下载文档原格式
本技术公开了一种用空间频域成像检测农产品组织光学特性的装置及方法。
包括置于暗箱中的光源系统、成像系统及样品固定调节装置；在暗箱环境下，先后用参比白板和检测对象在不同波长下采集图像，并获得暗场图像，从中选取图像ROI，通过解调处理得到不同空间频率下检测对象的漫反射图像，通过非线性拟合方法处理得到图像ROI每一个像素点的吸收系数和约化散射系数。
本技术能以非接触、单次测量的方式定量获取描述ROI内组织的光学特性变化情况，具有覆盖检测范围广、操作简单、成本低的优势，避免因单次点光源照射而只能获取极小部位光学特性带来的不足，解决了农产品组织光学特性的空间表征问题。
权利要求书1.一种用空间频域成像检测农产品组织光学特性的装置，其特征在于：包括置于暗箱中的光源系统、成像系统及样品固定调节装置，光源系统固定安装在光学平板(17)上，成像系统和样品固定调节装置均通过导轨安装在光学平板(17)上。
2.根据权利要求1所述的一种用空间频域成像检测农产品组织光学特性的装置，其特征在于：所述的光源系统包括播放电脑(18)、DLP投影仪(1)、中性密度滤光片(16)和入射线性偏振片(14)；所述的成像系统包括控制电脑(20)、数字信号产生器(19)、CCD相机(2)、滤波片转轮(3)和接收线性偏振片(5)；所述的样品固定调节装置包括高度可调的样品台(10)、前样品夹(6)和后样品夹(8)；DLP投影仪(1)安装在光学平板(17)上，DLP投影仪(1)镜头的正前方设有样品台(10)，样品台(10)上安装有用于装夹检测对象(7)的前样品夹(6)和后样品夹(8)，DLP投影仪(1)与样品台(10)之间安装有中性密度滤光片(16)和入射线性偏振片(14)，样品台(10)、中性密度滤光片(16)和入射线性偏振片(14)均安装在导轨(11)上并沿导轨移动调整位置；DLP投影仪(1)侧方设有朝向检测对象(7)的CCD相机(2)，CCD相机(2)镜头的正前方依次设有滤波片转轮(3)和接收线性偏振片(5)；播放电脑(18)与DLP投影仪(1)连接；控制电脑(20)与数字信号产生器(19)连接，数字信号产生器(19)与CCD相机(2)连接用以控制CCD相机(2)周期性地采集检测对象(7)反射过来的图像，CCD相机(2)与控制电脑(20)连接用来传输图像采集数据并存储。
第19卷第5期2003年9月农业工程学报T r ansactions of the CSA E V ol.19 N o.5Sept. 2003Advances in measurement and application of physicalproperties of agricultural productsAnnia Garc a Pereira 1,2,Antihu s H ern ndez G mez 1,2,H e Yong1(1.D ep artment of Biosy stems Engineer ing ,Zhej iang University ,H angz hou 310029,China ;2.A g ricultural M echaniz ation Faculty ,H av ana A gr icultural Univiver sity ,Cuba )Abstract :T he phy sical pr opert ies of ag r icultur al pr oducts ar e ver y impor tant in many aspects ,such as to deter mine some phy sical character istics (such as shape,vo lume,size,density ,por o sity ,color and appear ance),fr uit firmness,ripeness lev el and quality ,to ev aluate mechanical damag e in g rains ,seed quality and integr it y ,g enetic cha ng e and ot hers .T he present w or k is a r eview a bo ut some of t he most co mmonly used phy sical pr oper ties o f agr icultural pro ducts such as electr ical conductiv ity ,o ptical pr oper ties,mechanical pr oper ties and ther mal co nductiv ity ,w hich can be used in det ermining o ther pa rameter s and pro per ties such as t he moist ur e co ntent ,density ,micr ow av e dielectr ic frequencies,ripeness lev els,fir mness and ma ny other paramet er s in fr uits,v egetables and gr ains.M any r esear ch result s in t his secto r in the last three decades ar e also highlig hted.Key words :phy sical pr operties;ag ricultural pro duct;m ea sur ement ;mechanical damag e;fr uits and v eget ables CLC number :S12 Document code :A Article ID :1002-6819(2003)05-0007-05Received date:2002-09-28Foundation items:Su pported by the T each ing an d Res earch Award Program for OutstandingYou ng T each ers in Higher EducationInstitutions of M inis try of Education ,C hina ;National Natur al Science Foundation of China (30270773)and Natural Scien ce Foundation of Zh ejiang ProvinceBiograp hy:An nia Garc a Pereira,Ph D candidate,Department.ofBiosystems Engineering ,Zh ejiang Un ivers ity,H angz hou 310029,Chin a;Agricultural Eng ineering Faculty,Havana Agricultural University.National h ighw ay,km 23濎 ,S an J os !de las Lajas,Havana,Cuba. Email:anniagarcia _2000@;Phone 0086-571-86021869,0053-64-63013 Fax:0053-64-63395Corresponding auth or :He Yong,Profess or an d Dean,Department.of Biosystems Engineering ,Zh ejiang