遙感物理-紅外遙感2009-3

1、第六章第六章熱紅外遙感熱紅外遙感u第一節(jié)第一節(jié)熱紅外遙感概論熱紅外遙感概論u第二節(jié)第二節(jié)海面溫度遙感海面溫度遙感u第三節(jié)第三節(jié)陸面溫度遙感陸面溫度遙感u第四節(jié)第四節(jié)熱紅外多角度遙感信息模型熱紅外多角度遙感信息模型第三節(jié)第三節(jié)陸面溫度遙感陸面溫度遙感6.3.1 陸面溫度遙感反演概述陸面溫度遙感反演概述6.3.2 陸面地表溫度的分裂窗反演算法陸面地表溫度的分裂窗反演算法6.3.3 地表比輻射率的遙感反演方法地表比輻射率的遙感反演方法1. 陸面溫度遙感反演面臨的主要問題陸面溫度遙感反演面臨的主要問題非同溫混合象元占絕大多數(shù)，對(duì)這樣的象元而言，定義象元的非同溫混合象元占絕大多數(shù)，對(duì)這樣的象元而言，定義

2、象元的有效平均溫度也比較困難，關(guān)于這類非同溫混合象元的陸面溫有效平均溫度也比較困難，關(guān)于這類非同溫混合象元的陸面溫度遙感問題需要專門討論。度遙感問題需要專門討論。對(duì)純象元陸面溫度的遙感問題，由于陸面目標(biāo)的比輻射率明顯對(duì)純象元陸面溫度的遙感問題，由于陸面目標(biāo)的比輻射率明顯小于小于“1”1”，所以需要考慮大氣下行輻射的貢獻(xiàn)與干擾。，所以需要考慮大氣下行輻射的貢獻(xiàn)與干擾。(1)(1)陸面目標(biāo)的比輻射率往往受物理狀況（如土壤比輻射率隨土壤陸面目標(biāo)的比輻射率往往受物理狀況（如土壤比輻射率隨土壤含水量而變），表面粗糙度、地表起伏造成傳感器對(duì)地表實(shí)際含水量而變），表面粗糙度、地表起伏造成傳感器對(duì)地表實(shí)際視角

3、的起伏等因子控制，所以一般只能作為未知量，不能事先視角的起伏等因子控制，所以一般只能作為未知量，不能事先設(shè)定。設(shè)定。6.3.1 陸面溫度遙感反演概述陸面溫度遙感反演概述大氣效應(yīng)糾正大氣效應(yīng)糾正 地表真實(shí)輻射亮度值地表真實(shí)輻射亮度值地表真實(shí)比輻射率值地表真實(shí)比輻射率值(4) (4) 陸面目標(biāo)的比輻射隨波段變化顯著，這樣導(dǎo)致方程組陸面目標(biāo)的比輻射隨波段變化顯著，這樣導(dǎo)致方程組的完備，因?yàn)榈谝粋€(gè)波段包含一個(gè)未知的比輻射率，的完備，因?yàn)榈谝粋€(gè)波段包含一個(gè)未知的比輻射率，N N個(gè)波個(gè)波段包含段包含N N個(gè)未知比輻射率，外加一個(gè)未知溫度，所以未知數(shù)個(gè)未知比輻射率，外加一個(gè)未知溫度，所以未知數(shù)總比獨(dú)立方程數(shù)

4、多一個(gè)?？偙泉?dú)立方程數(shù)多一個(gè)。m2. 2. 陸面溫度遙感反演回顧陸面溫度遙感反演回顧陸面溫度的遙感反演問題最早可追溯到陸面溫度的遙感反演問題最早可追溯到TIROS2TIROS2上搭載的熱紅外上搭載的熱紅外輻射計(jì)，其波段為輻射計(jì)，其波段為8-14 8-14 。大家發(fā)現(xiàn)傳感器得到的陸面溫度和地面。大家發(fā)現(xiàn)傳感器得到的陸面溫度和地面實(shí)測的沙漠表面溫度差異很大。實(shí)測的沙漠表面溫度差異很大。Buettner and Kern(1965)Buettner and Kern(1965)通過測量沙通過測量沙子子( (石英含量高石英含量高) )的比輻射率，發(fā)現(xiàn)沙子的比輻射率明顯小于，解釋的比輻射率，發(fā)現(xiàn)沙子的比

