Design of a far-infrared spectrometer for atmospheric thermal emission measurements

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Designofafar-infraredspectrometerforatmospheric

thermalemissionmeasurements

DavidG.Johnson

NASALangleyResearchCenter,Hampton,Virginia,USA

ABSTRACT

Globalmeasurementsoffarinfraredemissionfromtheuppertropospherearerequiredtotestmodelsofcloudradiativeforcing,

watervaporcontinuumemission,andcoolingrates.Spectrawithadequateresolutioncanalsobeusedforretrievingatmo-

spherictemperatureandhumidityproﬁles,andyettherearefewspectrallyresolvedmeasurementsofoutgoinglongwaveﬂuxat

wavelengthslongerthan16µm.Ithasbeendifﬁculttomakemeasurementsinthefarinfraredduetotheneedforliquid-helium

cooleddetectorsandlargeopticstoachieveadequatesensitivityandbandwidth.Wereviewdesignconsiderationsforinfrared

Fouriertransformspectrometers,includingthedependenceofsystemperformanceonbasicsystemparameters,anddiscussthe

prospectsforachievingusefulsensitivityfromasatelliteplatformwithalightweightspectrometerusinguncooleddetectors.

Keywords:Fouriertransformspectrometers;infraredspectroscopy;atmosphericremotesensing;atmospherictemperature;

atmospherichumidity;radiativetransfer

1.INTRODUCTION

Fouriertransformspectrometers(FTS)operatinginthefarinfrared(FIR;deﬁnedhereaswavelengthslongerthan16µm)have

generallyusedcooleddetectors,eitherphotoconductorsoperatingat4.2Korbolometersoperatingatevencoldertemperatures.

Thelowtemperaturesarerequiredbothtoachieveusefulsensitivityand,inthecaseofascanningFTS,toprovidetheneces-

saryelectronicbandwidth.Recentimprovementsinthesensitivityandbandwidthofuncooleddetectorshavemotivatedusto

reconsiderthepossibilityofdemonstratingusefulsensitivitywithanFTSoperatingintheFIRwithuncooleddetectors.

InthefollowingsectionswederiveageneralexpressionforthesensitivityofaFouriertransformspectrometerasafunction

ofbasicsystemparameters.Wethenestimatethesensitivitythatcanbeachievedwiththepresentgenerationofuncooled

detectors,andtheimprovementinperformancethatcouldberealizedwithdetectorsoperatingatthethermalnoiselimit.

2.INTERFEROGRAM

WeconsiderﬁrstaconventionalscanningFTS,shownschematicallyinFigure1.Foramonochromaticsourcetheinterferometer

outputisgivenby

IxI005ηkSdcos2πkx(1)

whereI(x)istheoutputpower,xistheopticalpathdifference(OPD)betweenthetwoarmsoftheinterferometer,I0S205ηkSd,SdS1S2,ηk4RkTk,S1andS2arethepowerateachinput,kisthewavenumber(1/wavelength),and

RkandTkarethebeamsplitterreﬂectanceandtransmittance,respectively.

ForabroadbandsourcetheinterferogramisgivenbytheintegralofEquation(1)asshownbelow:

IxI005∞

∞dkηkSdkcos2πkx(2)

I0∞

∞dkS2k05ηkSdk;(3)

whereSdk,thenetinputspectralpowerperunitwavenumberinterval,isgivenbyS1kS2k,andS1kandS2karethe

spectralpowerperunitwavenumberintervalatinputs1and2,respectively.

+TS2RS1

12TS+RSImage of

fixed mirror

2SOPD ( ) = 2xy

I(x)BeamsplitterFixed mirror

Moving mirror

Figure1.GenericFouriertransformspectrometerlayout.

WeestimatethenetinputspectrumbytakingtheFouriertransformofEquation(2)aftersubtractingtheconstanttermI0:

Sdk∞

∞dxexp2πikx∞

∞dk05ηkSdkcos2πkx(4)

05ηkSdk;(5)

whereSkistheestimatednetinputspectrum.

InpracticetheinputsS1andS2(ortheoutputIx)areopticallyﬁlteredtoproduceaband-limitedinterferogram,andwe

furtherreducethenoisebypassingthedetectoroutputthroughanelectronicﬁltermatchedtotheopticalbandpassandmirror

scanvelocity.WethenestimateSdkfromthediscreteFouriertransform(DFT)oftheband-limitedinterferogram1:

Sdkn∆Hn;(6)

HnN21∑

jN2exp2πknxjIjI0(7)

whereHnistheDFTofIjI0,IjIxj,xjj∆,knnN∆,Nisthetotalnumberofsamples,and∆isthedifferencein

opticalpathbetweeninterferogramsamples.Notethatwehaveassumedthattheinterferogramisfullytwo-sided,

WecombineEqs.(5)and(6)tosolveforHnasafunctionofthenetinputpowerperunitwavenumber:

Hn05ηkSdkn∆(8)

Toestimatetheresponseofaparticularinterferometertoaninputofknownnetspectralintensityweneedtoconsider

opticalthroughputandspectralresponseofthedetector.Tosimplifythepresentdiscussionweassumethatthespectrometer

fullyilluminatesadetectorofareaAwithabeamhavingthefocalratiof,andthatthespectralresponseofthedetector,ﬁlters,

andotheroptics(exceptthebeamsplitter)isrepresentedbyasingleefﬁciencyεk.Theeffective(detected)netspectralpower

perunitwavenumber(Sd)isgivenby:

SdkεkFdkπA4f2(9)

whereFdisthenetinputspectralintensity.3.NOISE

Wenowconsidertheeffectofnoiseontheinterferogram.Weassumethatnoiseisgivenbythefunctiongx,andthatthe

observedinterferogramisgivenbyIxgx.Wedeﬁnegjgxj,wherexjisdeﬁnedabove.ThevarianceintheDFTof

gjisrelatedtothevarianceofgjbythediscreteversionofParseval’sTheorem1:

VarGnNVargj(10)

whereGnistheDFTofgj,Varysigniﬁesthevarianceofy,andNisdeﬁnedabove.Thevarianceofgjisrelatedtothespeciﬁc

detectivityandelectronicbandwidthofthedetectorandpreampliﬁerasfollows:

VargjAνBD2(11)

whereνBisthepreampliﬁerbandwidthandDisthespeciﬁcdetectivityofthedetector.AftersubstitutingEquation(11)in

恒温NDIR二氧化碳气体传感器研究

第５１卷　第２期激光与红外Ｖｏｌ．５１，Ｎｏ．２　２０２１年２月ＬＡＳＥＲ　＆　ＩＮＦＲＡＲＥＤＦｅｂｒｕａｒｙ，２０２１

文章编号：１００１５０７８（２０２１）０２０１８９０７·红外技术及应用·

恒温ＮＤＩＲ二氧化碳气体传感器研究

裴　昱１，张加宏１，２，李　敏１，顾　芳１

（１南京信息工程大学电子与信息工程学院，江苏南京２１００４４；２南京信息工程大学江苏省大气环境与装备技术协同创新中心，江苏南京２１００４４）

摘　要：环境温度变化会影响ＣＯ２对红外光的吸收效率，为提高非色散红外（ＮＤＩＲ）ＣＯ２气体

传感器的测量精度，设计了一种基于增量式ＰＩＤ算法的恒温ＣＯ２气体传感器系统。首先利用

ＡＮＳＹＳＦＬＵＥＮＴ软件对恒温控制下的采样气室内部热分布进行模拟仿真，验证了恒温控制的

可行性，然后设计了基于ＰＩ加热片的恒温控制系统。实验结果表明，在０～２０００ｐｐｍ气体浓

度范围内，本文提出的ＣＯ２气体传感器在恒温４０℃时的测量误差小于±６０ｐｐｍ，该结果对于

研制高性能气体传感器有一定参考价值。

关键词：非色散红外；增量式ＰＩＤ算法；ＦＬＵＥＮＴ仿真；恒温ＣＯ２气体传感器

中图分类号：ＴＰ２１９；ＴＮ２１９文献标识码：ＡＤＯＩ：１０．３９６９／ｊ．ｉｓｓｎ．１００１５０７８．２０２１．０２．０１０

ＲｅｓｅａｒｃｈｏｎｃｏｎｓｔａｎｔｔｅｍｐｅｒａｔｕｒｅＮＤＩＲｃａｒｂｏｎｄｉｏｘｉｄｅｇａｓｓｅｎｓｏｒ

ＰＥＩＹｕ１，ＺＨＡＮＧＪｉａｈｏｎｇ１，２，ＬＩＭｉｎ１，ＧＵＦａｎｇ１

（１．ＳｃｈｏｏｌｏｆＥｌｅｃｔｒｏｎｉｃａｎｄＩｎｆｏｒｍａｔｉｏｎＥｎｇｉｎｅｅｒｉｎｇ，ＮａｎｊｉｎｇＵｎｉｖｅｒｓｉｔｙｏｆＩｎｆｏｒｍａｔｉｏｎＳｃｉｅｎｃｅａｎｄＴｅｃｈｎｏｌｏｇｙ，Ｎａｎｊｉｎｇ２１００４４，Ｃｈｉｎａ；２．ＪｉａｎｇｓｕＣｏｌｌａｂｏｒａｔｉｖｅＩｎｎｏｖａｔｉｏｎＣｅｎｔｅｒｏｎＡｔｍｏｓｐｈｅｒｉｃＥｎｖｉｒｏｎｍｅｎｔａｎｄＥｑｕｉｐｍｅｎｔＴｅｃｈｎｏｌｏｇｙ，ＮａｎｊｉｎｇＵｎｉｖｅｒｓｉｔｙｏｆＩｎｆｏｒｍａｔｉｏｎＳｃｉｅｎｃｅａｎｄＴｅｃｈｎｏｌｏｇｙ，Ｎａｎｊｉｎｇ２１００４４，Ｃｈｉｎａ）