Un ivers ity,H angz hou 310029,Chin a.Email:yhe @;Phone 0086-571-86971143;Fax 0086-571-869711431 Introduction T he phy sical pr operties o f agricultural products in the last 40y ears have been investigated by many authors due to its importance in r elation to the deter mination of som e physical characteristics (such as shape ,volum e ,size ,density ,porosity ,color and appear ance ),fruit firmness ,ripeness level and quality ,to evaluate mechanical dam age in g rains ,seed quality and integrity ,g enetical change and others .M any aspects are discussed by the researchers to establish what to measure ,how to m easure it ,and w hat values can be considered generally acceptable by the persons or institutions requir ing such measurement ,available techno logy ,econo mic facto rs and others .T hese proper ties have been investigated by researchers for m ore than 60years ,actually thesehave a w idespread use,and it is hoped that many newtechno logies in relation to fruit and veg etable quality detection w ill appear in this new century beginning.T he main objective of this wo rk is to pr esent an up-to -date information about the most important phy sical properties of agricultural products and their uses,in or der to determine some physical parameters and to protect and ev aluate fruit and vegetable quality.2 Some physical properties of agricultural products and their uses2.1 Electric and dielectric properties It has been dem onstrated in previous scientific w o rk the existing relation among electrical conductivity properties o f ag ricultural pr oducts and m oisture content,due to a regular v ar iation betw een them.Over the years changes in electrical pro perties such as conductivity ,impedance,dielectric constant,dielectric lo ss,or pow er factor have been useful for the measurement of the moisture content in cereals and cereal products,dried fruits,dehydrated vegetables and o ther products.Indeed,m oisture content in m any cases is used to correlate the electrical "conductivity "properties of agricultural products.M oreover electrical conductivity has been used on seeds to predict:germination potential,vigo r,g row th rate,to test cellular m em br ane integr ity ,geneticcharacteristics and mechanical dam age resistance [1～4].T he principle of electrostatic separation has been investigated for separating and cleaning o f ag ricultural seeds depending upon physical char acteristics such as w eig ht,size,shape and sur face tex tur e.T he electrical7co nductiv ity can be influenced by substance co mpo sition and physiological quality of the seeds .Althoug h used o nly for seed quality evaluation the electrical conductivity tests dem onstrate som e characteristics that could be useful in establishing a dam ag e evaluation test fo r g rains .How ever ,tim e co nsum ption is the m ajo r draw back of this m ethod [1].The electrical pr operties may also be used to determine quality among the ions tr ansference,it allow s the establishm ent of some quality levels in fruits,vegetables and seeds. Actually the dielectric properties are w idely used specifically in micro w av e dielectr ic heating pr ocesses.The dielectric proper ties are highly correlated w ith moisture content,because,the dielectric properties of w ater are much