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。     

Polarization of reflected light as a function in remote sensing of sea state

Polarizaton characteristics of completely diffuse light reflected from a wind roughened sea surface and its total reflectance are studied for various wind speeds on the assumption that distribution of wave slopes around their mean is Gaussian. The angular distribution of diffuse reflectance and polarization status of reflected light are also estimated with a view to exploring possibilities of using these parameters for remote sensing of sea state from a satellite, aircraft or an observation tower. The efficiency of Brewster’s angle technique in eliminating reflected light from the sea surface radiance for remote sensing of subsurface material is examined for non flat sea surface in the light of these results. the results show that the diffuse light reflected from the sea surface contains information on the sea state in the form of its status of polarization and can be used as an observational tool in remote sensing of sea state. The scope and limitations of the method proposed are discussed.     

REMOTE SENSING METHODS IN THE STUDY OF SOILS IN BELARUS'

Applications of remote sensing in the study of soils of Belarus' are investigated. The focus is upon ascertaining relationships between phototone of cultivated soils and various soil characteristics (humus content, texture, etc.); upon ensuring the best times for imaging; on the revision of existing soil maps from remote sensing imagery; and on determinations of humus content from spectral reflectance values. Translated by Edward Torrey, Alexandria, VA 22308 from: G. V. Dobrovol'skiy and V. L. Andronikov, eds., Aerokosmicheskiye metody v pochvovedenii i ikh ispol'zovaniye v sel'skom khozyaystve: sbornik nauchnykh trudov [Remote Sensing Methods in Soil Science and Their Utilization in Agriculture: A Collection of Scientific Works]. Moscow: Nauka, 1990, pp. 109–116.     

Delineation of coalfield surface fires by thresholding Landsat TM-7 day-time image data

Surface fires are common in coalfields where coal is mined or exposed to sunlight for long durations of time. The heat energy emitted from these fires affects the signal recorded by sensors operating in the shortwave infrared regions of the electromagnetic spectrum. The Landsat TM/ETM+ band-7 is sensitive to solar reflected radiation as well as emitted radiation from a target. The ‘maximum solar reflection threshold’ method proposed in this study uses the highest spectral radiance that can be attributed to solar reflection as the conservative threshold to segregate the pixels with emitted component from those with reflected component of the EM energy. Investigations with Landsat TM/ETM+ data indicate a reflectance value of 0.23–0.25 as the most representative highest reflectance (threshold) in coal mining areas. The method apparently has the advantage that it is based on the reflectance characteristics of materials (sandstone-shale mixtures) typically found in coal mining areas.     

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。     

空间波与长试样法测量介电常数的结果与对照

用空间波法测量无限大半空间模拟介质板的复介电常数 ,包括金属板定标法与双极化法 ,测量中同时接收前向散射的振幅和相位 ,实验在X波段进行。该文的金属板定标法本质上是自由空间中的长试样法 ,并对它的原理和测试结果与波导长试样法作了比较与对照     

双极性天线在多路径效应探测中的应用

多路径效应是影响卫星定位精度和稳定性的重要因素。针对多路径环境复杂多变难以进行分析的问题,该文提出了一种利用双极性天线探测多路径的方法。详细介绍了反射信号的极性特征;通过判断信号的极性可以有效地区分直射信号和反射信号。分析了通过信号极性实现多路径探测的理论:组成双极性天线的右螺旋圆极化天线和左螺旋圆极化天线能够分别输出卫星信号中的右螺旋圆极化分量和左螺旋圆极化分量,如果两个分量的载噪比差值大于一定的门槛值,就可以推断卫星信号在传输过程中经历了多路径效应。最后通过仿真实验验证了该方法的可行性和有效性。     

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。     

扩展多波长偏振测量的太阳—天空辐射计观测网

太阳辐射和大气气溶胶的地基遥感观测在气候变化、大气环境和对地观测等领域有重要意义。结合多波长偏振测量技术在气溶胶观测中的应用,本文介绍了在中国典型区域建立的太阳—天空辐射计观测网SONET(Sunsky radiometer Oberservation NETwork)。主要内容包括:(1)多波长偏振太阳—天空辐射计的参数、基本原理和功能,以及据此建立的中国区域太阳—天空辐射计观测网及其站点的基本情况;(2)太阳直射、太阳主平面和平纬圈几何条件下,太阳—天空辐射和偏振的观测模式及其测量参数;(3)针对气溶胶、水汽等大气成分观测发展的太阳直射辐射、天空光辐亮度、线偏振度等观测量的定标和数据处理方法,并给出在晴朗和灰霾等天气下的SONET观测结果示例;(4)基于在SONET典型站点连续的较长期遥感观测,初步建立了城市、乡村和灰霾情况下的整层大气气溶胶参数模型。在扩展多波长偏振测量的基础上,SONET还发展了自动观测、快速数据处理、定期标定和维护等观测网运行关键技术,可为典型大气气溶胶模型构建、卫星气溶胶产品反演和验证、大气环境遥感监测等应用提供支撑。     