5、輻射率明顯小于，解釋了這個(gè)矛盾。了這個(gè)矛盾。Nimbus 4Nimbus 4上的上的IRISIRIS測量結(jié)果也證實(shí)了沙地在測量結(jié)果也證實(shí)了沙地在9 9 附近輻附近輻射率明顯小于射率明顯小于(Prabhara and dalu 1976)(Prabhara and dalu 1976)。 Marlatt(1967)Marlatt(1967)可能是可能是第一次系統(tǒng)地野外測量了地表比輻射率對(duì)熱輻射的影響。第一次系統(tǒng)地野外測量了地表比輻射率對(duì)熱輻射的影響。 m陸面溫度遙感反演的研究到陸面溫度遙感反演的研究到NOAA/AVHRRNOAA/AVHRR第四、五通道在海溫遙第四、五通道在海溫遙感反演取得成功之

6、后，變的越來越有感反演取得成功之后，變的越來越有“誘惑力誘惑力”。Price(1984)Price(1984)首先把首先把海溫遙感的分裂窗口方法引用到農(nóng)田地區(qū)的溫度反演中來。他在仔細(xì)海溫遙感的分裂窗口方法引用到農(nóng)田地區(qū)的溫度反演中來。他在仔細(xì)分析了各種誤差來源之后，預(yù)計(jì)反演精度約分析了各種誤差來源之后，預(yù)計(jì)反演精度約 3K3K。在。在 1 1時(shí)，他給出時(shí)，他給出的反演公式為：的反演公式為： PricePrice指出當(dāng)溫度為指出當(dāng)溫度為300K300K時(shí)，時(shí)， 誤差誤差0.010.01可引起可引起2K2K的溫度誤差。的溫度誤差。sTTTTT .().()445454533335450750ABe

7、cker(1987)Becker(1987)考慮考慮AVHRRAVHRR第四、五通道的地表反射率之差對(duì)溫度第四、五通道的地表反射率之差對(duì)溫度反演的影響，并提出了一個(gè)模型解釋熱紅外測量溫度和地表熱力學(xué)溫反演的影響，并提出了一個(gè)模型解釋熱紅外測量溫度和地表熱力學(xué)溫度的差別。度的差別。Becker(1990a)Becker(1990a)接著在輻射傳輸方程線性近似的基礎(chǔ)上，進(jìn)接著在輻射傳輸方程線性近似的基礎(chǔ)上，進(jìn)一步討論了地表比輻射率對(duì)溫度反演的影響，給出了一個(gè)一步討論了地表比輻射率對(duì)溫度反演的影響，給出了一個(gè)“局地分裂局地分裂窗口窗口”法的反演公式。法的反演公式。 =constant=constan

8、t 是一個(gè)與是一個(gè)與 無關(guān)的獨(dú)立常數(shù)，無關(guān)的獨(dú)立常數(shù)，P P和和M M與與 有關(guān)，可以通過大氣有關(guān)，可以通過大氣輻射傳輸程序輻射傳輸程序Lowtran 7Lowtran 7用最小二乘法回歸確定系數(shù)用最小二乘法回歸確定系數(shù) 。sTATTTTPM04545220AP 112 ()2)1 ( MA0, , , Becker(1990b)Becker(1990b)進(jìn)一步把進(jìn)一步把 NOAA/AVHRRNOAA/AVHRR第三通道的信息考慮進(jìn)來，第三通道的信息考慮進(jìn)來，提出一個(gè)與溫度無關(guān)的獨(dú)立因子。提出一個(gè)與溫度無關(guān)的獨(dú)立因子。Li(1993)Li(1993)在此基礎(chǔ)上討論了用這個(gè)在此基礎(chǔ)上討論了用這個(gè)