gr eater than those of dry matter ,and thus,these pro perties are useful for sensing the moisture co ntent and density through electrical measurement o f these parameters.T he dielectric pr operties deter mine to a large ex tent the behavior o f the material in interacting with high frequency or microw ave field in dielectric heating processes or co oking .Know ledg e of the dielectric properties of the materials to be pr ocessed or m easured is im po rtant in the design of the equipm ent to be used for thesepurposes [5,6].On the other hand dielectric properties of fr uits and v eg etables taking into account their fr equency dependence ,m ay eventually be used to deter mine som e quality factors (as ripeness for example )using non destructive m easur em ents . M icr ow av e dielectric pr operties o f selected fruit and vegetables measured w ith the opened -end coaxial pr obes and netwo rk analyzer ,hav e been repo rted byTr an .[7]from 0.1to 10GHz and by Seaman [8]fr om 0.15to 6.4GHz .Seaman and Seals [8]com pared the perm ittivities of the pulp and skin of pome fruits ("Red Delicio us "and "Golden Delicious "apples ),stone fruit (peaches ),citrus fruits (tangelos and oranges )and bananas ,at room temperature .Significant differences between the dielectric co nstants and loss facto rs for the pulp and skin were found bythem [2].2.2 Optical properties According to optical principles intact agr icultural pr oducts are dense ,light scattering m aterials which requir e a highly sensitive and especially designed spectropho to meter for measuring their spectral transmittance characteristics [9].Optical reflectance has been used to evaluate certain character istics nearthe surface of the pro duct,including m aturity evaluation o f fr uit.Optical pro perties are based o nreflectance ,transmittance ,absor bance ,or scatter of light by the product .When a fruit or v eg etable is exposed to light ,as sho wn in Fig .1,about 4%of the incident light is reflected at the outer surface ,causing specular reflectance or gloss ,and the remaining 96%of incident energ y is transm itted thro ug h the surface into the cellular structure o f the pr oduct w here it is scattered by the sm all interfaces w ithin the tissue or absorbed by cellular constituents [9,10].F ig .1 Incident light on a fr uit or veg etable results in specular r eflectance (g lo ss ),diffuse r eflectance fro m feat ur es at depths to about 5mm (body r eflectance o r inter actance ),diffuse tr ansmittance,or abso rbance.Co lor r esults fr o m v ery shallo w diffuse reflectance Currently multi -w av elength or w hole -spectr aanalytical m ethods are being developed for non -destr uctiv e determ inatio n of so luble so lids ,acids ,starches and ripeness .Starch or so luble solids (SS )content can be determ ined in intact fruit (apple ,citrus ,kiw ifr uit ,mango ,melons ,onion ,peach ,potato and tom ato )[10]. Oil content is impo rtant in seeds,nuts,and avocados and can be deter mined using NIR.Differences betw een sound and damaged tissues in visible and NIR diffuse reflectance are useful for detecting bruises,chilling injur y,scald,decay lesions and num er ous other defects [10].Differences in images taken at specific w av elengths m ultispectral o r hyper spectral imaging