浅析偏振光遥感的应用

偏振光遥感是近年来备受关注的一种新兴对地观测方法.早期的传感器多以目标的反射辐射或自身的辐射强度来推断目标的状态和性质,而把传感器接收信号中的偏振作为一种"噪音"来处理,随着空间遥感科学的发展,科学家们发现偏掁特性是一种良好的地表监测手段.     

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.     

Crop polarisation behavior derived from Multi-Temporal adeos-polder data

This paper reports a study on multi-temporal polarized response of wheat crop from spaceborne ADEOS-POLDER sensor over a homogeneous wheat region of Punjab, India. Both the polarized as well as total reflectance of wheat were observed at different scattering angles for two spectral bands i.e. 670 nm and 865 nm during crop growth from November to April in rabi 1996-97 season. Results show that sun-target-viewing geometry plays an important role in polarization property. The top of atmosphere (TOA) polarized reflectance is found to decrease exponentially with increasing scattering angle. Polarized reflectance of crop was found to be an order of magnitude smaller in comparison to the total reflectance. An attempt was also made to model the observed polarized behavior over an agricultural area using a theoretical simplified crop reflectance model and accounting for atmospheric molecular (Rayleigh) contribution in the single scattering approximation. It was found that there was a decrease in the polarized reflectance at the grain filling (heading) stage of wheat crop. This is in accordance with ground- based observations and can be due to the reduction in the specular component of the reflected light during post-heading stage of the crop.     

Hyperspectral reflectance of leaves and flowers of an outbreak species discriminates season and successional stage of vegetation

Spectral reflectance can be used to assess large-scale performances of plants in the field based on plant nutrient balance as well as composition of defence compounds. However, plant chemical composition is known to vary with season – due to its phenology – and it may even depend on the succession stage of its habitat. Here we investigate (i) how spectral reflectance could be used to discriminate successional and phenological stages of Jacobaea vulgaris in both leaf and flower organs and (ii) if chemical content estimation by reflectance is flower or leaf dependent.We used J. vulgaris, which is a natural outbreak plant species on abandoned arable fields in north-western Europe and studied this species in a chronosequence representing successional development during time since abandonment. The chemical content and reflectance between 400 and 2500 nm wavelengths of flowers and leaves were measured throughout the season in fields of different successional ages. The data were analyzed with multivariate statistics for temporal discrimination and estimation of chemical contents in both leaf and flower organs.Two main effects were revealed by spectral reflectance measurements: (i) both flower and leaf spectra show successional and seasonal changes, but the pattern is complex and organ specific (ii) flower head pyrrolizidine alkaloids, which are involved in plant defence against herbivores, can be detected through hyperspectral reflectance.We conclude that spectral reflectance of both leaves and flowers can provide information on plant performance during season and successional stages. As a result, remote sensing studies of plant performance in complex field situations will benefit from considering hyperspectral reflectance of different plant organs. This approach may enable more detailed studies on the link between spectral information and plant defence dynamics both aboveground and belowground.     

COLOR SYNTHESIS OF MULTISPECTRAL IMAGERY FOR MAPPING PURPOSES

The authors describe common Soviet practice in the making of false-color composite imagery for visual interpretation. Also addressed are standard image interpretation techniques: figure-ground color contrast, color separation (number of color gradations occurring within an average contrast range), and so-called landscape indicator techniques. Related issues, such as selection of spectral bands and filters for specific interpretation tasks, and the changing reflectance characteristics of band-specific intermediate images, receive attention as well. Tables and figures illustrating relationships between photographic contrast, film contrast ratings, optical densities, and spectral bands are included. Translated from: Geodeziya i kartografiya, 1985, No. 4, pp. 41-46.     

NARROW-BAND REMOTE SENSING FROM THE “SALYUT-7” SPACE STATION

An experiment in the use of narrow-band space photography in the study of earth resources carried out in July-August 1985 on board the Salyut-7 space station is described. Exposure of photographic film highly sensitive to reflected and emitted radiation for 10-nm-wide spectral bands that maximize contrast between particular natural features and their surroundings provides an effective means for increasing the accuracy of recognition of such features as ring structures, condition and species composition of plant communities, agricultural crops, and turbid and polluted waters in seas and lakes. Translated from: Geodezlya i kartografiya, 1986, No. 4, pp. 19-27.     