9、概念反演地表比輻射率的可行性。他也同時(shí)指出，這種方法要能實(shí)際概念反演地表比輻射率的可行性。他也同時(shí)指出，這種方法要能實(shí)際應(yīng)用還有許多工作要做，其中兩個(gè)最大的制約因素是：應(yīng)用還有許多工作要做，其中兩個(gè)最大的制約因素是：(1)(1)太陽的中紅外輻射受大氣衰減比較嚴(yán)重，如何找到一個(gè)合理太陽的中紅外輻射受大氣衰減比較嚴(yán)重，如何找到一個(gè)合理的方法或模型來估算太陽輻射對(duì)第三通道的中紅外波段的貢獻(xiàn)；的方法或模型來估算太陽輻射對(duì)第三通道的中紅外波段的貢獻(xiàn)；(2)(2)地表在第三通道的中紅外波段的雙向反射率特性比第四、五地表在第三通道的中紅外波段的雙向反射率特性比第四、五通道更強(qiáng)烈，有必要做更多的野外實(shí)測和理論

10、工作以建立地表在第三通道更強(qiáng)烈，有必要做更多的野外實(shí)測和理論工作以建立地表在第三通道的雙向反射率模型。通道的雙向反射率模型。 Gillespie et al.(1986,1987)Gillespie et al.(1986,1987)也討論了把地表比輻射率和地表也討論了把地表比輻射率和地表溫度對(duì)輻射測量的影響分離開的問題。溫度對(duì)輻射測量的影響分離開的問題。Wan Wan 和和 Dozier(1989)Dozier(1989)把遙測地表溫度當(dāng)作一個(gè)地球物理學(xué)的反把遙測地表溫度當(dāng)作一個(gè)地球物理學(xué)的反演問題演問題, ,通過通過LowtranLowtran程序進(jìn)行數(shù)值模擬程序進(jìn)行數(shù)值模擬, ,評(píng)價(jià)了溫

11、度反演的可行性并提評(píng)價(jià)了溫度反演的可行性并提出了合理的波譜段范圍出了合理的波譜段范圍, ,認(rèn)為通過多波譜同時(shí)反演地表溫度和地表比輻認(rèn)為通過多波譜同時(shí)反演地表溫度和地表比輻射率是可行的。射率是可行的。Wan Wan 和和 Dozier(1996)Dozier(1996)通過大氣傳輸模型進(jìn)一步模擬計(jì)算指出：通過大氣傳輸模型進(jìn)一步模擬計(jì)算指出：1)1)統(tǒng)計(jì)回歸的系數(shù)與傳感器的視角有關(guān)；統(tǒng)計(jì)回歸的系數(shù)與傳感器的視角有關(guān)；2)2)為了提高反演精度，模擬為了提高反演精度，模擬計(jì)算回歸系數(shù)時(shí)有必要把大氣含水量、大氣低層溫度和地表溫度考慮計(jì)算回歸系數(shù)時(shí)有必要把大氣含水量、大氣低層溫度和地表溫度考慮進(jìn)去進(jìn)去,

12、,而不能在所有的情況下都用相同的系數(shù)來反演地表溫度。而不能在所有的情況下都用相同的系數(shù)來反演地表溫度。 Prata(1991) Prata(1991)在線性假設(shè)的基礎(chǔ)上，用在線性假設(shè)的基礎(chǔ)上，用NOAA/TOVSNOAA/TOVS反演大氣水汽反演大氣水汽和溫度廓線作大氣修正，建立了一個(gè)地表溫度反演的理論公式。和溫度廓線作大氣修正，建立了一個(gè)地表溫度反演的理論公式。Prata(1993)Prata(1993)進(jìn)一步在理論推導(dǎo)的基礎(chǔ)上給出可地表溫度的雙通進(jìn)一步在理論推導(dǎo)的基礎(chǔ)上給出可地表溫度的雙通道反演公式：道反演公式： 分別為第四、五通道的透過率，分別為第四、五通道的透過率， 為大氣平均溫度，可

