基于室内光谱测量的玉米单叶偏振与二向性反射关系研究

本研究利用多角度光度计实测了玉米单叶的偏振反射比与二向反射比数据。该光度计能够在不同的观测天顶角、入射天顶角和方位角下测量目标物的偏振反射和二向反射,获得地物目标在2π空间的多角度观测数据。通过分析实测的偏振反射和二向反射数据,得出了玉米单叶的偏振反射与二向反射之间关系密切,最大与最小偏振反射比之和的平均数约等于同等观测条件下玉米叶片的二向反射比。该研究成果为植被遥感监测做出了一种新的尝试,并且对偏振光遥感、多角度遥感的深入研究与应用提供了依据。     

偏振反射信息在植被遥感双向反射研究中的作用

本文基于菲涅尔反射公式,结合现有的偏振反射模型对单叶与植被多角度偏振测量结果与理论结合进行分析;通过研究发现,偏振反射在前向散射方向可以通过菲涅尔反射公式进行解释,但是,在后向散射方向则需要考虑其他物理机理。此外,传感器获取的植被偏振信息既可以作为一种"噪声"来剔除,剔除后在可见光波段将相对误差从原来的30%降低到20%以内,又可以作为额外有效的信息源表征植被的结构特征:通过模型参数的大小判断冠层形态的平整程度。本文可以作为植被偏振探测的系统化方法,并且给出植被固有的偏振反射效应规律,即植被越平展光滑,产生的偏振信息越多;同时也将偏振光遥感在植被监测中的有效性凸显出来,即偏振信息的剥离有助于提升双向反射模型的计算精度。     

水面溢油的多角度偏振与二向性反射定量关系研究

水面溢油是最常见的水体污染源之一,在反射、散射和透射电磁辐射的过程中,将表现与它们自身性质有关的偏振特性。因此,对水面溢油的多角度偏振信息探测成为水体定量遥感的一种新手段。偏振反射是伴随目标的二向性反射而产生的,在探测目标地物的二向性反射的同时,可以通过起偏器获得目标地物偏振态的三维空间分布。本文从多角度偏振遥感机理的角度出发,研究了水面溢油的多角度偏振反射与二向性反射之间存在的定量关系,并从实验上验证了其二向性反射、45°偏振、偏振均值三者在2π空间的相应方位角、天顶角、探测角以及通道上的反射比均相等。     

多角度偏振遥感在水体油污染监测中的优势分析

为了更好地进行水体油污染监测,首先简要介绍了多角度偏振探测技术,然后着重分析了水体油污染目标的偏振特性,同时从目标地物反射光谱的偏振探测机理出发,讨论了它们偏振光谱的空间特征,并总结出3条普适规律.结果显示:偏振光谱信息与强度辐射光谱信息相比,目标地物间反射光谱的微小差异得到了增强,且在大角度入射时,增强效果更为明显....     

植被冠层立体结构与叶片倾角的偏振光效应

植被偏振特性研究对于植被监测与组分定量反演具有极其重要的作用。植被冠层的反射辐射具有偏振特性,这种特性与入射辐射和植被冠层结构相关。本文分析了偏振对光子—叶片—冠层之间细微相互作用及其变化的有效探测能力,并利用研究型扫描式偏振辐射仪RSP(Research Scanning Polarimeter)数据系统对比分析了偏振对不同叶倾角分布的估测。通过上述研究得出以下结论:(1)偏振观测能够对光线在冠层立体结构中的透射反射再出射过程给出精细刻画,若不用偏振手段对这一过程进行甄别并去除,则直接测算的植被散射系数会产生高达140%的误差;(2)利用偏振手段可以为高精度大倾角、多时相遥感观测提供可能,以此可改变目前光学遥感小角度、垂直观测的较严格约束;(3)偏振辐射呈现出随波长的稳定特性(相关系数0.96),使得利用偏振手段可以更好地研究冠层结构;(4)不同叶倾角分布对入射辐射存在不同的偏振反射,为利用多角度偏振信息进行遥感植被精细分类提供了新的途径。本文详细描述冠层结构和植被偏振特性的相互作用,通过对冠层立体结构与叶倾角的研究,刻画了植被定量遥感的方向性信息与高精度实现,为高分辨率遥感定量化的有效信息挖掘提供了新手段。     

土壤湿度的偏振反演模型与实验

采用了一种偏振方法来测量土壤湿度,并改进了一种粗糙表面的偏振反射模型。利用该模型对土壤湿度的偏振特性进行了分析与实验,发现该模型模拟数据与实验数据之间存在很强的相关性,进而可以建立该模型中的某些参数与土壤湿度的定量关系,为定量反演土壤湿度提供新的途径。     