and computerized image processing techniques are being used to auto mate detection and classification of many defects on line.In addition to imag ing techno logies,the major adv ances in spectral analysis in recent y ear s have been in statistical methods w hich are being satisfactorily developed for quality assessment.2.3 Thermal propierties Know ledge of ther mal char acteristic such as specific heat,therm al co nductiv ity ,thermal diffusivity,surface conductance and emissivity,as w ell as phy sical characteristics like density ,shape and size are essential for design o f equipment and predicting of the processing of heating o r co oling of ag ricultural8V o l.19,N o.5T r ansactions of the CSA E Sept.2003 pr oducts[11].T he convection heat tr ansfer co efficients are important energ y transpo rt properties in the desig n and operation of food thermal processes,they depend stro ng ly on the apparent viscosity of the fluid foo d or co nsistence of the fruit and the processing equipment. Fr om liter ature rev iew,the str uctural m odel is sugg ested to predict the effective ther mal conductivity of star ch-based solid food fro m the thermal co nductiv ities of the so lid and g as phases,and the po rosity of the material[12].Its dependence w ith the material po rosity permits the use o f thermal properties to determine fruit firmness. Based o n Fikiin et al.and Abbot[10～13]observations, the thermal behavior of fr uit layers in trays may encounter some difficulties.First,the dependence in the heat transfer analysis for every separate fruit using local or product-av erag e surface heat transfer co efficients within pro duct position w ithin layer.This metho d may become ex tremely difficult fr om the beg inning w ith the ex perim ental deter mination of the heat transfer coefficient that needs a large num ber o f measurements to be calculated.Secondly,w hen the w ho le heter ogeneous sy stem of both fruit and outer surro unding air is regarded as a sing le unified system object,w here the system therm al behavior depends o n equivalent(effectiv e)therm ophysical pro perties and surface heat transfer coefficient[14]. T he therm al conductivity between fruit and fruit increases ripeness state over time,also each fruit pr esents therm al conductivity fr om skin to core, independent of shape and size.T hese difference in so me parts of the fruit favors the presence of som e insects,fo r this reason the fruit pro ducers are using different therm al tr eatments alone or in com binatio n w ith cold o r controlled atmosphere(CA)storag e co nditions in order to elim inate these insects.T he fact that the use of thermal treatments can affect fruits qualities,it is very impo rtant to have a complete understanding of the influence of various factor s o n heat transfer in fruits,to minimize adverse effects o n fr uit quality.2.4 Force and mechanical properties T he use o f fo rce and mechanical pro pierties in m ost cases is concentrated in the determinatio n of fruit firm ness.T he im pact force has a close dependence o n impacting v elo city,mass,r adius of cur vature,elastic modulus and characteristics of contact surface.In addition,the ex istence o f high correlatio n betw een impact force w ith fruit m ass and fruit firmness has been ing im pact parameters som e fr uits as apples,pears and av ocados,can be classified into different firm ness groups[15]. Diaz Perez et al.