13、以近為大氣平均溫度，可以近似用似用 代替，代替， 為大氣下行輻射的改變值，為大氣下行輻射的改變值，PrataPrata給出了不同時(shí)給出了不同時(shí)間和地區(qū)的間和地區(qū)的 值。值。TaTbTds45at111454 bt 545111()dcIBTabTBTBTTT414411 ()( )1145tt45tt45,TTT45或IIVidal(1994)Vidal(1994)把第四、五通道的溫度先轉(zhuǎn)化為把第四、五通道的溫度先轉(zhuǎn)化為8-14 8-14 寬通道的寬通道的黑體亮度溫度，再根據(jù)地表比輻射率改正得到地表溫度，系數(shù)通過回黑體亮度溫度，再根據(jù)地表比輻射率改正得到地表溫度，系數(shù)通過回歸得到，相關(guān)系數(shù)歸得

14、到，相關(guān)系數(shù) =0.89 =0.89 。mR230015020.2958. 345. 554BBsBBTTTTTSobrino(1994)Sobrino(1994)考慮大氣透過率的非線性特點(diǎn)，利用考慮大氣透過率的非線性特點(diǎn)，利用Klesspies Klesspies 和和McMillin(1990)McMillin(1990)提出的估算大氣第四、五通道的透過率之比的方法。提出的估算大氣第四、五通道的透過率之比的方法。把大氣兩各通道透過率之比和地表比輻射率的影響同時(shí)考慮進(jìn)來，改把大氣兩各通道透過率之比和地表比輻射率的影響同時(shí)考慮進(jìn)來，改進(jìn)了地表溫度反演的分裂窗口方法。進(jìn)了地表溫度反演的分裂窗口方

15、法。其中：其中： R R為第四、五通道大氣透過率之比。通過模擬計(jì)算，為第四、五通道大氣透過率之比。通過模擬計(jì)算，SobrinoSobrino指指出，在出，在 已知的條件下，這種方法的精度可以達(dá)到已知的條件下，這種方法的精度可以達(dá)到0.4K0.4K以內(nèi)。以內(nèi)。BTRBTRBTRs41244344556()()()()()()iiii0142451 ()()RTTTTTTkkkNkkN()()()440550144021為了提高分裂窗口法反演地表溫度的精度，近年來的工作越來越為了提高分裂窗口法反演地表溫度的精度，近年來的工作越來越把大氣狀態(tài)作為溫度反演中的信息。而放棄那種建立對(duì)任何大氣模式都把大氣

16、狀態(tài)作為溫度反演中的信息。而放棄那種建立對(duì)任何大氣模式都適用的適用的“全能全能”模型。模型。FrancoisFrancois和和Ottle(1996)Ottle(1996)指出在指出在 已知的條件下，考慮水汽修正已知的條件下，考慮水汽修正可使地表溫度反演的精度達(dá)到可使地表溫度反演的精度達(dá)到0.20.1K0.20.1K。這以。這以Francois(1996)Francois(1996)，Wan Wan (1996)(1996)，Sobrino(1994)Sobrino(1994)所作的工作為代表。所作的工作為代表?？傊懨鏈囟确囱莸难芯慷嘁苑至汛翱诜椒榛A(chǔ)，為了提高總之，陸面溫度反演的研究多

17、以分裂窗口方法為基礎(chǔ)，為了提高溫度的反演精度，不同的作者主要從多個(gè)方面進(jìn)行了研究。但由于陸面溫度的反演精度，不同的作者主要從多個(gè)方面進(jìn)行了研究。但由于陸面溫度反演問題的復(fù)雜性，迄今為止，陸面溫度反演的研究主要仍以可行溫度反演問題的復(fù)雜性，迄今為止，陸面溫度反演的研究主要仍以可行性研究為主，大氣效應(yīng)的糾正、地表比輻射率性研究為主，大氣效應(yīng)的糾正、地表比輻射率 未知和地表溫度的皮膚未知和地表溫度的皮膚效應(yīng)問題仍制約著陸面溫度遙感反演方法在實(shí)際中的應(yīng)用。效應(yīng)問題仍制約著陸面溫度遙感反演方法在實(shí)際中的應(yīng)用。 單通道法單通道法Single infrared channel methodSingle in

18、frared channel method 多通道法多通道法Multi-channel (Split-Window) methodMulti-channel (Split-Window) method 多角度法多角度法Multi-angle methodMulti-angle method 多通道與多角度結(jié)合法多通道與多角度結(jié)合法Multi-channel and multi-angle methodMulti-channel and multi-angle method6.3.1 陸面溫度遙感反演概述陸面溫度遙感反演概述6.3.2 陸面地表溫度的分裂窗反演算法陸面地表溫度的分裂窗反演算法6.

