detector noise.The apparent missing S/N in Fig. 4c for channel1is the result of the almost complete absorption of the solar photons by the ozone layer when observing the tangent height of15km.In gen-eral,higher S/N values can be obtained by averaging measurements either temporally or spectrally at the cost of losing temporal(and consequently spatial)or spectral resolution.This strategy enables the optimal set of radiance and irradiance data to be generated for a given inversion.Summation of succeeding mea-surements on board(so-called onboard co-adding)is to be used to match optimally the amount of down-linked data to the ENVISAT data rate allowed for SCIAMACHY.In order to cope with the large dy-namic range of the input signals(limb scattered ra-diance vs solar irradiance),which is of six to eight orders of magnitude,the exposure time of each chan-nel can be selected independently over a wide range of values from0.03125to80s.In addition,an ar-rangement involving an aperture stop and a neutral densityfilter is used to limit the intensity of the in-coming light during solar occultation measurements. To optimize S/N over the orbit,exposure times are varied as a function of the solar zenith angle.To calibrate the instrument inflight and to monitor the instrument performance,SCIAMACHY is equipped with a Pt/Cr/Ne hollow cathode(spectral calibration),a。

Atmospheric Chemistry and PhysicsAtmospheric chemistry and physics are two branches of science that are closely related to each other. The atmosphere, which consists of different gases, plays a vital role in regulating the Earth's climate. The study of atmospheric chemistry and physics helps us understand the chemical and physical processes that occur in the atmosphere. This, in turn, helps us understand how human activities affect the Earth's climate.Atmospheric ChemistryAtmospheric chemistry deals with the chemical reactions that take place in the atmosphere. These chemical reactions involve different gases, such as carbon dioxide, methane, and ozone. Many of these gases are greenhouse gases, which means they contribute to the warming of the Earth's atmosphere.One of the most important chemical reactions that occur in the atmosphere is the formation of ozone. Ozone is a molecule made up of three oxygen atoms. It is present in two layers of the Earth's atmosphere: the stratosphere and the troposphere. In the stratosphere, ozone plays a vital role in protecting the Earth's surface from harmful ultraviolet radiation. In the troposphere, however, ozone is a pollutant that can harm human health and the environment.Other important chemical reactions that occur in the atmosphere include the production of acid rain and the formation of smog. Acid rain is formed when sulfur dioxide and nitrogen oxides react with water vapor in the atmosphere. This can damage ecosystems and harm human health. Smog is formed when pollutants, such as nitrogen oxides and volatile organic compounds, react with sunlight. This can cause respiratory problems for humans and damage plant life.Atmospheric PhysicsAtmospheric physics deals with the physical properties of the atmosphere. This includes the study of atmospheric dynamics, which is the study of how air moves in theatmosphere. Atmospheric dynamics is important because it affects weather patterns and climate.Another important area of atmospheric physics is the study of radiation and energy transfer in the atmosphere. The Earth's atmosphere absorbs and reflects both incoming and outgoing radiation. This plays a crucial role in regulating the Earth's temperature. Atmospheric physics helps us understand how this radiation and energy transfer occurs.The study of atmospheric physics also includes the study of clouds. Clouds are an important part of the Earth's climate system because they reflect sunlight and trap heat. The study of clouds helps us understand how they form, how they affect the Earth's climate, and how they are affected by climate change.ConclusionIn conclusion, atmospheric chemistry and physics are two branches of science that are crucial for understanding the Earth's climate. The study of atmospheric chemistry helps us understand the chemical reactions that occur in the atmosphere, which in turn helps us understand how human activities affect the Earth's climate. The study of atmospheric physics helps us understand the physical properties of the atmosphere, including atmospheric dynamics, radiation and energy transfer, and the formation and behavior of clouds. Together, atmospheric chemistry and physics provide a comprehensive understanding of the Earth's climate system and the role that humans play in affecting it.。

ClickHereforFullArticleLong GPS coordinate time series:Multipath and geometry effectsMatt A.King1and Christopher S.Watson2Received16April2009;revised1October2009;accepted21October2009;published3April2010.[1]Within analyses of Global Positioning System(GPS)observations,unmodeledsubdaily signals propagate into long‐period signals via a number of different mechanisms.In this paper,we investigate the effects of time‐variable satellite geometry andthe propagation of a time‐constant unmodeled multipath signal.Multipath reflectors atH=0.1m,0.2m,and1.5m below the antenna are modeled,and their effects on GPScoordinate time series are examined.Simulated time series at20global IGS sites for2000.0–2008.0were derived using the satellite geometry as defined by daily broadcastorbits.We observe the introduction of time‐variable biases in the time series of up toseveral millimeters.The frequency and magnitude of the signal is dependent on sitelocation and multipath source.When adopting realistic GPS observation geometriesobtained from real data(e.g.,including the influence of local obstructions and hardwarespecific tracking),we observe generally larger levels of coordinate variation.In thesecases,we observe spurious signals across the frequency domain,including very highfrequency abrupt changes(offsets)in addition to secular trends.Velocity biases of morethan0.5mm/yr are evident at some sites.The propagated signal has noise characteristicsthat fall between flicker and random walk and shows spectral peaks at harmonics ofthe draconitic year for a GPS satellite(∼351days).When a perfectly repeating synthetic constellation is used,the simulations show near‐negligible time correlated noisehighlighting that subtle variations in the GPS constellation can propagate multipathsignals differently over time,producing significant temporal variations in time series.Citation:King,M.A.,and C.S.Watson(2010),Long GPS coordinate time series:Multipath and geometry effects,J.Geophys. Res.,115,B04403,doi:10.1029/2009JB006543.1.Introduction[2]Geophysical interpretation of GPS coordinate time series most commonly involves the determination of rates of crustal motion and amplitudes and phases of periodic motions caused by seasonal mass loads(for example, atmospheric,hydrological,or oceanic)[Dong et al.,2002; van Dam and Wahr,1998].Each geophysical parameter of interest derived from long GPS time series is biased at some level by residual systematic error,particular those that manifest as long‐period spurious trends or(quasi)periodic signals.In the case of GPS,these systematic errors and their propagation into GPS time series are not yet all well understood.Recent literature has highlighted that long‐period systematic errors may occur in coordinate time series due to one of two primary mechanisms.[3]First,spurious signals may occur directly due to unmodeled long‐period signals,such as satellite antenna modeling errors that propagate differently as the satellite constellation changes[Ge et al.,2005].The second origi-nates in the presumption that all subdaily signals are mod-eled at the observation level,either completely within the functional model or through partial mitigation from the sto-chastic model(e.g.,elevation‐dependent weighting).How-ever,this is not yet the case and residual subdaily(systematic) errors remain which have been shown to propagate into time series[e.g.,Penna et al.,2007]due to a combination of dif-ferent mechanisms[e.g.,Stewart et al.,2005].[4]One well‐studied example of how subdaily signals propagate into longer‐period signals is the case of an un-modeled subdaily tidal signal.Unmodeled semidiurnal and diurnal signals at certain tidal periods have been shown to propagate into fortnightly,semiannual and annual periods [Penna and Stewart,2003;Stewart et al.,2005]with admit-tances exceeding100%in some cases[Penna et al.,2007]. The propagated signal was shown to be highly sensitive to input signal frequency,coordinate component of the un-modeled signal and site location.King et al.[2008]showed that,even after modeling for solid earth tides and ocean tide loading displacements,substantial signal at subdaily periods remained in GPS coordinate time series and these propagate into annual and semiannual periods in24h solutions with median amplitudes of∼0.5mm,but reaching several milli-meters at several sites.As indicated,studies of seasonal geophysical loading phenomena[e.g.,Blewitt et al.,2001;1School of Civil Engineering and Geosciences,Newcastle University,Newcastle upon Tyne,UK.2Surveying and Spatial Science Group,School of Geography andEnvironmental Studies,University of Tasmania,Hobart,Tasmania,Australia.Copyright2010by the American Geophysical Union.0148‐0227/10/2009JB006543JOURNAL OF GEOPHYSICAL RESEARCH,VOL.115,B04403,doi:10.1029/2009JB006543,2010B044031of23Wu et al.,2003]are therefore adversely affected,as are esti-mates of linear velocity,by the presence of such systematic errors.[5]Systematic errors in least squares solutions,such as used in GPS data analysis,propagate according to the least squares design matrix.Therefore,the propagation mecha-nism is controlled by the observation geometry(as defined by the receiver location(s),satellite constellation and local obstructions)plus the chosen parameterization of the solu-tion.Parameters typically include(but are not limited to) site coordinates,adjustments to tropospheric zenith delay, atmospheric gradients,phase ambiguity terms(when not fixed to integers)and receiver clocks(depending on the data differencing approach adopted).Temporal variations in the observation geometry or the number or type of parameters estimated will therefore likely produce temporal variations in the propagated signal.