[16]r eported that fruits that feel firm to the hand are found to be soft when checked w ith a penetro meter,these fruits feel as firm as sim ilar fruit assessed ear lier in the cold storag e period. Som e differences betw een penetro meter and non-destr uctiv e measurements are due to the fact that these no n-destructive techniques involv e fruit stiffness measurements and that fruit stiffness does no t necessarily decrease in a mo notonic w ay dur ing sto rage[10]. Using fo rce im pact metho ds the effect of changes in fruit parameter s,can be determ ined,such as(mass, radius of curvatur e,elasticity)and im pact param eters such as(contact speed o r dro p heig ht)on time-domain characteristic of im pact forces;differ ent m ethods for sensing the frecuency components indicative of firmness can be evaluated[17]. U nder mechanical loading,fruits and vegetables exhibit viscoelastic behavior which depends o n bo th, the amount of force applied and the rate of loading. How ever,for practical purposes,they ar e often assumed to be elastic and loading rate is largely ignored.Measurement of elastic pro perties requires consideratio n of only force and defo rmation,w hereas viscoelastic measurement invo lves functions of force, deform ation and tim e[10]. Elastic m odulus can be measured non-destructively, w her eas bioyield and ruptur e by definitio n require some cellular damage.The best relatio nships among senso ry firm ness,hardness and crispness are o btained w ith forces at o r beyond defor matio ns that cause tissue dam age[11].Ther efore a non-destructive m easurement is unlikely to produce ex cellent prediction of these textural attributes or of M agness-T aylor(or similar) test v alues,although useful levels of prediction may be attained in tissues w here elastic mo dulus and rupture strength are closely co rrelated[10].Quasi static tests do not predict im pact pro perties.3 Overview and conclusions 1)The use of force and mechanical pro perties is suitable in the determination of fr uit fir mness.By using im pact parameters some fruits can be classified into different firm ness groups. 2)U nder mechanical lo ading,fr uits and vegetables exhibit viscoelastic behav io r w hich depends on both the amount of force applied and the rate of loading. For practical purposes,elastic and loading may be ignored. 3)Electrical conductivity is suitable to ev aluate9 A nnia G P et al:M easur ing and applying phy sical pr operties of ag ro-pro ductsmechanical damage in grains,and separate small seeds based on density.Electrical conductivity test is also capable of identifying genetical variability,cellular membrane integr ity,and germinativ e potential in different cultiv ars,as well as establishing som e quality levels in fr uits. 4)U sing dielectrical pro perties,moisture contents, density and the behav io r o f som e materials subjected to hig h frecuency like micro wav e fields dielectric heating processes can be determined.5)Thermal proper ties are essential in the desig n o f equipment and in the prediction o f coo ling and heating pr ocesses o f ag ricultur al pr oducts.T hey can be used in determ ining fruit firm ness through the porosity o f the material and it is also very important in po stharvest treatments in o rder to eliminate insects that may reside in some comm odities. 