19、3.3 地表比輻射率的遙感反演方法地表比輻射率的遙感反演方法1. Quantity Measured by Radiometry from Space SatelliteAtmosphereOuterofatmosphereSunSurface),(),(),(),(),(iisaiiiRRRI),()cos(),()(),(1 ()(),(),(ssisissbslatisiiiERRTBRiii4765123Spectral Radiance at Satellite Level at viewing angle ),(),(),(),(),(iisaiiiRRRI),()cos(),()

20、(),(1 ()(),(),(ssisissbslatisiiiERRTBRiiiSpectral Radiance at Ground LeveliI,v:thespectralradianceobservedatgroundlevelv:thethermalpathatmosphericradiance,v:thepathradianceresultingfromscatteringofsolarradiation:theradiationemitteddirectlybysurface.:thedownwardatmosphericthermalradiationandsolardiff

21、usionradiationreflectedbysurface.:thedirectsolarradiationreflectedbysurface.v ,Ts:surfacespectralemissivityandsurfacetemperature,v:thedownwardatmosphericthermalradiance,v:thedownwardsolardiffusionradiation,v:thebi-directionalsurfacespectralreflectivity,v:thesolarirradianceatthetopoftheatmosphere.iRa

22、iRsiRiR123atiRsliRbiiE123During the nighttime or for channels in the 8-14 mThe contribution of solar radiation to the spectral radiation at the TOA is negligible, radiative transfer equation can be simplified as ),(),(),(),(iatiiiRRIiatisiiiRTBR),(1 ()(),(),(At Satellite LevelAt Ground LevelDefiniti

23、on of brightness temperature Ti),(),(iiiITBDefinition of brightness temperature Tgi),(),(igiiRTBuImpact and influence of atmosphere on surface radiationuAbsorption and Re-emissionIn TIR, the main absorption gases in the atm. are H2O, CO2 and O3In 10-12m, the main absorption gas in the atm. is H2OuIm

24、pact and influence of atmosphere on surface radiationu is not only a function of W, but also depends on the distribution of H2O in the atmosphere and the profiles of Ta and PressuresuImpact and influence of atmosphere on surface radiationiataiiRTB1)(aT)()()(iiiiiTTTBTBTBTBRRTTTTiatiiiaiiiiSi)(1)(1 A

25、tmospheric equivalent temperature First order of approximation of Planck function From radiative transfer equationAtmospheric effectsEmissivity effectTgi250255260265270275280285290295300305310315320Tgi-Ti-2-10123456789101112TropicalMidlatitude sum m erMidlatitude winterChannel 4uTemperature Correcti

26、on (Deficit) due to Absorption and Emission of AtmosphereatmT)(1aiiiigatmTTTTTiFor dry atmosphere, or for inversion of Ta profile, , is small, otherwise for wet atmosphere, is large. 1iaTTatmTatmTFor a given atmosphere, temperature correction is linearly correlated to Ti or ground brightness tempera

27、ture Tgi atmTTropical atm: W=4.11g/cm2, Ta(0)=299.7KMidlatitude Summer: W=2.99g/cm2, Ta(0)=294.2KMidlatitude Winter: W=0.85g/cm2, Ta(0)=272.2Kand are constant for a reference temperature uImpact of surface emissivityuVariation of surface emissivityuIn 8-13 m， may vary from 0.90 to 0.99uIn 3-5 m，the

28、range of variation may be very large Power expression of the Plancks functioniniiTTB)(iin5 . 411mn137 . 3mn Temperature correction caused by surface emissivityTiigiinTTi11)(iigiatiTBRFor a given temperature, when W increases, increases decreases If no atmosphere, , reaches its maximum, thus, the dri