航空遥感数据典型自然下垫面偏振特性分析

对于航空航天大气偏振遥感来说,下垫面偏振辐射噪声影响扣除至关重要。本文基于航空偏振遥感数据,探讨了典型自然下垫面对可见光及短波红外波段偏振敏感性。研究发现,在可见光波段与短波红外(2250 nm)波段,植被下垫面偏振反射率线性拟合斜率都接近1,相关系数大于0.95,表明植被偏振反射率对光谱波段不敏感。比较分析了平静水面和存在耀光水面在670 nm和2250 nm两波段的偏振特性,存在耀光的水面其偏振反射率大约是平静水面的3倍。此外,在实验室测量了红砂土和河沙土的偏振反射率,偏振反射率随波段的改变量很小,其与波段的线性拟合斜率仅为10-5量级,说明两者的偏振反射率对波段很不敏感。因此,利用典型自然下垫面在可见和短波红外波段的偏振反射特性,将能够有效进行地气解耦,提高大气偏振遥感精度。     

不同含水量土壤偏振光谱特征定量分析

水分含量是影响土壤偏振光谱特征的重要参数之一,研究土壤不同水分含量的偏振光谱特征在土壤偏振遥感波段的选择和图像解释上具有重要意义,为应用偏振遥感信息进行土壤调查及理化性质的分析提供依据。本文通过在350-2500 nm波段范围内对不同水分含量的土壤进行偏振光谱测试与分析,研究土壤偏振光谱数据与水分含量之间的关系,建模并检验其精度,对影响土壤偏振光谱特征的各个因素设计科学的正交实验,研究含水量、偏振角度、探测角和方位角等各个因素及其交互作用对土壤偏振光谱特征的影响。结果表明,含水量与偏振角度的交互作用和含水量本身对土壤偏振光谱的影响最大,显著性最强,其次是探测角与含水量的交互作用的影响,而偏振角对土壤偏振光谱有一定的影响,其他因素对土壤光谱偏振反射的影响不大。     

大气中性点区域偏振效应的地—气参量研究

随着中国多颗偏振遥感器搭载发射,偏振遥感成为对地观测领域一个新的增长点以及研究热点。由于大气散射具有较强的偏振效应,大气与地表偏振信号的分离是偏振对地进行有效观测和应用的一个现实问题与难点问题。本文利用晴空中有规律的偏振分布以及大气偏振中性点的性质,对利用大气中性点的偏振效应进行地表—大气偏振信息分离的可行性进行了论证。通过对大气中性点在辐射传输过程性质的计算,得出Babinet大气中性点区域的偏振效应以及基于Babinet中性点区域进行偏振对地观测的基本方法,研究重点阐述了从航空遥感和航天遥感两个层面对如何将大气中性点应用于遥感观测进行了讨论。结果表明:(1)Babinet中性点相比于其他两个中性点,更适合于偏振遥感对地观测中地—气偏振参量分离;(2)航空遥感搭载偏振传感器在Babinet中性点区域进行地表探测可以消除大气偏振,突出地物偏振信息,有效进行地—气偏振参量分离;(3)在太阳同步轨道的卫星遥感影像上能够有效识别偏振中性点区域;研究成果有效分离高分辨率偏振遥感地物反演中的大气偏振耦合效应,实现地表偏振反射信息最大化,对于偏振遥感的大气校正以及定量化水平的提升具有实践意义。     

高信息—背景反差比滤波特性的水、雪、植被偏振遥感探测

在光学遥感中,水的强烈镜面反射性和角度选择性使探测器饱和或反射率过低而难以提取有效信息,雪的强反射性和表面敏感性使传感器难以直接探测,植被指数在不同反射强度下的敏感性对经典植被监测方法的精度和有效性提出挑战。偏振手段可大大提高水、雪和植被的遥感识别能力。本文利用地物遥感偏振光效应的高信息—背景反差比滤波特性,解决光学遥感中水、雪的不可测量问题,以及破除植被强光反射条件下无法精细监测的瓶颈。本文从偏振高信息—背景反差比滤波特性理论出发,通过实验证明偏振手段可有效提升水的信息—背景反差比、剥离70%以上的太阳耀光,为强反射特性下的积雪遥感提供必要方法,并最高降低78%的植被监测误差。本文首次推导证明了偏振探测高信息—背景反差比滤波特性机理,在理论指导和实验深化引导下解决了光学遥感中水、雪因探测器饱和而无法测量的问题,并破除了强反射条件下植被无法精细监测的瓶颈。     