6)Optical properties have been used to evaluate so me characteristics near the surface of the pro duct, including maturity evaluation of fruit,color, appear ance,etc. 7)Through sophisticated m ethods such as multi w avelength o r w hole-spectra analy tical m ethods, w hich are based on optical properties,soluble solids and o il contents,acids,starches and r ipeness,in many fruits and vegetables,varieties can be deter mined. 8)Optical systems,especially in the NIR region, and new er so ftw are has made it possible to detect so me factors that may improve quality index es.[Ref erences][1] Co ut o S M,Silva M A,Reg azzi A J.A n electrica lco nduct ivity metho d suitable for quant itative mechanica l damag e eva luation[J].T ra nsactio ns of t he ASA E,1998,41(2):421～426.[2] I kediala J N,T ang J,Drake S R,et al.D ielectr icpr operties of apple cultivar s and co dling mot h larv ae[J].T ransactio ns o f the A SAE,2000,43(5):1175～1184. [3] N elso n S O,Stetson L E.Ger mination response of sw eetclov er seed to39M Hz electr ical tr eatments[J].T ransactio ns o f the A SAE,1982,25(5):1412～1416. [4] P anobianco M,Vieir a R D,K rzyzanow ski F C,et al.Electrical conductiv ity o f so ybean seed and co rr elat ionwith seed co at lignin co nt ent[J].T r ansactions of t he ASA E,1999,42(1):945～948.[5] Nelson S O.Dielectr ic pr o per ties o f so me fr esh fr uits andveg etables at frequencies of 2.45to22G Hz[J].T r ansactions of the A SA E,1983,26(2):613～616.[6] Nelson S O.M icr ow av e dielectric pr opert ies of fr eshonio ns[J].T r ansact ions of the A SA E,1992,35(3):963～968.[7] T r an V,Stuchly S S,Kr aszew ki A.Dielectr ic pro pertiesof selected veg et ables and fruit s at0.1～10.0GHz[J].J M icr ow ave P ow er,1984,19(4):251～258.[8] Sea man R,Seals J.F ruit pulp and skin dielectricpr opert ies fo r150M Hz to6400M Hz[J].J M icr ow ave Pow er&Elect ro mag Ener gy,1991,26(2):72～81.[9] Belie D N,T u K,Jancsok P,et al.Pr eliminar y study o nthe influence o f turg or pressur e on body r eflectance of r ed laser light as a ripeness indicator fo r apples[J].Posthar vest Bio lo gy and T echnolo gy,1999,16:279～284.[10] A bbo tt J A.Q uality measur ement o f fr uits andveg etables[J].P ostharv est Bio lo gy and T echno lo gy,1999,15:207～225.[11] M o hsenin N.P hysical pr opert ies of plant and animals[A].Structure,phy sica l character istics and mechanicalpro per ties.Go rdon and Br each Science Publisher s,t hePennsylvania St ate U niv ersit y,1970,1:5～20.[12] Sar avacos G D,Ko star opoulos A E.Engineer ingpro per ties in foo d simulation[J].Computers ChamEngng,1996,20.s461～s466.[13] F ikiin A G,F ikiin K A,T ripho no v S D.Equiv alentther mophysical pro per ties and sur face heat t ransfercoefficient of fr uit layer s in tray s dur ing co oling[J].Jour nal of F oo d Eng ineering,1999,40:7～13.[14] Beukema K J,Bruin S.Heat and mass tr ansfer dur ingcoo ling and stor age of ag ricultural pro duct[J].ChemicalEngineer ing Science,1982,37(2):291～298.