29、er the atmosphere is, the bigger the impact of surface emissivity on Ts retrieval is iT0iTFor a given atmosphere, the higher Ts is, the smaller is and the bigger is, otherwise the smaller is.iTTBecause is inversely proportional to , thus for a given , the longer the wavelength of channel is, the big

30、ger is.TinTTBRRTTTTiatiiiaiiiiSi)(1)(1i0,890,900,910,920,930,940,950,960,970,980,991,00Ts-Tgi0123456TropicalMidlatitude summerMidlatitude winterChannel 4different slopes correspond to different Ts (20 C variation) for same atmosphereError on Ts retrieval resulted from error on emissivity6 . 02 . 0至T

31、Data pre-processingMeasurement of Land Surface Temperature From SpaceSatellite dataEmissivity RetrievalTemperature RetrievalRadiometric CalibrationImage NavigationGeometric CorrectionsCloud ScreeningAtm. Correction Vis/NIRAtm. Correction TIRNDVI or Classifi.methodsTISI Method (day/night)Split Window

32、Radiative transfer2. Multi-channel (Split-Window) methodThismethodisbasedonthedifferentialabsorptioninthetwoadjacentchannels,centeredat11and12m,tocorrectforatmosphericeffects.cbTaTTjisCoefficientspre-determinedtominimizetheerrorinTsdeterminationBrightnesstemperaturemeasuredintwoadjacentchannelsi and

33、jSurfacetemperatureTheaccuracyofTsretrievalisdependentonthecorrectchoiceofthecoefficientsa, bandcThistypeofmethodhasbeeninitiallydevelopedwithsuccesstodetermineseasurfacetemperature,ithasbeenextendedinthelaterof1980sandinthebeginningof1990storetrievesurfacetemperatureoverlandLand Surface Temperature

34、 Retrieval Local Split Window),(),(),(121211111211WcTWbTWaTsSplit-WindowmethodisextremelysimpleandhasproventobeveryefficientandaccurateforretrievingSSTSplit-WindowcannotbeusedforretrievingLSTwithoutmodificationsLSTcanbeexpressedasalinearcombinationofT11andT12The coefficients a, b and c are generally

35、 function of W in the atmosphere, view angle as well as surface emissivities in these two adjacent channelsThe values of a, b and c are sensor dependent. They depend also on the radiative transfer code and the variation of surface and atmospheric parameters used to derive them For relative drier atm

36、osphere (w2.0g/cm2), a, b and c are local coefficients which depend only on surface emissivities Land Surface Temperature Retrieval Local Split WindowAn algorithm for AVHRR/NOAA14),(),(),(121211111211WcTWbTWaLST2),(2),(),(1211121112111211TTWQTTWPWcLSTor baPbaQModtran4.0;Viewzenithangle0-67;Ts:250-33

37、0K;:0.90-1.00;:-0.020.02Wc)sec41. 004. 0(sec42. 445. 2 121111sec0161. 00479. 0sec0108. 03012. 01sec32 . 90101. 0sec31 . 61918. 0)sec01974. 09907. 0(WWeeP121111sec49. 110. 81sec72. 175. 4)sec48. 011. 0()sec09. 061. 3(WQ834Atmospheres,W5.0g/cm2with3. Determination of Atmospheric Water Vapor Satellite

38、Sounding (TOVS, MODIS, AIRS, IASI) Meteorological Station (Radiosounding) Satellite Measurements Near-infrared techniquesRequirements: at least one channel in the water absorption band (0.94 m), and one nearby channel in the atmospheric windows (0.86 m, 1.05 m and 1.24 m). Passive microwave techniqu

39、es Thermal infrared techniquesRequirements: Two nearby thermal infrared channels one channel near to the water vapor absorption band (12-13 m), and one nearby channel in the atmospheric windows (10-11 m) . .Determination of Atmospheric Water Vapor from Split WindowChannel Measurements Principle of t

40、he MethodiatiiatiisiiiiiRRTBTBI1Ii : radiance measured from space in channel i : brightness temperature in channel i at satellite level, : surface emissivity in channel i, : surface temperature : total atmospheric transmittance in channel i, : atmospheric upwelling and downwelling radiances in chann