[6]It is notable,therefore,that even in the trivial yet unrealistic case of the GPS antenna location and number of estimated parameters remaining constant with time,the GPS satellite constellation is constantly evolving as satellites are commissioned and decommissioned,or removed from the solution due to satellite eclipse or maneuver.Furthermore, site specific obstructions such as vegetation or man‐made structures may change with time,producing a further change in the observation geometry.The consequence is that,even if an unmodeled signal remains completely constant in time, the way in which it will propagate is likely to change with time.If these temporal variations are suitably large,then the ensuing systematic error will likely bias the GPS time series significantly,resulting in erroneous interpretation of geo-physical signals such as tectonic velocity,glacial isostatic adjustment,vertical motion of tide gauges or seasonal geophysical loading signals.Furthermore,such errors would degrade the GPS contribution to the International Terrestrial Reference Frame[Altamimi et al.,2007].[7]In this paper we test this hypothesis,using one source of presently unmodeled subdaily signal:carrier phase mul-tipath,taking“multipath”to mean signal reflections from planar surfaces not part of the antenna itself,as adopted by Georgiadou and Kleusberg[1988].Errors of this type are similar in nature to antenna phase center variation mis-modeling and antenna imaging(changes in the antenna phase pattern induced by conducting material in the vicinity of the antenna)[Georgiadou and Kleusberg,1988],in that they exhibit an elevation dependency.We do not consider these additional sources of systematic error here,yet simply note that the propagation mechanism is likely to be some-what similar.Early studies investigating multipath found very small effects on geodetic time series,leading to the thought that multipath effects are mitigated by averaging when sufficient observational time spans are used[e.g., Davis et al.,1989;Lau and Cross,2007a].However,years of experience with continuous GPS time series,combined with analysis advances leading to improved signal‐to‐noise ratio of long time series,have shown that GPS time series are highly sensitive to GPS hardware changes(including receiver,receiver firmware and antenna),suggesting that multipath may be playing an important role;yet the mech-anism for this is not well understood.As a contribution to understanding the effect of carrier phase multipath on multiyear GPS coordinate time series,we perform several trials using simulated and real data,using various simulated carrier phase multipath signals.[8]We commence in section2by introducing the adopted model of carrier phase multipath that we use throughout this paper to perturb a multiyear,simulated GPS coordinate time series.The simulation approach is introduced(section2.2) before detailing the different satellite constellation config-urations adopted to assess the different characteristics of the multipath propagation(section2.3).First,in order to show the influence of time variability on the propagation,we start with a theoretical constellation that has a fixed orbit repeat time,a constant number of satellites and no obstructions above the elevation mask at each site(section 2.3.1). Second,we adopt the same clear horizon but with a realistic time variable satellite constellation taken from the broadcast orbits,(section2.3.2).Finally,we detail the most realistic constellation that includes site specific time variable changes to the observation tracking as observed in real data (for example hardware changes and physical obstructions on the horizon,section2.3.3).[9]In section3we compare and discuss the simulated time series generated using the three constellation config-urations,in addition to investigating the effect of changes to the adopted functional and stochastic models within the evolving constellation scenario.In section4,we pro-vide a comparison against time series computed using real data in a PPP approach with GIPSY5software[Webb and Zumberge,1995],and in section5we present two possible mitigation strategies that involve novel weighting strategies of the input observations in order to minimize the time‐and geometry‐dependent propagation of the multipath signal.2.Simulations2.1.Signal Multipath[10]The space surrounding an antenna may be subdivided into three regions including the reactive near field in the region nearest the antenna,the radiating near field and the far field out to infinity[e.g.,Balanis,2005].The boundaries of these regions are not sharply defined although criteria have been developed in order to delineate them in practice. Given an antenna with maximum dimension D,and signal with wavelength l,and for D>l[Balanis,2005]defines the first and second boundaries occurring at distancesR1¼0:62ffiffiffiffiffiffiD2rand R2¼2D2from the antenna surface,respectively.For a GPS choke ring antenna with D=0.38m,l L1=0.19m and l L2=0.24m, then R1L1=0.03m,R1L2=0.02m,R2L1=1.52m and R2L2=1.20m.In this paper we consider multipath sources solely within the radiating near field,or distances in the range ∼0.03m to∼1.2–1.5m.For an examination of the effect of reactive near field sources on GPS time series,see Dilssner et al.[2008],and for the effect of phase center modeling errors on site velocities,see Steigenberger et al.[2009]. [11]To date there is no widely accepted model for multi-path,partly due to the complexity of real world GPS antenna environments.One relatively simple model shown to approx-imate observed multipath has been described by EloseguiKING AND WATSON:MULTIPATH AND GEOMETRY EFFECTS ON GPS B04403 B044032of23et al.[1995],based on the earlier work of Georgiadou and Kleusberg [1988]and Young et al.[1985].This model is based on the assumption that multipath is caused solely by a horizontal reflector at some height,H ,below the GPS antenna phase center causing an attenuation,a ,of the signal voltage amplitude.So,for a satellite with elevation angle,",phase bias d L (in units of meters)of the L1or L2phase due to multipath may be modeled as [Elosegui et al.,1995]L ¼ 2 tan À1 sin 4 Hsin "!1þ cos 4 Hsin "!0B B @1C C A ð1Þwhere l is the carrier phase wavelength for the L1or L2carrier phase signal.Since most geodetic GPS positioning is performed using the ionosphere ‐free linear combination (LC)of the raw carrier phase observables (L1and L2),the LC phase delay can be computed asLC L "; ;H ðÞ%2:5457Â L "; ;H ; L 1ðÞÀ1:5457Â L "; ;H ; L 2ðÞð2Þ[12]We show in Figure 1(left)d LLC for a range of heights above the reflector (H =0.1,0.2,and 1.5m)and for two different attenuation values (a =0.05and 0.1).As noted by Elosegui et al.[1995],the effect of changing the height above the reflector is to change the rate at which d L LC varies with elevation (increased rate of variation with increasing height).Within a reasonable range of attenuation values (0.01to 0.1),a change in attenuation has the effect ofapproximately uniformly scaling the bias as seen by com-paring Figure 1(left).[13]Despite this model providing a useful approximation,it is based on geometric ray optics which is not appropriate in the radiating near field.In addition,values of d L LC will be modified by the antenna gain pattern.To improve on this,we adopt a model as developed by T.A.Herring (personal communication,2009,hereafter denoted HMM)that extends the Elosegui et al.[1995]model through the use of Fresnel equations relating to electric field amplitudes,and attempting to take into account antenna gain properties:L ¼2 tan À1a sin 4 H sin "ÂÃg d þa cos 4 Hsin "ÂÃ!ð3Þwith the antenna gain pattern,consisting of the direct (g d )andreflected (g r )gain,modeled using a simple modified dipole model expressed as a function of rate of change (G )of the antenna gain with signal zenith angle,such thatg d ¼cos z =G ðÞg r ¼cos 90=G ðÞ1Àsin "ðÞðÞalso,a =Sg r R a is the amplitude of the reflected signal for agiven surface roughness (S ),withR a ¼n 1cos z Àffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffin 22Àn 1sin z ðÞ2q n 1cos z þffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffin 22Àn 1sin z ðÞ2q 264375being the Fresnel equation for an electric field perpendicularto the plane ofincidence.Figure 1.Carrier phase bias due to reflectors using two different multipath models.(left)The Elosegui et al.[1995]model with two different attenuation values,a ,at H =0.1m (gray),H =0.2m (blue),and H =1.5m (magenta),sampled every 1°.(right)The HMM for the same values of H and with two different surface reflectivity terms,S ,sampled every 1°.Np is the refractive index of the reflective medium.The dotted black line (bottom right)is for S =1.0for H =0.16m.KING AND WATSON:MULTIPATH AND GEOMETRY EFFECTS ON GPS B04403B044033of 23[14]This depends on refractive indices n 1and n 2,with n 1=1for air and n 2appropriate for the reflective medium.In practice this can be derived from the square root of tabulated dielectric constants,and for concrete this is typi-cally taken as 4(n 2=2).[15]Here d LLC may be formed analogously to equation (2).[16]For the purposes of this paper we adopt values which approximate the amplitude of the signal in GPS phase residuals (T.A.Herring,personal communication,2009),namely S =0.3,G =1.1and n 2=2,although these are not definitive,and indeed some sites may require a different value of S ,as we shall demonstrate.We show in Figure 1(right)d L LC for S =0.3and 0.5based on HMM.The ampli-tude of the modeled signals scales approximately linearly with variations in S .Increasing either G to 1.2or n 2to 100result in increased model signal amplitude of about 50%.Only small changes in frequency or phase occur.Two dif-ferences to the model of Elosegui et al.[1995]can be identified.First,the signal in HMM is substantially reduced at high elevations,which is in general agreement with the pattern seen in GPS carrier phase residuals.Second,both amplitude and frequency of the HMM is proportional to H ,whereas the Elosegui et al.