[15] Ruiz-A ltisent,Jar!n M C,Co rr ea P.Fuit qualitysensing:posthar vest r ipeness[C].Paper N o.935-25.4th Int.Sy mp.On Fr uit,N ut,and V eg etable P ro ductio nEngineer ing.V alencia-Zar ago za,Spain.1993,22～26M ar ch.[16] Diaz-Per ez J C,Bautista S.Q uality chang es in sapotemamey fruit dur ing r ipening and stor ag e[J].Posthar vestBiolog y a nd T echnolog y,2000,18:67～73.[17] Delw iche M,T ang J S,R umsey J W.Co lo r a nd o pt icalpro per ties of cling stone peaches relate to mat ur ity[J].T r ansact ions of the ASA E,1987,30(6):1873～1879.10V o l.19,N o.5T r ansactions of the CSA E Sept.2003 农产品物理特性的检测与应用研究进展A nnia Garc a Pereira1,2,A ntihus Hern ndez G mez1,2,何 勇1(1.浙江大学生物系统工程系,杭州310029; 2.哈瓦那农业大学农业机械系,古巴)摘 要:农产品物理特性在测定农产品的物理特征(如:形状、体积、尺寸、密度、颜色、外观)、水果的坚实度、成熟度和品质及估算谷物的损坏程度、种子的品质、完整性和遗传变化等方面起着非常重要的作用。
DOI:10.16605/ki.1007-7847.2023.05.0154茶陵野生稻冷响应基因OrCrGHl 的表达与克隆收稿日期:2023-05-12;修回日期:2023-06-12;网络首发日期:2023-07-27基金项目:湖南省自然科学基金项目(2023JJ30397,2021JJ50134);长沙市自然科学基金资助项目(kq2202243,kq2014077);湖南师范大学博士科研启动项目(2020);湖南省教育厅重点科研项目(19A289);中国科学院亚热带农业生态过程重点实验室开放基金项目(ISA2015201);湖南省重点科技计划项目(2012FJ2013)作者简介:莫香(1979—),女,湖南岳阳人,博士,实验师,主要从事作物逆境生理与分子生物学研究;*通信作者:徐孟亮(1964—),男,湖南益阳人,博士,湖南师范大学教授,主要从事作物逆境生理学研究及植物生理学教学,E-mail:*****************。
莫香,盛丽丽,罗佳,徐甜甜,徐孟亮*(湖南师范大学生命科学学院作物不育资源创新与利用湖南省重点实验室,中国湖南长沙410081)摘要:为了发现新的水稻耐逆基因,采用水稻基因芯片分析了茶陵野生稻及籼型栽培稻培矮64S 苗期全基因组在冷胁迫下的表达水平,从茶陵野生稻中筛选出一个强烈响应低温的耐冷候选基因,暂命名为OrCrGHl (Oryza rufipogon cold responsive glucan hydrolase-like )。
用实时定量PCR 方法对其表达水平进行了进一步的分析,所得结果与基因芯片分析结果基本吻合。
以茶陵野生稻为材料,用逆转录PCR (reverse transcription PCR,RT-PCR)方法获得了包含其完整开放阅读框(open reading frame,ORF)的cDNA 克隆。
根据其ORF 序列进行预测,该基因编码一个包含558个氨基酸残基的糖基水解酶相似蛋白质,其理论分子质量为59.252kD,pI 为5.81。
肉品新鲜度检测方法
侯瑞锋;黄岚;王忠义;徐志龙
【期刊名称】《现代科学仪器》
【年(卷),期】2005(000)005
【摘要】简单介绍了当前肉品新鲜度检测领域的一些主要测量标准及检测方法,概述了国内外在肉品新鲜度检测领域的研究现状.最后分析了当前在肉品新鲜度检测领域所面临的首要问题.
【总页数】5页(P76-80)
【作者】侯瑞锋;黄岚;王忠义;徐志龙
【作者单位】中国农业大学信息与电气工程学院,北京,100083;中国农业大学信息与电气工程学院,北京,100083;中国农业大学信息与电气工程学院,北京,100083;中国农业大学信息与电气工程学院,北京,100083
【正文语种】中文
【中图分类】S1
【相关文献】
1.中药负离子制剂对猪肉品质和贮藏期新鲜度的影响 [J], 乔鹏飞;王传龙;王震;韩东魁;张敏
2.肉品新鲜度的检测方法 [J], 蒋丽施
3.近红外光谱技术评价肉品新鲜度的应用 [J], 杨莹;庄晓萌;张欣欣;曲高阳;霍思宇;张岚;;;;;;;
4.肉品新鲜度检测方法 [J], 赵月兰;庄玉亭
5.肉品新鲜度检验的研究Ⅱ.改良微量扩散法测定肉品挥发性盐基氮试验 [J], 陈衍基;谭超
因版权原因，仅展示原文概要，查看原文内容请购买。
农产品生物组织的光学参数测量方法研究徐志龙,王忠义,黄 岚,侯瑞锋(中国农业大学信息与电气工程学院北京100083)提要:为解决当前近红外光谱分析技术应用于农产品品质分析时所出现的预测模型不稳定、适应性不好、预测精度难于进一步提高等问题,我们认为,研究组织内部的光学性质及其光传输规律是其关键。
为此,我们首先要对农产品生物组织的光学参数进行检测研究。
本文通过对生物组织光学参数目前常用的一些测量方法进行了分析研究,其中着重介绍了基于空间分辨技术、时间分辨技术和积分球技术的光学参数测量方法,并对这些方法的优缺点做了比较,为选择一种适用于农产品生物组织光学参数的测量方法提供了依据。
关键词:光学参数;Monte Carl o 仿真;空间分辨技术;时间分辨技术;积分球技术中图分类号:S1 文献标识码:A 文章编号:0253-2743(2005)06-0087-03Investigation of measurement methods for determining the optical properties of agricultural products tissueXU Zhi -long ,WANG Zhong -yi ,HU ANG Lan ,HOU R ui -feng(College of Information and Electrical Engineering ,China Agricult ural U niversit y ,Beij ing ,100083,China )Abs tract :At present ,near infrared s pectroscopy technology is widel y applied to quantitative analysis of agricultural products ,but a lot of problems are in the way ,for instance ,the calculation model is not stable and suitable enough for predicted samples ,the prediction precisi on is difficult to be improved more .To re -solve these problems ,we have to study the optical properties and light propagation in tis sue ,and the optical properties measurement methods are studied firstly .In this paper ,a few optical properties meas urement met hods us ed today are presented and investigated ;es peciall y ,the measurement methods bas ed on spatiall y -resolved s pectroscopy ,ti me -resolved s pectroscopy ,and integrating -sphere system are descri bed in detail .Acc ordingl y ,the advantages and dis advantages of these meas urement methods are compared t o s elect a s uitable meas urement method to determine the optical properties of agricultural products tissue .K ey words :optical propert y ;Monte Carlo simulation ;s patiall y -res ol ved technology ;time -resolved technology ;integrating -sphere technol ogy收稿日期:2005-04-05基金项目:科技部“十五”攻关项目(02EFN216900720)资助;中国农业大学信息与电气工程学院创新基金(KY -06)资助通讯作者:王忠义,工学博士,副教授。
作者简介:徐志龙,中国农业大学硕士研究生,研究方向为生物光子学。
1 引言近红外光谱分析技术在农产品品质分析领域的应用已经十分广泛,考虑到农产品形态的多样性和结构的复杂性给定量分析带来的不便,目前它所采用的分析方法多为系统方法,即通过扫描大量样品光谱来建立样品浓度和吸光度之间的相关模型,进而预测未知样品的浓度信息〔1,2〕。
这种分析方法通过对研究对象的封装有效地避开了组织内部原本十分复杂的光传输过程,简化了分析模型:然而,同时也使得光传输过程中吸收和散射变化的细节信息被丢失,结果导致了光和组织的相互作用机理无法解释,光从组织中携带的信息量变化情况不明确,物理意义不清楚等一系列问题,而这些问题恰恰是当前分析模型不稳定、适应性不好、分析精度难于进一步提高等问题的根源所在。
为此,我们有必要从组织内部出发,通过对组织光学特性及其光和组织相互作用规律等问题的研究来挖掘原本被丢失的重要信息,从而为进一步提高分析精确性和稳定性寻找出新的有效途径。
当前,对于生物组织内部光传输规律的研究在生物医学光子学领域已经十分普遍,并且在医学光学诊断、光学治疗上有了一些成功的应用〔3-4〕。
我们通过借鉴它们的研究方法应用到农产品品质分析领域对进一步提高农产品品质分析水平应该是一个契机。
生物医学光子学的研究告诉我们,生物组织光学参数的检测研究对于组织中光传输规律的研究有着重要的基础意义,光在组织内部的光传输、光分布情况归根结底都依赖于组织的光学参数变化。
另外,光学参数作为生物组织内部光学特性的反映,与组织内部生理、病理和代谢过程中的物质变化情况都有着密切联系,这也是生物组织光学参数检测研究的意义所在。
Cheong 等人〔5〕在1990年总结了一份测量生物组织光学参数的清单,其中列举了大量的生物组织光学参数测量结果及其相应的测量方法,为后续的研究工作提供了丰富的参考;然而,这些研究的对象大多集中在人体组织或者动物组织,对于农产品生物组织来说目前还未见相应的报道。
所以,我们对农产品生物组织光学参数的检测研究就显得十分重要。
本文的目的就是希望通过对生物组织光学参数目前一些常用的测量方法进行分析研究,从而为选择一种适用于农产品生物组织的光学参数测量方法提供依据。
2 生物组织光学参数及其测量方法用来描述生物组织光学特性的基本光学参数有三个:吸收系数μa 、散射系数μs 和各向异性散射因子g 。
吸收系数μa 和散射系数μs描述的是光在单位距离内因为被组织吸收或散射而损失的光能变化,单位都是mm -1。
吸收系数μa 反映了生物组织中分子的原子能级信息,散射系数μs 反映了组织结构的显微不均匀性。
各向散射异性因子g 是平均散射余弦,无量纲,用来表征组织中光分布的不均匀性和前向散射的大小,g =1表示完全前向散射,g =0表示完全同向散射,g =-1则表示完全后向散射。
除了上述三个基本光学参数以外,为了研究的方便还定义了其他一些光学参数,如反照率α、穿透深度τ、扩散系数D 等,对于这些光学参数来说,一般都可以由上述三个基本光学参数组合得到,在此就不再赘述。
根据生物组织所处的状态,确定其光学参数的方法一般有两类:一类是离体测量,也称为切片测量法,即根据光学参数的定义将组织切片后置于光学系统中进行测量的方法;一类是活体测量,也称为无损测量法,即通过测量组织表面的漫射光分布再根据特定的光传输理论来反演光学参数的方法。
对于离体生物组织和活体生物组织来说,因为它们所处的生理状态差异较大,所以它们的光学参数也会有所不同。
若观察组织表面的漫射光分布,可以发现,光进入组织后其组织表面的漫射率是随着观察点与入射光源的距离增加而减小的。
根据漫射近似理论,若选择入射光源为连续变化、窄脉冲变化和正弦调制时可以发展出基于空间分辨技术〔6-8〕、时间分辨技术〔9〕和频率分辨技术〔10〕的光学参数测量方法。
目前常用的一般是前两种方法,而基于频率分辨技术的光学参数测量方法是通过对入射光进行调制引起光穿过组织后的相位变化、幅度变化来确定光学参数的一种方法。
2.1 基于连续光源的空间分辨技术当连续光源准直入射到半无限介质表面时,可以认为组织体内的光分布是和时间无关的一种稳态分布,组织表面某观察点距入射光源ρ处的漫反射率也是一定的,如图1所示。
Farrell 等人〔6〕基于稳态漫射方程的推导,采用外延边界条件和两点正负镜像光源的近似方法,得到了组织表面距离光源ρ处的漫反射率公式:R (ρ)=α′4π〔1μ′t (μeff +1r 1)exp (-μeff r 1)r 21+(1μ′t +4A 3μ′t )(μeff +1r 2)exp (-μeff r 2r 22〕图1 组织表面距入射光源ρ处的漫反射率R (ρ)其中,传输反照率α′=μ′s /(μ′s +μa ),μ′s =μs (1-g )是传输散射系数;有效衰减系数μeff =〔3μa (μa +μ′s )〕1/2;总衰减系数μ′t =μa +μ′s ;r 1和r 2是观察点到组织表面附近的正负镜像同性散射点光源之间的几何距离,r 1=〔(1/μ′t )2+ρ2〕1/2,r 2=〔(1/μ′t +4A /3μ′t )2+ρ2〕1/2;A 是组织内部反射系数,若组织和周围介质边界匹配则取A =1,典型的,若组织的相对折射率n =1.4,那么根据Groenhuis 等人〔11〕的计算取A =3.23。
根据上述Farrell 公式,若在适当的组织表面范围内通过光纤或CCD 检测器获取这种漫射光分布的变化情况,那么就可以通过非线性拟合算法推算出组织的光学参数了。
87 《激光杂志》2005年第26卷第6期 LASER J OURNAL (Vol .26.No .6.2005)这里若我们取ρ>5mm ,则对于一般生物组织的光学参数来说应该能够满足ρ>>1/μ′t +4A /3μ′t ,此时就有r 1=r 2=ρ,所以,组织表面距离光源ρ处的漫反射率变为:R (ρ)=α′2π3+2A 3μ′t (μeff +1ρ)exp (-μeff ρ)ρ2 通过这个式子,我们可以简化Farrell 公式的复杂性,在应用中将更具有实际意义。