41、el i, iTisTatiRatiRiAssumptionsAtmosphere and are unchanged over the N neighboring pixels Or effects of their spatial variations are not larger than the effect of instrument noise over the N neighboring pixels Only surface temperature changes over the N neighboring pixels iRelationship between and P

42、rinciple of MethodsksiiikiTTTT,iTsTk:pixelkoftheNneighboringpixels :mean(orthemedian)TioftheNneighboringpixels :mean(orthemedian)TsoftheNneighboringpixels iTsTFor measurements in channel jsksjjjkjTTTT,0,jkjijijikiTTTTRelationship between and iTjTPrinciple of MethodjijiijRNkikijkjNkikijiTTTTTTR12,1,)

43、()( By least-squares analysis, one gets withijijjiRNkjkjjkjNkikiijTTTTTTR12,1,)()(withvRemarks:Thenumeratoranddenominatoronther.h.s.represent,respectively,thecovarianceandthevarianceofTdirectlymeasuredbythesatellitethetransmittanceratioscanbederiveddirectlyfromsatellitedataprovidedthattheemissivityr

44、atiooftwochannelsareknown Principle of MethodSquare of the linear correlation coefficient of two measurements ijjiNkjkjNkikijkjNkikiRRTTTTTTTTr12,12,2,1,2)()()(12jjiiiijjijjiRRr ThisindicatesthatthetransmittanceratioderivedfromaboveequationsisfeasibleonlyifthebrightnesstemperaturesTi andTjmadeinthet

45、wosplit-windowchannelsiandjoverNpixelsareperfectlycorrelated(r=1)oralmostperfectlycorrelated.ThisconstraintcanbeusedtocheckwhethertheassumptionsmadeinthederivationoftransmittanceratioarefulfilledSample No.02040608010012014016018020022024011/12.92.93.94.95.96.97.98.991.001.011.02Igneous RocksMetamorp

46、hicMeteoriteMineralsSedimentarySoilsVegetation+ SnowWaterRocksSoils+Veg.+WaterEmissivityratiosofchannels11mand12mofATSR2calculatedfromthehemisphericreflectancesmeasuredinlaboratorybySalisburyandDAria1992fordifferenttypesofnaturalsurfaces.11211jiijR formostsurfacesatscaleof1kmx1kmSimulation with Modt

47、ran4 for 1761 atmospheres12/11.2.3.4.5.6.7.8.91.0Water Vapor Content (g/cm2)012345678 = 0 = 64.9 Slope = -13.688, Offset = 13.905, r2 = 0.984Slope = -8.004Offset = 8.201r2 = 0.983NOAA 14Relationship between transmittance ratio and W Simulated channel transmittances: atmospherictransmittance/radiance

48、computercode-MODTRAN4.0NOAA14filterresponsefunctions1761atmosphericprofiles:Wupto7.6g/cm2cos .3.4.5.6.7.8.91.01.1Slope or Offset-20-15-10-505101520SlopeOffsetOffset = 4.062 + 9.891 cos r2=0.9994Slope = -3.876 - 9.858 cos r2=0.9995Angular dependence of regression coefficients For NOAA 141112)cos86. 9

49、88. 3(cos89. 906. 4W2/13. 0cmgwithWvaluesretrievedfromsatellitedataarecomparableinmagnitudewithWobservedbyradiosoundings,g/cm2,g/cm2W measured by radiosonde (g/cm2)0.51.01.52.02.53.03.54.0W derived from ATSR data (g/cm2)0.51.01.52.02.53.03.54.0SGP97BarraxCabauw1:1 lineComparison with Radiosonde Meas

50、urements 04. 0W22. 0W第三節(jié)第三節(jié)陸面溫度遙感陸面溫度遙感6.3.1 陸面溫度遙感反演概述陸面溫度遙感反演概述6.3.2 陸面地表溫度的分裂窗反演算法陸面地表溫度的分裂窗反演算法6.3.3 地表比輻射率的遙感反演方法地表比輻射率的遙感反演方法1. Why Measure Surface Emissivity Surface emissivity isAmeasureoftheinherentefficiencyofthesurfacetoconvertheatenergyintoradiantenergyoutsidethesurface.DependsonthevComp