[1995]model does not show the same sensitivity of amplitude to variations in H (compare Figure 1,left versus right).2.2.Simulation Approach[17]Our GPS simulator is based on the undifferenced GPS observable,and is conceptually similar to that of Santerre [1991].Observation ‐level biases,such as d L LC ,are entered via the “observed minus computed ”term (b )of the batch least squares adjustment:^x ¼A T WA ÀÁÀ1A T Wbð4Þ[18]The design matrix,A ,is defined by the partialderivatives of the functional model with respect to the parameters.The effect of the unmodeled signal on theseparameters is reflected in the estimated values ^x .W is the inverse of the observation variance ‐covariance matrix.[19]Initial station coordinates are taken from the ITRF2005coordinate set and satellite positions are taken from one of three orbit configurations (section 2.3).Satellite orbits and clocks are assumed known and fixed.Unless otherwise specified below,estimated parameters are the corrections to initial station coordinates,tropospheric zenith delays,receiver clocks (normally every epoch)and realvalued ambiguity terms (normally one per satellite pass).In these simulations,nonzero values of the estimated parameters represent parameter bias.Correct integer ambiguity fixing may be simulated by simply removing these terms from the design matrix [Santerre ,1991].[20]This simulator has previously been used by King et al.[2003]to study propagation of tidal signals in sub-daily coordinate estimates;the observed biases in output time series were accurately reproduced in the simulator.We have also verified the simulator by reproducing the propa-gated periodic biases observed in the GIPSY solutions of Penna et al.[2007]to within very small errors.We therefore assume the simulator is capable of reproducing the effects of systematic errors on real GPS solutions (that use an undifferenced observation strategy),but with the advantage of controlling all systematic error sources.[21]For the tests described here,we used a typical 24h “observation ”session and estimated adjustments to topo-centric station coordinates (north,east and up)once per day (i.e.,once per session),tropospheric zenith delay parameters once per hour,and used an elevation cutoff angle of 7°.By default we applied uniform weighting to all observations and include a single real value ambiguity parameter per satellite pass (we assess the impact of elevation ‐dependent weighting and ambiguity fixing throughout section 3).We used one measurement epoch every 300s (to reduce the computational burden)and considered data over the years 2000–2007inclusive for a sample of 20sites (Figure 2)in the International GNSS Service (IGS)[Dow et al.,2005].[22]By fixing the satellite orbits,clocks and earth orien-tation parameters to predetermined values we are potentially oversimplifying the problem.However,since multipath isFigure 2.Site locations from the IGS network used in this study.KING AND WATSON:MULTIPATH AND GEOMETRY EFFECTS ON GPS B04403B044034of 23heights above reflectors and reflector conditions are all site specific)they are unlikely to systematically bias parameters with large spatial scales,and hence we argue that a site ‐by ‐site analysis is reasonable.This remains to be verified in further work.[23]Our simulations represent a substantial advance on the work of Elosegui et al.[1995],which was limited in part by the available computational power at the time.First,they performed a simplified adjustment,considering mainly a one ‐dimensional (vertical)coordinate with,at most,one tropospheric zenith delay term per day and they did not examine the effects of ambiguity fixing.Second,they report on simulations for only a small number of (noncontinuous)days.Third,they reported on the propagation at only a single midlatitude site.Fourth,they used a multipath model not entirely appropriate to the near field.Each of these dif-ferences affects the least squares design matrix (or b in the last case),and hence could alter the propagation into long ‐term GPS time series.2.3.Satellite Orbit Configurations2.3.1.Clear Horizon:Constant Constellation[24]In order to provide a non time variable reference orbit,we adopted an artificial configuration that used a fixed 24satellite constellation,each with a fixed orbit repeat period of 24h minus 246s,close to the average GPS satellite orbital repeat time [Agnew and Larson ,2007].To achieve this constellation,we adapted the “perfect GPS orbit ”scenario as developed in a simulator implemented by Penna and Stewart [2003].The horizon at each site was assumed clear for this configuration;that is,satellites are observed without ob-struction down to the elevation cutoff angle of 7°.2.3.2.Clear Horizon:Evolving Constellation[25]To investigate the propagation impacts of a more realistic time variable orbit in our simulations,this “evolving constellation ”configuration adopted orbits from the daily broadcast ephemerides,with satellites set as unhealthy eliminated from the simulations.Again,this configuration assumed no obstructions above the elevation mask at each site.[26]The time variability of this configuration can be clearly seen in Figure 3(blue)where we show constellation statistics as a function of elevation over time.The minimum,maximum and standard deviation of epoch by epoch satellite elevations (computed in daily bins)are shown for a repre-sentative set of sites.Changes in the blue lines reflect the changing constellation geometry over time.The mini-mum elevation angle is governed by the 7°elevation cut-off used in the simulations.The maximum elevation angle and standard deviation of all elevation angles are governed by the actual satellite constellation as observed from each site location.[27]The temporal variability of the satellite geometry in Figure 3is striking.MAW1exhibits a strong secular term in maximum satellite elevation over time,although this is a feature of all high ‐latitude sites to some extent.More equatorial sites exhibit high ‐frequency variation in maxi-mum elevation and low ‐frequency fluctuations in elevation standard deviation.A clear trend in elevation standard de-viation between 2000and 2002is also a common feature to many sites.2.3.3.Obstructed Horizon:Evolving Constellation [28]The final orbit configuration assessed within the simulations takes into consideration time variable changes that occur due to the influence of local tracking issues,hardware changes and site obstructions above the elevation cutoff angle that are also potentially time variable and highly site specific.We derived this constellation by using only those satellite observations that are used in analyses of real world GPS data in a conventional GIPSY PPP analysis [Webb and Zumberge ,1995;Zumberge et al.,1997].Con-stellation statistics from this constellation (shown in brown,Figure 3)show considerable variation from the clear hori-zon,constant constellation configuration discussed previ-ously.Notable differences are observed at sites such as MCM4and DUBO which exhibit both secular and clear quasi ‐periodic characteristics.3.Simulation Output3.1.Clear Horizon:Constant Versus Evolving Constellation[29]Figure 4shows the simulation output highlighting the propagation of the HMM d L LC into the height compo-nent of three representative sites using H =0.1m,H =0.2m,and H =1.5m,for both the ambiguity free and fixed scenarios.The effect of a time ‐varying constellation may be seen by comparing the constant and evolving constellation scenarios (Figures 4(left)and 4(right),respectively).The three sites are NTUS,an equatorial site;POTS,a midlatitude site;and MCM4,a high ‐latitude site.Summary statistics including the offset,slope and RMS (white noise)are pro-vided for all sites in Table 1.[30]On first inspection,the most noticeable difference between these simulations is a clear shift from a stationary time series with high ‐frequency periodic variability for the constant constellation,toward clear low ‐frequency vari-ability present within the evolving constellation output.Also present in the later output are occasional transient events.For example,the H =1.5m NTUS ambiguity fixed example (Figure 4)shows what could be interpreted as a significant offset in the coordinate time series during late 2000.Closer examination of the time series shows that the offset is ∼1mm,and occurs over no more than 2–3days,and pos-sibly as quickly as from one day to the next.This offset is purely an artifact of the propagation of the systematic error introduced into the simulations as a function of the time variable satellite constellation.[31]In relation to the north and east coordinate compo-nents,we observe a similar pattern of variability yet ap-proximately an order of magnitude smaller in magnitude.This finding agrees with intuition given the simulated multipath signal is azimuthally symmetrical and hence one would expect the effects on north and east components to be relatively small.In the main,we show below only Figures 4–11pertaining to the height component,including the results for north and east components in the supple-mentary material where warranted.[32]Returning to the vertical component,and now con-sidering the height bias (offset in Table 1),we observe biases reaching just over 7mm for all tested values of H ,and note that the offset is approximately equal for the constant and evolving constellation cases.Biases for H =0.2m tendMULTIPATH AND GEOMETRY EFFECTS ON GPS B044035of 23to be smaller,but the mean bias will change depending on elevation cutoff angle (see below).Table 1confirms the output for the constant constellation has a zero trend com-puted over the entire period (2000.0–2008.0).The evolving constellation case shows trends reaching ±0.16mm yr −1insome instances;the effect over shorter periods could be sub-stantially larger,as is suggested by Figure 4,and it will also scale with input multipath amplitude.[33]Considering next the variability of the simulation output,(RMS in Table 1),we observe a progressiveincreaseFigure 3.Daily elevation angle statistics generated using the broadcast constellation (blue)and those observations actually used in a GIPSY PPP analysis (brown).Units are degrees.Note the different scales for each plot.KING AND WATSON:MULTIPATH AND GEOMETRY EFFECTS ON GPS B04403B044036of 23in scatter from H =0.1m to H =1.5m,and from constant to evolving constellations (mean values of 0.01,0.07and 0.15mm for the constant case,and 0.04,0.21and 0.49mm for the evolving case,H =0.1,0.2,and 1.5,respectively).The RMS shows a small yet interesting correlation with latitude for the evolving constellation case,with the maxi-mum RMS present near the equator,reducing to a minimum at approximately ±50°,and subsequently increasing toward the poles.This pattern is expressed across all values of H ,increasing significantly from H =0.1to H =1.5.