水色遥感中偏振信息的研究进展

介绍了目前水色遥感中,水面反射光的偏振特性及其应用与水体散射光的偏振特性及其应用的研究进展.着重分析了基于偏振原理的水面反射光的剥离、海面溢油偏振遥感探测与基于水体物质偏振信息的水质参数反演等几个问题的研究现状;总结了在水色遥感信息流中,大气偏振校正、气-水界面偏振描述、基于偏振水质遥感反演、传感器偏振响应标定等各个环节入射光与出射光的偏振改变与响应机制等几个关键问题.     

全天空偏振模式及其影响因素初探

太阳光入射与地表、大气相互作用,会在天空中出现较为稳定的天空偏振模式图,即以太阳为中心,天空中的偏振信号呈现一定的规律分布。影响天空偏振模式图的强度及形态主要由地表反射性质、空气分子散射性质及气溶胶光学性质共同影响。本研究利用矢量辐射传输模型,以海洋下垫面为例,在获取沙尘非球形与煤烟非球型气溶胶单次散射性质的基础上,模拟了不同气溶胶光学厚度情况下的全天空偏振模式图。结果表明,天空以太阳入射方向为中心呈现一个较为稳定的天空偏振模式图。沙尘型散射气溶胶光学厚度的增大会减弱该模式图的强度,而煤烟型吸收气溶胶光学厚度的增大会增大该模式图的强度。利用双模态(沙尘型与煤烟型混合)气溶胶模型,系统分析不同气溶胶比例情况下的天空偏振模式图,结果表明全天空偏振模式图的基本模态依旧存在,但是其强度受气溶胶模型与光学厚度双重影响。因此在利用全天空偏振模式图进行气溶胶光学性质反演时需要注意气溶胶模态信息的选择。     

INTERPRETATION OF ECOLOGICAL-SOIL CHARACTERISTICS OF WOODED STEPPE ZONE IN THE CENTRAL RUSSIAN UPLAND

The authors describe how remote sensing imagery can be employed in the identification of different types of chernozem soils in a predominantly agricultural zone (forest steppe), where natural vegetation (normally one of the best vegetation indicators) has been largely displaced by farm fields. A multi-stage methodology is outlined whereby small-scale imagery is used to delineate large regions of similar bioclimatic-geologic characteristics, from which areas of similar soil formation conditions are distinguished. Multispectral and multitemporal space imagery then is employed to detect less salient ecological-soil differences that can affect phototone and image texture. Translated by Edward Torrey, Alexandria, VA 22308 from: G. V. Dobrovol'skiy and V. L. Andronikov, eds., Aerokosmicheskiye metody v pochvovedenii i ikh ispol'zovaniye v sel'skom khozyaystve: sbornik nauchnykh trudov [Remote Sensing Methods in Soil Science and Their Utilization in Agriculture: A Collection of Scientific Works]. Moscow: Nauka, 1990, pp 103–109.     

水稻叶片最优叶肉结构参数估算

叶片作为植物冠层的基本组成元素,其自身的光学特性直接影响着遥感所能获得的植物冠层反射光谱。从原理上讲,叶片的光学特性不仅取决于其内部生化组分含量的多少,还与其物理结构密切相关。因此对叶片内部物理结构进行估算有助于分离其对叶片光谱的影响,从而提高叶片生化信息反演的精度。在基于叶片内部辐射传输过程的PROSPECT模型中,叶片内部结构用一个假想的叶肉结构参数N来描述。PROSPECT模型模拟光谱发现,N对叶片反射率和透过率均影响显著,且影响范围涵盖400—2500nm的全部波段。本文利用水稻叶片实测光谱和生化数据尝试了3种N的估算方法,包括两种经验方法和一种模型反演方法,并对其进行比较。结果表明,由于两种经验方法都基于N和表观叶面积（SLA）之间的非线性经验公式,因此两者具有内在的数学关系。运用模型反演方法估算的N可在实测水稻光谱和模型模拟光谱间得到最小RMSE,且其在数值上小于两种经验方法的估算值。以N为因变量,叶片光谱反射率为自变量,运用逐步线性回归分析建立了N的光谱估算模型,550nm,816nm,1210nm和1722nm四个波段被选入模型,回归效果较好,为N的估算提供了一种新的经验方法。