辐射特性测量大气传输修正研究_大气辐射传输模式和关键大气参数分析_魏合理

辐射特性测量大气传输修正研究：大气辐射传输模式和关键大气参数分析魏合理1,2，戴聪明1(1.中国科学院安徽光学精密机械研究所中国科学院大气成分与光学重点实验室，安徽合肥2300312.中国科学技术大学环境光学学院，安徽合肥230031)摘要：工作于大气中的光电测量(或遥感)设备接收的目标辐射信号受大气衰减和大气背景辐射影响。大气传输修正是目标辐射特性测量的一个重要环节。介绍了目前国际上实用的大气辐射传输计算模式及影响大气传输的重要大气光学参数的探测方法。对影响红外波段大气传输的重要大气光学参数作了分析，论证了辐射测量大气传输修正系统必须测量的大气参数。关键词：大气传输修正；大气辐射传输模式；大气参数；测量中图分类号：P407.6文献标志码：A文章编号：1007-2276(2014)03-0884-07Researchofatmospherictransfercorrectioninradiancemeasurement:atmosphericradiativetransfermodelandtheanalysisofkeyatmosphericparametersWeiHeli1,2,DaiCongming1(1.KeyLaboratoryofAtmosphericCompositionandOpticalRadiation,AnhuiInstituteofOpticsandFineMechanics,ChineseAcademyofSciences,Hefei230031,China;2.SchoolofEnvironmentalSciencesandOptoelectronicTechrology,UniversityofScienceandTechnologyofChina,Hefei230031,China)Abstract:Thesignalofatargetmeasuredbyelectro-opticsdetectorisattenuatedbytheatmosphereandaffectedbyatmosphericbackgroundradiance.Atmospherictransfercorrectionisimportanttothemeasurementoftarget′sradiationcharacteristic.Thecommonly-usedatmosphericradiativetransfermodelsandthedetectingmethodsofimportantatmosphericopticsparametersaffectingatmosphericradiativetransferwereintroduced.Theatmosphericparametersaffectinginfraredradiativetransferwereanalyzed,theanalyzedresultsindictthosekeyatmosphericopticsparametersmustbemeasuredintheatmospherictransfercorrectionsystem.Keywords:atmospherictransfercorrection;atmosphericradiativetransfermodel;atmosphericparameter;

ASTM E543-06 实施无损检验的机构的标准规程Standard

Designation:E543–06

StandardSpeciﬁcationfor

AgenciesPerformingNondestructiveTesting1

ThisstandardisissuedundertheﬁxeddesignationE543;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginaladoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscriptepsilon(e)indicatesaneditorialchangesincethelastrevisionorreapproval.

ThisspeciﬁcationhasbeenapprovedforusebyagenciesoftheDepartmentofDefense.

1.Scope

1.1Thisspeciﬁcationcoversminimumrequirementsfor

agenciesperformingnondestructivetesting(NDT).

1.2Whenusingthisspeciﬁcationtoassessthecapabilityof,

ortoaccreditNDTagencies,GuideE1359shallbeusedasa

basisforthesurvey.Itcanbesupplementedasnecessarywith

moredetailinordertomeettheauditor’sspeciﬁcneeds.

1.3Thisspeciﬁcationcanbeusedasabasistoevaluate

testingorinspectionagencies,orboth,andisintendedforuse

拉曼与AFM联用 TERS

1/5 PN18–AFM

AFM-microRaman and nanoRamanTM

Introduction

The use of Raman microscopy has become an

important tool for the analysis of materials on the

micron scale. The unique confocal and spatial

resolution of the LabRAM series has enabled optical

far field resolution to be pushed to its limits with

often sub-micron resolution achievable.

The next step to material analysis on a smaller

scale has been the combination of Raman

spectroscopic analysis with near field optics and an

Atomic force microscope (AFM). The hybrid

Raman/AFM combination enables nanometric

topographical information to be coupled to chemical

(spectroscopic) information. The unique designs

developed by HORIBA Jobin Yvon enable in-situ

Raman measurements to be made upon various

different AFM units, and for the exploration of new

and evolving techniques such as nanoRaman

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Design of a far-infrared spectrometer for atmospheric thermal emission measurements

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恒温NDIR二氧化碳气体传感器研究

辐射特性测量大气传输修正研究_大气辐射传输模式和关键大气参数分析_魏合理

ASTM E543-06 实施无损检验的机构的标准规程Standard

拉曼与AFM联用 TERS

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