[34]The difference between the ambiguity free and fixed cases is interesting for both the constant and evolving constellation scenarios.In the time domain (Figure 4),there appears to be a clear reduction in the energy of the periodic components within the time series when moving from the ambiguity free to fixed cases.To assist in the analysis of these periodic components and potentially time correlated noise structures,we compute global stacks of power spectra using the Lomb ‐Scargle periodogram [Scargle ,1982]as implemented according to Press et al.[1992]with an over-sampling factor of 4.We repeated the analysis with an oversampling factor of 1and found noin the expression of various harmonic peaks present in the spectra.In order to aid comparison between different simulations,prior to stacking in the frequency domain,the power spectra for each time series are normalized by an arbitrary variance of 1mm 2for each coordinate component.We generate our stacked spectra by computing the median normalized power estimate across each frequency.[35]The stacked spectra for the constant constellation (Figure 5,left)confirm that these time series are composed of a stationary series with a complex harmonic comb of energy superimposed.The energy within this harmonic comb is maximum for the H =0.2m case,and a minimum for the H =0.1m scenario.It is interesting that dominant peaks occur at harmonics of a period close to one year.On closer inspection,these harmonics are in fact multiples of 351.4days,equivalent to the so ‐called GPS satellite draconitic year (abbreviated here as dy)which defines the average repeat period of the GPS satellites in inertial space relative to the sun.In a study of stacked spectra taken from the weekly solutions of the IGS,Ray et al.[2008]noticedFigure 4.Height bias time series for three sites when propagating d L LC with H =0.1m (gray/black),H =0.2m (blue)and H =1.5m (magenta)for (left)constant constellation and (right)evolving constellation.Colors match those in Figure 1.Ambiguity ‐free (lighter shades)and ambiguity ‐fixed (darker shades)solutions are shown.KING AND WATSON:MULTIPATH AND GEOMETRY EFFECTS ON GPS B04403B044037of 23。

郑州市2023 年高中毕业年级第二次质量预测英语试题卷本试卷分四部分，考试时间120 分钟，满分150 分（听力成绩算作参考分）。

考生应首先阅读答题卡上的文字信息，然后在答题卡上作答，在试题卷上作答无效。

第二部分阅读理解（共两节，满分40 分）第一节（共15 小题；每小题2 分，满分30 分）阅读下列短文，从每题所给的A、B、C 和D 四个选项中，选出最佳选项，并在答题卡上将该项涂黑。

AHigh school programs at the National Gallery of Art value depth over breadth, exploring original works of art through a single specific question or theme.Studio WorkshopsSingle museum visit, 2.5 hoursGrades 9-12These half-day art workshops include an in-depth examination and discussion of works of art in the galleries, followed by behind-the-scenes access to the Education Studio, where students create a related art project.National Gallery of Art educators will encourage students to look carefully at works of art and then share their responses and come up with theories based on their observations.Students will have the chance to create a work of art in the studio inspired by what they have seen in the galleries.Museum MakersExploring Art and MuseumsGrades 11-12The Museum Makers program explains how museums operate and what they have to offer. It gives upper-level high school students the tools to experience, understandand interpret art. Participants will gain an insider's view of how an art museum works.Students meet for seven Saturday sessions from 10:00 a.m. to 3:00 p.m. Completion of the program requires attendance of all seven sessions.Creative WritingGrades 7-12, 90 minutesStudents will provide a voice for their personal responses to art through creative writing while they are looking at a selection of artworks in the galleries. Using close observation, group discussion and personal reflection, they will be guided through exercises that use different writing forms, including free-form poetry.A maximum of 30 students ( minimum of 15) will be accepted at each session.21.What can students do at Studio Workshops?A.Get basic training as an artist.B.Put forward their own art theories.C.Discuss with artists about their works.D.Learn about artists, inspiration for their works.22.What can students get from Museum Makers?A.Methods of how artworks are created.B.Experience in running an art museum.C.Knowledge about how an art museum works.D.Academic credits for completing the program.23.Which group can attend Creative Writing at a session?A.15 college students.B. 10 Grade 9 students.C. 25 Grade 10 students.D. 40 high school students.BI never imagined that someone telling me I looked skinny would anger me. And yet, I was made very angry when a colleague pinched （捏）my waist and screamed, “Rosa, you've lost weight. You look great In The truth is that I was tired and not taking care of myself. I decided to start a proper weight-loss program.The first to go would be road rage （路怒）.I am in far less control of this weight than any other. Every time something gets in my path, I fly off the handle. I need to lose the road rage, and fast! No, no more speed. Instead, I now repeat the words："I am not in a hurry. " This year, I will drive safely, allowing "stupid" to happen all aroundme. From that, I hope to gain patience.Next is guilt. When guilt drives my conscience to do better, it's functional. But when it presents itself as an internal dialogue that goes nowhere, it's useless. This year, I want to stop feeling guilty for not keeping a cleaner house, for spending time away from my children to be with friends, for not attending every party because I’d rather be at home, or for watching TV when I should be reading. My image and performance are not at the front of anyone else’s mind but my own. From this, I hope to gain freedom to be myself.The last is fear. Fear has held me back. Fear of failure has prevented me from being a writer. Fear of embarrassment has prevented me from giving an opinion. Fear of rejection has stopped me from aiming higher in my life. Fear of regret has led me into situations that made me uncomfortable. If I can lose any one of these fears, I stand to gain experience.So, if I can lose the rage, shake off some guilt, and take fear off my plate, I stand to gain patience, freedom, and experience. Pound for pound I have not lost a thing but I will be much lighter. Next time, I hope my colleague looks me in the eye to see my glow instead of pinching part of me that has nothing to do with how great I really look.24.What does the underlined part “fly off the handle” in paragraph 2 probably mean?A.Pick up speed.B. Drive off.C. Feel quite nervous.D. Become very angry.25.What has made the author feel guilty before?A.Attending too many parties.B.Reading much with her children.C.Wasting her time in watching TV.D.Spending little time with her friends.26.How has fear affected the author?A.It has prevented her achieving her goals.B.It has stopped her furthering her education.C.It has made it difficult for her to make friends.D.It has caused her to quit her dream of being a teacher.27.What does the author expect to gain from her weight-loss program?A.Respect.B. Independence.C. Optimism.D. Tolerance.CSix months before she died, my grandmother moved into an old people's home and I visited her there. The room was clean and warm, and the care assistants were kind and cheerful. A general knowledge quiz show was on the television, and the only other sound was snoring （打呼噜）.People moved only when they needed to be helped to the bathroom. It was disappointing. Grandmother talked a lot about how much she missed seeing her grandchildren, but I knew from my sister that they hated going to visit her there.So I was interested to read a newspaper article about a new concept in old people's homes in France. The idea is simple, but revolutionary - combining a residential home for the elderly with a nursery school in the same building. The children and the residents eat lunch together and share activities. In the afternoons, the residents enjoy reading or telling stories to the children, and if a child is feeling sad or tired, there is always a kind lap to sit on.The advantages are huge for everyone concerned. The children are happy, because they get a lot more individual attention. The residents are happy because they feel useful and needed. And the staff are happy because they see an improvement in the physical and psychological health of the residents and have an army of assistants to help with the children.Nowadays there is less and less contact between the old and the young in an increasing number of countries. There are many reasons for this, including the breakdown of the extended family, working parents with no time to care for ageing relations, families that have moved away, and smaller flats with no room for grandparents. But the result is the same - increasing numbers of children without grandparents and old people who have no contact with children, and more old people who are lonely and feel useless, along with more and more families with young children who desperately need more support. Ifs a major problem in many societies.That's why intergenerational programs, designed to bring the old and the young together, are growing in popularity all over the world.28.What does the underlined word "residents" in paragraph 2 probably refer to?A.Old people.B. School teachers.C. Assistants.D. Staff.29.How were the old people at the home the author's grandmother was in?A.They felt lonely and useless.B.They weren't allowed to be visited.C.They weren't looked after properly.D.They lived in a dirty and uncomfortable room.30.What does the author think is a major problem in many societies today?A.The extended family is broken down.B.There isn't much room for grandparents.C.Working parents have no time to care for their children.D.There isn't much contact between the old and the young.31.What will be probably talked about later in the passage?A.Advice on how to communicate with children.B.Plans for setting up more homes for old people,C.Examples of successful intergenerational programs.D.Ways of teaching entertainment skills to old people.DMicroplastic pollution