Viewing Angle Effect on the Remote Sensing Monitoring of Wheat and Rice Crops

Abstract

Bidirectional reflectance characteristics of a wheat and a rice canopy were studied using radiometric measurements over the two canopies with an Exotech Radiometer Model 100AX. For both rice and wheat, the measurements exhibited significant variations in reflectance amplitude for varying viewing zenith angles and their values decreased from backward to forward scattering direction. Reflectance obtained its maximum value in the backscatter direction for the viewing angle that corresponds approximately to the solar zenith angle at the time of measurements. Canopy background condition (irrigated or non‐irrigated) was an important determining factor of canopy reflectance particularly in the near‐infrared region of the solar spectrum. Furthermore, bidirectional response characteristics of a vegetation canopy were influenced by the amount of vegetation cover.     

Spectral Reflectance Characteristics of the Soils on Basaltic Terrain of Central Indian Plateau

In-situ spectral reflectance characteristics of soils were studied under field conditions with Multiband Ground Truth Radiometer covering 0.45?C0.52, 0.52?C0.59, 0.62?C0.68, and 0.77?C0.86 ??m spectral bands. Twenty-two surface soil samples were studied in laboratory for their spectral reflectance characteristics using ISCO Model S.R. Spectroradiometer in visible wavelength (450?C725 nm), with 25 nm bandwidth, and in infrared wavelength (750?C1550 nm), with 50 nm bandwidth. The Bidirectional reflectance factor representative of spectral reflectance varied from 3.78 to 11.3???m in band 1, 6.09 to 15.41???m in band 2, 8.05 to 19.41???m in band 3, and 12.18 to 31.2???m in band 4. In-situ spectral reflectance in general increases with the wavelength from visible to infrared bands for all the soils. Black soils have relatively lower reflectance as compared to red soils, which is attributed to the variation in the physicochemical properties of soils. Spectral reflectance, under laboratory conditions, for all the soils increases with wavelength from visible to infrared region except at 950 nm and 1200 nm, where reflectance decreased in all soils, due to weaker water absorption bands and also at 1350 nm, due to strong water absorption at this band. The spectral reflectance of red soils were higher, in-situ as well as under laboratory conditions, as compared to black soils, which is attributed to variation in soil colour, organic matter and clay content of soils. It is observed that the spectral reflectance decrease due to moisture content in soils in all the spectral bands because of darker appearance of soils at moist conditions. Laboratory reflectance measurements serve to define the extent to which intrinsic spectral information is available from soils as a consequence of their composition.     

MISR和MODIS二向性反射数据产品的对比分析

利用4种地表类型共16个地面站点的MISR 9个角度反射率数据产品和MODIS反射率数据产品(MOD09A1), 对比两种传感器获取的地表方向反射观测数据和用BRDF模型参数产品计算的方向反射数据, 分析了这两种BRDF模型参数的外推能力。研究结果表明: (1) MISR和MODIS BRDF模型参数数据产品都具有一定的对观测数据以外方向反射的外推能力, 相比用MISR BRDF模型参数数据外推到相应MODIS观测角度方向反射的结果一致性较强。(2) 采用两种BRDF模型参数推算的方向反射率与观测数据的接近程度有随观测天顶角的增大而减弱的趋势, 在观测天顶角较小时一致性较好。(3) 所用数据处理结果显示, MODIS BRDF模型参数数据产品在近垂直主平面方向反射率推算结果相比近主平面方向的推算结果更接近观测数据。     

Inversion of PROSAIL Model for Retrieval of Plant Biophysical Parameters

The current development of satellite technology particularly in the sensors like POLDER and MISR, has emphasized more on directional reflectance measurements (i.e. spectral reflectance of the target measured from different view zenith and azimuth angles) of the earth surface features mainly the vegetation for retrieval of biophysical parameters at regional scale using radiative transfer models. This approach being physical process based and uses directional reflectance measurement has been found to better and more reliable compared to the conventional statistical approach used till date and takes care of anisotropic nature (i.e. reflectance from the target is different if measured from different view angles) of the target. Keeping this in view a field experiment was conducted in mustard crop to evaluate the radiative transfer model for biophysical parameter retrieval through its inversion with the objectives set as (i) to relate canopy biophysical parameters and geometry to its bidirectional reflectance, (ii) to evaluate a canopy reflectance model to best represent the radiative transfer within the canopy for its inversion and (iii) to retrieve crop biophysical parameters through inversion of the model. Two varieties of the mustard crop (Brassica juncea L) were grown with two nitrogen treatments. The bidirectional reflectance data obtained at 5 nm interval for a range of 400–1100 nm were integrated to IRS LISS–II sensor’s four band values using Newton Cotes Integration technique. Biophysical parameters like leaf area index, leaf chlorophyll content, leaf length, plant height and average leaf inclination angle, biomass etc were estimated synchronizing with the bi-directional reflectance measurements. Radiative transfer model PROSAIL model was validated and its inversion was done to retrieve LAI and ALA. Look Up Table (LUT) of Bidirectional reflectance distribution function (BRDF) was prepared simulating through PROSAIL model varying only LAI (0.2 interval from 1.2 to 5.4 ) and ALA (5° interval from 40° to 55°) parameters and inversion was done using a merit function and numerical optimization technique given by Press et al. (1986). The derived LAI and ALA values from inversion were well matched with observed one with RMSE 0.521 and 5.57, respectively.     