51、ositionofsurfacevRoughnessofsurfacevOtherphysicalparameters(cf.soilmoisture)vwavelengthKnowledge of permits:DiscriminationandsometimesidentificationofdifferenttypesofsurfacesTogetsurfacetemperatureTs:)6030(sTRemarks:hasveryinterestingspectralproperties,isverycomplementarytoVIS,NIRandMicrowave How to

52、 Get Surface Emissivity 1 1From Field or Laboratory MeasurementsSpectralradiometerRadiometercombinedwithCO2laserBoxNeed some assumptions:TsanddonotchangeduringthemeasurementsSurfaceisLambertianoraspecularreflectingunlessacompletesetofisalsomeasuredbHow to Get Surface Emissivity 2 2From space measure

53、ments(1)onthebasisofthestatisticalrelationshipsbetweenandthespectral informationintheVIS/NIR(cf.NDVI/). =a+b log(NDVI)Coefficientsaandbweredeterminedonlyforthe8-14mbandaandbaresurfacedependentVandeGriendandOwe(1993)Using emissivity databaseNeeds:a)ImagesclassificationfromVIS/NIRandTIRimagesb)Fieldan

54、dLaboratoryemissivitymeasurementsforeachclassareNDVIafteratmosphericcorrectionsforforbaresoilandforinfiniteLAIdependentonstudiedimageEmissivity Determination From SpaceUsing NDVI thresholds methodFor,1110565. 09795. 01120275. 09815. 0Reflectivity in channel 1 of AVHRRFormaxminNDVINDVINDVIvf021. 0968

55、. 011vf015. 0974. 012Fraction of Vegetation2minmaxminNDVINDVINDVINDVIfvminNDVINDVI For,maxNDVINDVI 989. 01211maxmin,NDVINDVIUsing TISI Method from a couple of day/night dataFrom space measurements(2)onthebasisofthestatisticalrelationshipbetweentheminimumandthemaximumoftherelativeemissivitydifference

56、inthemultispectralradiometerHow to Get Surface Emissivity 3 3 (Geillespie et al. 1998)The success of this method depends on the number of channels and their placementNot appropriate for AVHRR sensors with only two channels in IRTHow to Get Surface Emissivity 4 4 From space measurements(3)usingmulti-

57、temporalthermalinfraredmeasurementsNeed some assumptions on emissivityDay=night(Watsonetal.,1990;WanandLi1997)day1=day2(GoitaandRayer1999)DayTISIE=NightTISIE(LiandBecker1993)TISIE=appropriateratioofemissivitiesEmissivity Determination From Space (TISI Method) (1)Definition of TISITheradiancemeasured

58、atgroundlevelisgivenbyiatiSiigiiiRTBTBR)1 ()()(UsingthepowerlawapproximationofthePlancksfunctioninsiingiiiCTTRiiWhereCiisacorrectivetermthattakesintoaccounttheatmosphericreflectedradiance:iatiiRRbCi11)(siatiTBRbiTakingtheproductofNwithpowerak(k=1,.N)gkTNiNiaiainasnagiiiNiiiiiCTT111Choosingtheakssuch

59、that01Niiina11NiiinasTthenEmissivity Determination From Space (TISI Method) (2)Definition of TISI (continuation)LeadingtoNiNiainagiiiiCT11with11NiaiiCCDefiningTISIasNinagiiiTCTISI11DefiningTISIEasNiaiiTISIE1TISIETISI Properties of TISITISIisindependentofsurfacetemperatureTISIisdirectlyrelatedtoemiss

60、ivityratioTISIisdirectlymeasurablefromspaceafteratmosphericcorrectionsTISIcanbetailoredtoweightcertainbandsmoreheavilythanothersNkkkkaTISITISI1with01NiiinaCmaybecomputedbyBi(Tgi)insteadofBi(Ts)whereTgiisthehighestTgamongallchannelsusedforagivenpixel.TISI=TISIEisonlytruewhennosolarreflectionoccursTIS