is increasing greatly around the globe, according to a study of plastic particles （微粒）carried in the air.People are already known to breathe, drink and eat microplastics, and research suggests that pollution levels will continue to rise rapidly. The researchers said that breathing in these particles can be harmful to lung tissue and lead to serious diseases.Professor Natalie Mahowald, at Cornell University in the US and part of the research team, said, " But maybe we could solve this before it becomes a huge problem, if we manage our plastics better, before they accumulate in the environment and move around everywhere."The research, published in the journal Proceedings of the National Acadenry of Sciences, examined airborne （空气传播的）microplastics, which have been far less studied than plastics in oceans and rivers.The team gathered more than 300 samples of airborne microplastics from 11 s ites across the western US. These were the basis for atmospheric modeling that estimated the contribution from different sources （来源）,and it was the first such study to do so.They found that roads were the main factor （因素）in the western US, linked to about 85% of the microplastics in the air. These are likely to include particles from tiresand brake pads on vehicles, and plastics from litter that had been broken down.The researchers extended their modeling work to a global level and this suggested that while roads are also likely to be the major driver of airborne plastics in Europe, South America and Australia, plastic particles blown up from fields may be a much bigger factor in Africa and Asia.Professor Andreas Stohl of the University of Vienna's Faculty of Earth Sciences said, “The study confirms the global-scale （全球规模的）nature of microplastic transport in the atmosphere and does a good job in highlighting highly relevant and concerning possibilities, but more measurement data is needed to get a better idea of the sources.”32.What can be known about microplastic pollution from this text?A.The particles can do great harm to our lungs.B.Airborne microplastics have been widely studied.C.It has become the most pressing environmental problem.D.There is less plastic in the air than in oceans and rivers.33.What did the researchers find out about microplastic pollution?A.Its results differ across many continents.B.Africa and Asia are suffering most from it.C.Roads and fields are largely to blame for it.D.It spreads fast from one continent to another.34.What should the researchers do next according to Professor Andreas Stohl?A.To predict the potential damage of microplastics.B.To understand the nature of microplastic pollution.C.To improve the method of collecting samples of microplastics.D.To collect more data to understand the sources of microplastics.35.What can be the best title for this text?A.Effects of microplastics on human healthB.Microplastic pollution on the global scaleC.Possible solutions to microplastic pollutionD.Microplastic pollution rising quickly in the air第二节（共5 小题；每小题2 分，满分10 分）根据短文内容，从短文后的选项中选出能填入空白处的最佳选项,并在答题卡上将该项涂黑。

在核心期刊发表的英文Publishing in core journals is a significant achievement for researchers and scholars. It not only enhances their academic reputation but also contributes to the advancement of knowledge in their respective fields. In this document, we will discuss the importance of publishing in core journals and provide some practical tips for achieving this goal.First and foremost, publishing in core journals allows researchers to reach a wider audience and have a greater impact on their field of study. Core journals are highly regarded within the academic community and are often the first choice for scholars seeking high-quality research articles. By publishing in these journals, researchers can ensure that their work is read and cited by other experts in their field, thereby increasing their visibility and influence.Furthermore, publishing in core journals is a mark of academic excellence. It demonstrates that the research has undergone rigorous peer review and has been deemed to be of high quality and significance. This can enhance the researcher's reputation and credibility within the academic community, leading to increased opportunities for collaboration, funding, and career advancement.In order to publish in core journals, researchers must adhere to high standards of scholarship and research integrity. This includes conducting original and rigorous research, presenting their findings clearly and concisely, and adhering to ethical guidelines and best practices in their field. Additionally, researchers must be familiar with the specific requirements and preferences of the core journals they are targeting, such as formatting guidelines, citation styles, and submission processes.To increase the likelihood of publishing in core journals, researchers should carefully select the journals to which they submit their work. It is important to target journals that are well-regarded in the researcher's field and have a high impact factor. Researchers should also consider the scope and focus of the journal, ensuring that their work aligns with the journal's editorial priorities and audience.In addition, researchers should pay close attention to the feedback and suggestions provided by peer reviewers and editors. Constructive criticism and guidance from experts in the field can help researchers improve their work and increase its chances of acceptance in core journals. Researchers should be open to revising and refining their work based on the feedback received, demonstrating their commitment to producinghigh-quality research.In conclusion, publishing in core journals is a significant achievement for researchers and scholars. It provides an opportunity to reach a wider audience, enhance academic reputation, and contribute to the advancement of knowledge in their field. By adhering to high standards of scholarship and research integrity, carefully selecting target journals, and responding to feedback from peer reviewers and editors, researchers can increase their chances of publishing in core journals and making a meaningful impact in their field.。

advances in earth sciences影响因子Advances in Earth Sciences (AES) is a reputable, peer-reviewed journal that publishes high-quality research articles spanning various topics in the field of Earth sciences. As the advancement of Earth sciences are crucial for a better understanding of our planet and addressing the challenges it faces, the impact factor of AES plays a significant role in determining the influence and reach of the journal. In this article, we will delve into the factors that contribute to the impact factor of AES, starting from its inception to the present day.The impact factor of a scientific journal is a measure of the average number of citations received per article published in that journal within a specific time period. It offers a quantitative assessment of the quality and influence of a journal within its field. For AES, the impact factor is a reflection of the importance and significance of the research articles it publishes, as well as the wide readership and citation rate it attracts.In the early years of AES, the impact factor was relatively low as the journal was still in its infancy. However, over time, with the increasing recognition and credibility of the journal, the impactfactor experienced a steady rise. This can be attributed to various factors, which we will now explore in more detail.Firstly, the quality of the research articles published in AES is a crucial determinant of its impact factor. The journal follows a rigorous peer-review process, ensuring that only high-quality and groundbreaking research is accepted for publication. By maintaining high standards, AES attracts renowned scientists and researchers to submit their work, thereby increasing the overall caliber and impact of the journal.Secondly, the relevance and timeliness of the research topics covered in AES also contribute to its impact factor. As the field of Earth sciences constantly evolves and addresses emerging global challenges, AES strives to publish cutting-edge research in areas such as climate change, natural disasters, geological processes, and environmental management. By focusing on these pressing issues, AES attracts the attention of researchers, policymakers, and other scientists who actively cite the published articles, thereby increasing the impact factor.Furthermore, the accessibility and international reach of the journalplay a vital role in determining its impact. AES aims to ensure that its publications are widely available and easily accessible to the global scientific community. By utilizing online platforms and open-access options, AES maximizes the visibility and dissemination of its articles. This broad accessibility increases the chances of articles being cited by researchers from various disciplines and geographical locations, positively influencing the impact factor.Another factor that enhances the impact factor of AES is its commitment to fostering collaborations and interdisciplinary research. Earth sciences inherently encompass a wide range of disciplines like geology, geography, atmospheric sciences, and hydrology. By encouraging interdisciplinary approaches and publishing articles that bridge different fields, AES attracts a diverse readership and consequently increases the likelihood of citations, thereby raising its impact factor.Lastly, the reputation and standing of the editorial board and reviewers of AES contribute significantly to its impact factor. AES is comprised of renowned scientists and experts in the field, who bring their expertise and knowledge to the review and selectionprocess. The reputation of the editorial board as well as the stringent review process assures the scientific community of the reliability and credibility of the articles published in AES. This confidence leads to higher citations and ultimately increases the impact factor of the journal.In conclusion, the impact factor of Advances in Earth Sciences (AES) is influenced by various factors that contribute to its recognition and influence within the scientific community. These factors include the quality of research articles, the relevance of the topics covered, the accessibility and reach of the journal, its interdisciplinary approach, and the reputation of the editorial board and reviewers. By continuously nurturing these factors, AES maintains a high impact factor, thereby promoting the advancement and dissemination of knowledge in the field of Earth sciences.。