Study of fractional vegetation cover using high spectral resolution data

A field experiment was conducted to study the effect of vegetation cover on soil spectra and relationship of spectral indices with vegetation cover. Multi-date spectral measurements were carried out on twelve wheat fields. Five sets of measurements were taken during the growth period of wheat crop. Field reflectance data were collected in the range 350 to 1800 nm using ASD spectroradiometer. Analysis of data was done to select narrow spectral bands for estimation of ground cover. The ratio of reflectance from vegetation covered soil and reflectance from bare soil indicated that spectral reflectance at 670 and 710 nm are the most sensitive bands. Two bands in visible (670 and 560 nm), three bands in near infrared (710, 870 and 1100 nm) and three bands in middle infrared (1480, 1700 and 1800 nm) were found highly correlated with fractional cover. Vegetation indices developed using narrow band spectral data have been found to be better than those developed using broad- band data for estimation of ground cover.     

Spectral responses of jojoba under salinity stress

Spectral reflectance characteristics of jojoba (Simmondsia chinensis (Link) Schneid.), a dioecious member of Buxaceae have been studied, especially under salinity stress. Reflectance is minimum at bands 1 and 2 (450–520 nm and 520–590 run) of visible range and maximum at bands 3 and 4 (620–680 nm and 770–860 nm) of near infrared range. At all wavelength intervals, male plants have greater reflectance than females. Reflectance in near infrared range (band 4) decreases with increasing age and leaf area index (LAI). A reverse trend occurs at band 3. Absorptance increases in visible as well as Infrared ranges with increasing salinity from control to 10 PSU of sea water concentration.     

天山典型林带积雪的多角度遥感识别

天山中段的山地针叶林带很大程度上影响了该地区整体卫星雪盖的识别精度,多角度卫星遥感技术的发展为林区积雪识别提供了新的途径。本文选取了2000年4月至2001年6月,10个时段研究区内无云覆盖的(Multi-angle Imaging Spectro Radiometer)MISR多角度数据,首先对红光波段不同角度观测结果组成的角度谱图像进行非监督分类,以确定天山林带的分布区域,然后在玛纳斯河中下游与那拉提山东部选取典型像元,分析这些像元红光波段各角度反射率在林区不同积雪覆盖状况下的表现差异。研究发现,若林区存在积雪,0°,±26.1°,±45.6°五个观测角度反射率的平均值大于0.1,在部分降雪月份,后向45.6°观测的反射率大于天顶方向观测的2.5倍。根据这一结论,给出基于MISR数据的研究区不同时段的积雪识别结果。结果表明,MISR红光波段对林区积雪反应敏感,不同角度观测的反射率在林区有雪和无雪时差异较大,故可利用多角度遥感信息进行林区积雪识别。     

Calibration of SCIAMACHY Using AATSR Top-of-Atmosphere Reflectance Over a Hurricane

This letter investigates the synergy between the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) and the Advanced Along Track Scanning Radiometer (AATSR) onboard the ENVISAT platform for reflectance calibration purposes. This calibration study was mainly performed over a portion of a hurricane corresponding to fully cloudy SCIAMACHY and AATSR pixels. Results show that SCIAMACHY underestimates the top-of-atmosphere (TOA) reflectance by up to 23% (at 870 nm) as compared to AATSR for a nadir viewing geometry. Specifically, considering AATSR calibration as accurate, which is confirmed by comparison with the Medium Resolution Imaging Spectrometer, the SCIAMACHY TOA reflectances should be multiplied by 1.21, 1.19, 1.23, and 1.10 for wavelengths at 550, 670, 870, and 1600 nm, respectively, ahead of satellite retrieval schemes based on the measurements of TOA reflectance