Distribution of sulfur and pyrite in coal seams from Kutai Basin(East Kalimantan,Indonesia):Implications for paleoenvironmental conditionsSri Widodo a ,⁎,Wolfgang Oschmann b ,Achim Bechtel c ,Reinhard F.Sachsenhofer c ,Komang Anggayana d ,Wilhelm Puettmann eaDepartment of Mining Engineering,Moslem University of Indonesia,Jln.Urip Sumoharjo,Makassar,Indonesia bInstitute of Geosciece,J.W.Goethe-University,Altenhöferallee 1,D-60438Frankfurt a.M.,Germany cDepartment of Applied Geoscience and Geophysics,University of Leoben,Peter-Tunner-Str.5,A-8700Leoben,Austria dDepartment of Mining Engineering,Bandung Institute of Technology,Jln.Ganesa 10,I-40132Bandung,Indonesia eInstitute of Atmospheric and Environmental Sciences,Dapartment of Analytical Enviromental Chemistry,J.W.Goethe-University,Altenhöferallee 1,D-60438Frankfurt a.M.,Germanya b s t r a c ta r t i c l e i n f o Article history:Received 12August 2009Received in revised form 29November 2009Accepted 3December 2009Available online 13December 2009Keywords:Kutai Basin Pyrite SulfurFramboidal Ombrogenous TopogenousThirteen Miocene coal samples from three active open pit and underground coal mines in the Kutai Basin (East Kalimantan,Indonesia)were collected.According to our microscopical and geochemical investigations,coal samples from Sebulu and Centra Busang coal mines yield high sulfur and pyrite contents as compared to the Embalut coal mine.The latter being characterized by very low sulfur (b 1%)and pyrite contents.The ash,mineral,total sulfur,iron (Fe)and pyrite contents of most of the coal samples from the Sebulu and Centra Busang coal mines are high and positively related in these samples.Low contents of ash,mineral,total sulfur,iron (Fe)and pyrite have been found only in sample TNT-32from Centra Busang coal mine.Pyrite was the only sulfur form that we could recognize under re flected light microscope (oil immersion).Pyrite occurred in the coal as framboidal,euhedral,massive,anhedral and epigenetic pyrite in cleats/fractures.High concentration of pyrite argues for the availability of iron (Fe)in the coal samples.Most coal samples from the Embalut coal mine show lower sulfur (b 1wt.%)and pyrite contents as found within Centra Busang and Sebulu coals.One exception is the coal sample KTD-38from Embalut mine with total sulfur content of 1.41wt.%.The rich ash,mineral,sulfur and pyrite contents of coals in the Kutai Basin (especially Centra Busang and Sebulu coals)can be related to the volcanic activity (Nyaan volcanic)during Tertiary whereby aeolian material was transported to the mire during or after the peati fication process.Moreover,the adjacent early Tertiary deep marine sediment,ma fic igneous rocks and melange in the center of Kalimantan Island might have provided mineral to the coal by uplift and erosion.The inorganic matter in the mire might also originate from the ground and surface water from the highland of central Kalimantan.©2009Elsevier B.V.All rights reserved.1.IntroductionMost of the inorganic matter in coal is present as minerals which are dispersed throughout the coal macerals.Individual grains of minerals vary largely in size from less than one micrometre to tens or hundreds of micrometres.Sometimes mineral-rich layers are even thick enough to be visible on the coal surface (Taylor et al.,1998).Mineral components in the coals were classi fied in three groups according to their origin (Stach et al.,1975):(1)Mineral from the original plants;(2)mineral that formed during the first stage of the coali fication process or which was introduced by water and wind into the later coal deposits;and (3)mineral deposited during the second phase of the coali fication process,after consolidation of the coal,byascending or descending solutions in cracks,fissures,or cavities or by alteration of primarily deposited minerals.The dominant mineral of coals is usually composed of sul fides,clay,carbonates,and quartz and sometimes additional phosphates,heavy minerals,and salts as minor contributions to inorganic matter of coal.In most coals,sul fides are preferentially composed of pyrite and marcasite but pyrite is in general dominating by far (Balme,1956;Mackowsky,1943).Sul fides can be categorized as either syngenetic (primary),early-diagenetic or epigenetic (secondary)in origin.During peati fication,syngenetic or early-diagenetic fine-crystalline or fine-concretionary pyrite appears,commonly in the form of framboids.Syngenetic pyrite formed during accumulation of the peat and/or during early (humi fication)processes,and is usually small in size,and intimately dispersed throughout the coal (Renton and Cecil,1979;Reyes-Navarro and Davis,1976).Occasionally,the cell walls of plant material have been replaced by pyrite (Taylor et al.,1998).Falcon and Snyman (1986)suggest that the accumulation of pyrite in coal might also ariseInternational Journal of Coal Geology 81(2010)151–162⁎Corresponding author.Tel.:+62411454775;fax:+62411453009.E-mail address:srwd007@ (S.Widodo).0166-5162/$–see front matter ©2009Elsevier B.V.All rights reserved.doi:10.1016/j.coal.2009.12.003Contents lists available at ScienceDirectInternational Journal of Coal Geologyj o u r n a l ho m e p a g e :w w w.e l s ev i e r.c o m /l o c a t e /i j c o a l g e ofrom the aeolian andfluviatile import of iron-rich mineral at the time of peat accumulation followed by in-situ precipitation.Epigenetic pyrite is incorporated in the coal after compaction or partial consolidation(Reyes-Navarro and Davis,1976)and is generally much larger(coarse grained)andfills cracks,cleats,and cavities (Renton and Cecil,1979).The formation of epigenetic pyrite is dependent primarily on the availability of reduced sulfur,dissolved cation(ferrous iron)and a suitable site for formation i.e.,cleat (Casagrande et al.,1977;Spears and Caswell,1986;Demchuk,1992). Moreover,epigenetic pyrite might be precipitated from water percolating into fractures,cavities and pores present in coal seams long after accumulation of the peat(Falcon and Snyman,1986).In general,coals deposited in paralic basins contain more pyrite than those in limnic basins.Among the paralic deposits,coal seams which have been influenced by marine transgressions are consistently characterized by a particularly high content of pyrite and sometimes also of organic sulfur,especially in the upper part of the seams(Balme, 1956;Dai et al.,2002;Mackowsky,1943).In sulfur-rich humic coals, pyrite in the form offine grains orfine concretions is particularly common in microlithotypes containing a high proportion of vitrinite; these forms also tend to be common in sapropelic coals.In the absence of other criteria(such as marine fossils or coal balls),a relatively high proportion of synsedimentary or early-diagenetic pyrite can be useful for seam correlation.Many previous investigations(Anggayana et al.,2003;Baruah,1995; Dai et al.,2002,2003,2006,2007,2008;Dai and Chou,2007;Elswick et al.,2007;Frankie and Hower,1987;Kortenski and Kostova,1996; Lόpez-Buendía et al.,2007;Querol et al.,1989;Renton and Bird,1991; Strauss and Schieber,1989;Turner and Richardson,2004;Wiese and Fyfe,1986)have described the characteristics,type,morphology, genesis,and distribution of pyrite in coal seams from different deposits. Our investigation deals with sulfur and pyrite occurrences in the Miocene coal seams from Centra Busang,Sebulu and Embalut coal mines,Kutai Basins,East Kalimantan,Indonesia.The primary purpose of the study is to explain why most Miocene coal seams from Kutai Basin have very low sulfur contents,whereas in some coal seams higher sulfur contents are observed.The second purpose is to identify the types of pyrite and factors affecting their appearance and it's relation with paleoenvironmental conditions during deposition of the coals.2.Geological settingKalimantan is surrounded by marginal basins of South China,Celebes and Sulu seas,microcontinental fragments of south China in the north,and mainland SE Asia(Indochina and peninsular Malaysia)in the west(Moss and Chambers,1999).Kalimantan was interpreted as the product of Mesozoic accretion of oceanic crustal material(ophiolite),marginal basin fill,island arc material and microcontinental fragments onto the Paleozoic continental core of the Schwaner Mountain in the SW of the island(Fig.1; Hall and Nichols,2002;Hutchison,1989;Moss and Wilson,1998;Widodo et al.,2009).During early Tertiary times,Kalimantan formed a promontory of the Sundaland Craton:the stable eastern margin of the Eurasian plate (Hall,1996;Metcalfe,1998).In the east,Kalimantan is separated from Sulawesi by the deep Makassar Basins(Fig.1),formed during Paleogene times(Situmorang,1982).The main areas of eastern, central and northern part of Kalimantan are coated by Tertiary sediments(Fig.1)which were deposited influvial,marginal-marine or marine environments.Tertiary sedimentation in these areas occurred at the same time with,and subsequent to,a period of widespread Paleogene extension and subsidence,which may have commenced in the middle Eocene or earlier(Moss and Wilson,1998).A number of Tertiary sedimentary basins,of which the Kutai Basin is the largest,are identified across Kalimantan(Moss et al.,1997).The island of Kalimantan and in particular the Kutai Basin has experienced a complex tectonic history from the Paleogene to the present day.The Kutai Basin was formed during early Tertiary times and wasfilled-up with clastic sediments progressing from the western to the eastern part of the basin.This basin was subdivided into the Upper Kutai Basin,consisting of Paleogene outcrops with Cenozoic volcanics possessing a strong northwest–southeast struc-tural grain,and the Lower Kutai Basin with Miocene strata cropping out in a north–northeast-trending structure.The Meratus Mountains to the southwest and the Central Kalimantan Mountains to the north of the Kutai Basin have an ophiolitic basement together with Paleogene strata striking dominantly in a north–northeast direction (Clay et al.,2000).The coal mining companies are located in the vicinity of the Mahakam River,Kutai Basin,East Kalimantan Province(Fig.2).The precise geographic position of Sebulu coal mine is S00°26′40.4″/E116°52′54.1″and Centra Busang coal mine is S00°44′22.2″/E116°89′16.6″,whereas the Embalut coal mine is situated S00°33′34.9″/E117°12′15.5″.Centra Busang is located in the Busang village,East Kutai regency and Sebulu coal mine in the Sebulu village,Kutai Kertanegara regency,East Kalimantan province. The Embalut coal mine is located in Embalut village,Kutai Kertanegara regency,East Kalimantan province.Coal seams in the Centra Busang and Sebulu mines were found in the Pulau Balang Formation with Middle Miocene age,and coal seams in the Embalut mine was found in the Pulau Balang(Middle Miocene age)and Balikpapan Formation with Upper Miocene age(Fig.3).Previous studies of the sedimentary evolution of the Kutai Basin, based onfield survey and oil wells,have shown that the Tertiary sequences are broadly regressive in general with a(dominantly) offshore marine argillaceous sequence of Palaeocene age followed by a coal bearing deltaic and coastal plain succession of Miocene age. Shoreline progradation was generally towards the east(Samuel and Muchsin,1976;Rose and Hartono,1978in Land and Jones,1987).According to Supriatna and Rustandi(1986)the Neogene succession in the Kutai Basin includes from bottom to top the following formations:Pamaluan,Bebuluh,Pulau Balang,Balikpapan, Kampung Baru Formation and alluvial.The Pamaluan Formation(up to1500m thick)consists of sandstones with insertion of claystone, shale,limestones,and siltstone.It formed in a deep marine environment during Late Oligocene and Early Miocene times.The Lower Miocene Bebuluh Formation(up to900m thick)consists of limestones with insertion of sandy limestones and argillaceous shales.The deposition of the formation occurred in a shallow sea.The Bebuluh Formation interfingers with the Pamaluan Formation.The Pulau Balang Formation of Early to Middle Miocene age overlies the Bebuluh Beds concordantly. It is composed of graywackes,quartz sandstones,limestones,claystones, dacitic tuff and coal insertion.The thickness of coal seams ranges from 3to4m.The depositional environment can be characterized as deltaic to shallow marine according to Supriatna and Rustandi(1986).The formation is approximately900m thick.The Middle to Upper Miocene Balikpapan Formation(1000–1500m thick)uniformly overlies the Pulau Balang Formation and consists of quartz sandstone,clay with insertion of shale,and coal seams5to10m thick.The deposition of the Balikpapan Formation occurred in a delta environment.The Upper Miocene to Pliocene Kampung Baru Formation disconcordantly overlies the Balikpapan Formation.It is composed of quartz sandstone with insertion of clay,shale,silt and approximately3m thick coal(lignite). The deposition of the Kampung Baru Formation up to900m thick, sedimentary succession occurred in a delta.Alluvium deposit(alluvial) consists of sandy clay and clayey sands.3.Samples and methodCoal samples were collected in-situ with channel sampling method from three active surface mines in the Centra Busang(3samples),152S.Widodo et al./International Journal of Coal Geology81(2010)151–162Sebulu (2samples),and Embalut (8samples)coal mines,Kutai Basin,East Kalimantan,Indonesia.The sample preparation and microscopic examination generally followed the procedures described by Taylor et al.(1998).Coal particles of about 1mm in diameter were used for preparation of polished sections,which were embedded in a silicone mould (diameter 40mm)using epoxy resin as an embedding medium.After hardening,the samples were ground and polished.MicroscopicFig.1.Simpli fied geology of Kalimantan (modi fied from Moss and Wilson 1998;Hall and Nichols,2002).153S.Widodo et al./International Journal of Coal Geology 81(2010)151–162analyses were performed by a single-scan method with a Leica MPV microscope using re flected white and fluorescent light.At least 300points were counted for coal macerals and mineral.Pyrites were counted separately from the other minerals (for example,clay,carbonate,quartz)which were counted together in one group.Total sulfur contents were determined using an automated Leco SC-344carbon sulfur analyzer.A weighed coal sample is mixed with iron chips and a tungsten accelerator and is then combusted in an oxygen atmosphere at 1370°C.The moisture and dust are removed from the combustion product and the SO 2gas is measured by a solid-state infrared detector.Ash yields were determined following standard procedure DIN 51719using dry coal samples.One gram of each coal sample is heated 2h to 815°C (±15°C)in a muffel furnace,the residue was then cooled to room temperature and weighed.For trace element analyses,carried out by ACTLABS,Ancaster,Canada,the coal ash (0.5g)was dissolved in aqua regia (0.5ml H 2O,0.6ml concentrated HNO 3and 1.8ml concentrated HCl).After cooling,samples were diluted to 10ml with deionized water and homogenized.The digestion is near total for base metals,but will only be partial for silicates and oxides.The solutions were then analyzed using a Perkin Elmer OPTIMA 3000Radial ICP-MS for the 30elementsFig.2.Geographic map showing the locations of Sebulu,Centra Busang and Embalut coal mines in the Kutai Basin,East Kalimantan,Indonesia.Fig.3.Sedimentary sequences and the distribution of some fundamental parameters of the Embalut,Centra Busang and Sebulu coal field,Kutai Basin,East Kalimantan,Indonesia.154S.Widodo et al./International Journal of Coal Geology 81(2010)151–162suite.A series of USGS-geochemical standards were used as controls. The iron(Fe)is one of the elements to be discussed in this paper. 4.Results and discussion4.1.Ash,mineral,total sulfur and iron(Fe)contentsAsh yields,minerals,total sulfur,and Fe contents in the coal samples from Centra Busang,Sebulu and Embalut coal mines are summarized in Table1and cross-correlation are shown in Fig.4.The ash yield of the Centra Busang and Sebulu coals varies from1.40to 5.80(wt.%,db).The Embalut coal samples show higher variability in ash yields(1.33to8.98wt.%,db).Four coal samples from Embalut yield more than2wt.%(db)ash(Table1)while ash contents lower than2wt.%(db)are found in the samples KTD-36,KTD-35,KTD-43, and KTD-37(Table1).The ash contents of Cetra Busang and Sebulu coals show a positive correlation to the total sulfur+Fe(r2=0.83). Embalut coals show also a positive correlation between ash contents to the total sulfur+Fe(r2=0.77).The mineral contents of Centra Busang and Sebulu coals vary from 0.70to5.60(vol.%).Mineral is predominantly composed of pyrite.Clay and carbonates are also found in a significant quantity.Quartz is observed only in a trace proportion.In the coal samples from Centra Busang coal mine,mineral contents vary from3.70vol.%(TNT-30,seam BL-4)over1.60vol.%(TNT-31BL-7)to0.70vol.%(TNT-32,BL-7.1).The coal samples from Sebulu coal mine show mineral contents between 2.3vol.%(TNT-33)and5.6vol.%(TNT-34).The mineral contents of Centra Busang and Sebulu coals show a strong positive correlation to the ash contents(r2=0.96;Fig.4).Unlike to the Centra Busang and Sebulu coals,mineral in the Embalut coals is dominated by clay minerals. Carbonate,pyrite and quartz are found in small amounts.The mineral contents of Embalut coals vary from0.30to2.0(vol.%).Most of mineral contents are lower than2vol.%.The mineral contents(from micro-scopical analysis)of Embalut coal mine show a negative correlation to the ash contents in the coals(r2=0.05,Fig.5).The studied coal samples from the Centra Busang and Sebulu coal mines have relatively high total sulfur contents(up to3.15wt.%; Table1).Total sulfur contents show a positive correlation to the ash contents in the samples(r2=0.67;Fig.4).On the other hand,most samples from the Embalut coal mine show very low total sulfur contents(≤0.2wt.%).Sole exception is the coal sample KTD-38from Pulau Balang Formation with a total sulfur content of1.41wt.%.The correlation of total sulfur to the ash contents in the Embalut coal mine also shows a positive correlation(r2=0.84,Fig.5).Iron(Fe)contents in the samples from the Centra Busang and Sebulu coal mines fall within the range of0.17to1.51wt.%.As shown in Table1 and Fig.6,the iron(Fe)contents in the coal samples from Centra Busang and Sebulu coal mines show a strong positive correlation to the pyrite contents and total sulfur.The correlation coefficients are r2=0.96(Fe vs pyrite contents),and r2=0.86(Fe vs total sulfur).Whereas,iron(Fe) contents of Embalut coal samples are low and range from0.15to1.32%. Highest content are found in the sample KTD-38with a value of1.32%. Fig.7also shows a positive correlation of iron(Fe)contents to the pyrite contents and total sulfur in the coal samples from Embalut coal mine. The correlation coefficients are r2=0.97(Fe vs pyrite contents)and r2=0.99(Fe vs total sulfur).The sum of total sulfur and iron(Fe)is close to the amount of ash for Centra Busang and Sebulu coals(Table1).This indicates that a large proportion of the mineral in the coal samples must be composed of pyrite.In the two samples(TNT-30and TNT-33)the sum of the total sulfur content and the Fe content exceeds the ash content.In these samples some of the sulfur must be organically bond sulfur, which evaporates together with the organic matter during heating. The lowest total sulfur content(0.14wt.%)of the Centra Busang and Sebulu coal mines is observed in TNT-32,which provided a very low ash yield of1.40wt.%,db.This allows to estimate the non-pyritic mineral content to approximately1wt.%.4.2.Pyrite content and pyrite types in the coal seamsBased on microscopical analyses,the amount of pyrite in the Centra Busang and Sebulu coal samples varies from0.4to4.3vol.% (Table1).In comparison,most of pyrite contents of Embalut coal samples are lower than in Centra Busang and Sebulu coals and pyrite is only observed in three samples(KTD-36,KTD-43and KTD-38). Differences in the pyrite contents of coals from Centra Busang,Sebulu and Embalut coal mines are reflected by the type of pyrite found(i.e. framboidal,euhedral,massive,anhedral,and epigenetic/syngenetic pyrite in cleats and fractures).4.2.1.Framboidal pyriteFramboidal forms of pyrite are categorized as syngenetic(Dai et al., 2007).Some authors proposed that the type of this pyrite originates from pyritization of sulfur bacteria(Casagrande et al.,1977; Casagrande et al.,1980;Kortenski and Kostova,1996;Lόpez-Buendía et al.,2007;Querol et al.,1989;Renton and Cecil,1979).Kortenski and Kostova(1996)also proposed the possibility of pyritization of other kinds of bacteria which might have coexisted along with the sulfur metabolizing bacteria and supported the decomposition and assim-ilation of the plant tissue.Moreover,it has been suggested that framboidal pyrite might be generated from mineral solutions in inorganic material(Dai et al., 2002,2003;Kortenski and Kostova,1996).Other theories(Wilkin and Barnes,1997)suggested for the formation of framboidal pyrite is in first step the activity of biogenic processes i.e.,pyritic fossilization of bacterial colonies,and in a second step further growing of framboidalTable1Ash yield,minerals(from microscopical analysis),total sulfur,pyrite(from microscopical analysis)and iron(Fe)contents in the studied coal samples.Samples Seams Formations Coal mines Ash(wt.%,db)Mineral(vol.%)Total sulfur(wt.%,db)Pyrite(vol.%)Fe(wt.%)KTD-4221Balikpapan Embalut 2.66 1.30.050.00.18 KTD-3618 1.33 1.60.050.20.15 KTD-3517 1.650.30.060.00.21 KTD-4312 1.61 1.00.070.30.17 KTD-4010 5.050.70.200.00.20 KTD-399 2.81 1.00.100.00.22 KTD-388Pulau Balang8.98 1.0 1.410.7 1.32 KTD-377 1.77 2.00.180.00.20 TNT-30BL-4Pulau Balang Centra Busang 3.50 3.7 3.15 3.0 1.15 TNT-31BL-7.9 1.90 1.6 1.10 1.00.34 TNT-32BL-7.10 1.400.70.140.40.17 TNT-33ST Pulau Balang Sebulu 2.10 2.3 1.69 2.00.51 TNT-34STU 5.80 5.6 2.92 4.3 1.51155S.Widodo et al./International Journal of Coal Geology81(2010)151–162pyrite by organic processes,based on laboratory syntheses over a wide range of thermal conditions.Bacterial framboidal pyrite preserves the independence of the separate globules even when they form aggregates (Kortenski and Kostova,1996;Querol et al.,1989;Renton and Cecil,1979).During peati fication,syngenetic or early-diagenetic fine-crystal-line or fine-concretionary pyrite appears,commonly in the form of framboids.The Centra Busang and Sebulu coal samples contain bacterial framboidal pyrite in high abundance.An example is shown in sample TNT-34(Fig.8a).In some samples such as TNT-30from the Centra Busang coal mine the primary framboidal pyrite shows an overgrowth by secondary pyrite which is generally associated with clay minerals (Fig.8b).In most of the framboidal pyrite globules the crystals are densely intergrown and consist of some aggregates as previously described by Skripchenko and Berberian (1975;in Kortenski and Kostova,1996).Most of bacterial framboidal pyrite in the sample TNT-30appears as single bodies or solitary.In Embalut coal sample framboidal pyrite is not observed.4.2.2.Euhedral pyriteEuhedral pyrite is recognizable as well shaped pyrite crystals (Kortenski and Kostova,1996).Querol et al.(1989)described euhedral pyrite in the coal samples from Maestrazgo Basin,northeastern Spain.Kortenski and Kostova (1996)observed this type of pyrite in the coal samples from Bulgaria and divided euhedral pyrite into isolated and clustered varieties and isolated anhedral crystals and aggregates of euhedral crystals.Most of the euhedral pyrite is syngenetic and is generated during deposition of peat and/or during early humi fication.In general,the crystals of euhedral pyrite are small in size and intimately dispersed throughout the coal (Dai et al.,2007,2008;Renton and Cecil,1979;Reyes-Navarro and Davis,1976;Turner and Richardson,2004).Isolated euhedral pyrite was found only in small amounts insampleFig.4.The variation and cross correlation of ash to the mineral matter,total sulfur,Fe and pyrite contents in the coal samples from Centra Busang and Sebulu coalmines.Fig.5.The variation and cross correlation of ash to the mineral matter,total sulfur,Fe and pyrite contents in the coal samples from Embalut coal mine.156S.Widodo et al./International Journal of Coal Geology 81(2010)151–162TNT-34from Sebulu coal mine (Fig.8c).Clustered euhedral pyrite could not be detected in all analyzed samples.4.2.3.Massive pyriteMassive pyrite is usually found as cleat-/cell-fillings,cementing or coating framboids,euhedral or detrital minerals (Querol et al.,1989).Massive pyrite has also been found as a replacement of organic matter in different macerals (Querol et al.,1989).Many authors denoted pyrite grains with irregular shapes and different sizes by the term massive pyrite (Dai and Chou,2007;Grady,1977;Kortenski and Kostova,1996;Wiese and Fyfe,1986).Renton and Bird (1991)described this type of pyrite as irregular.Massive pyrite was found in most coal samples from Centra Busang and Sebulu.The homogeneous massive pyrite was generally porous and not compact,which is due to the inclusion of relict organic matter and clay minerals during the crystallization processes.Homogeneous massive pyrite was present in lenticular or irregular form.Fig.8d and e show the homogeneous massive pyrite in the coal samples of the Sebulu mine (sample TNT-34).This type of pyrite was not observed in the Embalut coal samples.4.2.4.Anhedral pyriteAnhedral pyrite corresponds to pyrite forms whose shape depends on the shape of the plant debris in which they were deposited.Theanhedral pyrite was divided into two types,the replacement anhedral pyrite and the in filling anhedral pyrite (Kortenski and Kostova,1996;Wiese and Fyfe,1986),which are of late syngenetic and epigenetic origin,respectively.The anhedral pyrite in the sample from Centra Busang and Sebulu coal mines was found in small amounts.Replacement anhedral pyrite was deposited in the lumens of densinite maceral (Fig.8f).The replacement anhedral pyrite was a result of mineralization of cell wall and described to originate from replacement of plant material or massive pyrite replacement of organic matter (Kortenski and Kostova,1996;Querol et al.,1989;Wiese and Fyfe,1986).Anhedral pyrite was not found in the Embalut coal samples.4.2.5.Epigenetic pyrite in cleats and fracturesThe term epigenetic pyrite in cleats and fractures is used for pyrite deposited in fractures or cleats which determine the path of solutions penetrating a coal seam.There are two types of epigenetic pyrite in cleat and fracture:in filling and replacing epigenetic pyrite.The in filling epigenetic pyrite in cleat and fracture has again been divided in two types:fracture and cleat filling (Kortenski and Kostova,1996;Querol et al.,1989;Renton and Cecil,1979).Epigenetic pyrite in cleats and fractures is observed only in a very small quantity in the studied coal samples.In filling epigenetic pyrite in cleats and fractures was observed in the Centra Busang coal samples (e.g.,TNT-30,Fig.8f).TheFig.6.Cross correlation of the concentration ratios of Fe (wt.%)to the pyrite content (vol.%)and total sulfur (wt.%)in the coal samples from Centra Busang and Sebulu coalmines.Fig.7.Cross correlation of the concentration ratios of Fe (wt.%)to the pyrite content (vol.%)and total sulfur (wt.%)in the coal samples from Embalut coal mine.157S.Widodo et al./International Journal of Coal Geology 81(2010)151–162pyrite grains were deposited in the fractures and cleats of the coals and are of epigenetic origin.Replacing epigenetic pyrite from Sebulu coal samples is shown in the Fig.8g.The grains of pyrite replaced (filled)the cell lumens.Replacing epigenetic in fracture pyrite was also found in the Embalut coal samples (Fig.8h).The pyrite from the Embalut coal sample can be characterized as massive fracture filling pyrite with density-fill in the lumens or fractures (Fig.8i).4.3.Interpretation of coal depositional environment and the difference of pyrite in coalsEnrichment of minerals in coal suggests that the peat was deposited under topogenous conditions resulting in increased (richer)nutrient supply (minerals/detrital in flux).In contrast,coals of low mineral content are generated in general from ombrogenous peat bogs with low nutrient supply (minerals).Supply of mineral to the topogenous peat occurs preferentially by surface water and ground water,while in ombrogenous peat bogs the supply takes place through atmospheric deposition.Pyrite is sometimes the dominating inorganic matter present in the coal and the morphology of pyrite can help to reconstruct the environmental condition during and after peatformation (Casagrande et al.,1977,1980;Dai et al.,2008;Demchuk,1992;Taylor et al.,1998;Wiese and Fyfe,1986).The amount and type of pyrite identi fied in the coals from Centra Busang,Sebulu and Embalut differs signi ficantly.In the Centra Busang and Sebulu coals both syngenetic and epigenetic pyrites appear.Syngenetic framboidal pyrite is partly overgrown by epigenetic pyrite.Typically,primary framboidal pyrite occurs in coals and carbonaceous shales overlain by marine strata (Taylor et al.,1998).In case of the Centra Busang and Sebulu coals,the high abundance of mineral might originate from the erosion of Early Tertiary marine sediments of the Central Kalimantan ridge (Fig.9),delivering suf ficient iron and sulphate for pyrite formation under subaquatic conditions (Fig.9).It is assumed that the Centra Busang and Sebulu coals have been evolved from a topogenous peat deposited under wet forest swamp conditions (Fig.9).This interpretation is veri fied by the high proportion of ash,mineral,sulfur,pyrite and iron contents in the Centra Busang and Sebulu coals.In the Embalut coals,pyrite is found only in epigenetic form resulting from post depositional processes.The absence of framboidal pyrite is consistent with the formation of the coal from an ombrogenous peat.This type of peat receives the water through heavy rainfall and the groundwater table lying below the peatformingFig.8.All photos taken under oil immersion.(a)Bacterial framboidal pyrite (Py)from the Sebulu coal mine (TNT-34),(b)overgrowth framboidal pyrite (Py)from the Centra Busang coal mine (TNT-30),(c)euhedral pyrite (Py)from the Sebulu coal mine (TNT-34),(d)massive pyrite (Py)from the Sebulu coal mine (TNT-34),(e)massive pyrite (Py)from Sebulu coal mine (TNT-34),(f)epigenetic pyrite (Py)in cleats/fractures and anhedral pyrite (Py)from the Sebulu coal mine (TNT-30),(g)replacing epigenetic pyrite (Py)in cleats/fractures from the Sebulu coal mine (TNT-30),(h)replacing epigenetic pyrite (Py)in fractures from Embalut coal mine (KTD-38)(i)and replacement massive pyrite (Py)from Embalut coal mine (sample KTD-38).158S.Widodo et al./International Journal of Coal Geology 81(2010)151–162。