“嫦娥一号”对月球新生环行山表面热辐射“热点”与“冷点”昼夜变化的观测

20世纪60年代由地基观测的月球表面红外辐射扫描图像发现月蚀过程中月表面有大量的异常"热点",而在"嫦娥一号"(CE-1)对月球表面微波辐射亮度温度(Tb)观测中,这些红外辐射"热点"的地方恰是夜间微波热辐射的"冷点".本文以辐射传输理论分析,解释了这些热辐射昼夜变化很大的异常现象.为比较月表面昼夜辐射温差的变化,选取了在相近纬度上两种典型的环形山区域:一是表面有大量离散岩石块分布的代表新生的环形山(第谷Tycho Crater),另一是经历了长期陨石冲击粉碎与月质演变的不再有大量岩石块分布的老年环形山(莫洛利卡斯Maurolycus Crater).给出了这两环行山区域的CE-1微波Tb数据的昼夜变化,并与美国2009年月球轨道勘测器"先知者"(Diviner)探测对应的红外辐射做了对比.以月表3层模型的辐射传输为基础,从CE-1Tb数据反演了该两区域月壤介质层物理温度的昼夜变化及其分布将月表面物理温度昼夜变化与红外观测结果做了比较.可以看出,月表面热辐射与物理温度的昼夜变化分布,及其"热点"与"冷点"的变化与月表面新生环形山大量分布的高热传导高热惯性岩石块丰度(abundance)分布密切相关.     

MATLAB在微波探测仪数据处理中的应用

星载微波探测仪是嫦娥一号卫星有效载荷之一.主要用于测量不同深度的月壤微波辐射亮温,进而反演月壤厚度的信息并对月球的氦-3资源量和分布进行评估.为了监测某段时间微波辐射计工作是否正常,我们需要对辐射计下传的大量数据按工程要求进行处理.MATLAB应用软件以其强大的科学计算和可视化功能成为了微波探测仪数据处理工具之一.本文结合微波探测仪工程实例,编写了MATLAB数据处理程序,并比较分析了两种MATLAB数据读取的方法,从而总结得出一种提高MATLAB大批量数据处理效率的方法.     

微波月亮-人类对月球的全新视角——中国“嫦娥一号”卫星微波探测仪若干探测结果

中国“嫦娥一号”探月卫星自2007年10月24日成功发射并于同年11月7日进入其工作轨道。在轨工作一年多,完成了全部使命,期间获取了大量的科学数据。其中“嫦娥一号”月球微波探测仪(Chang’e-1 Lunar Microwave Sounder-CELMS)已多次覆盖全月表面,首次获取了全月微波亮温分布数据,创建了“微波月亮”(Microwave Moon-MicM)。“微波月亮”的建立为月球科学研究、宇宙科学研究、月球资源研究及应用、未来月球基地的建立等带来了全新的信息,与“可见月亮”、“红外月亮”及其它相关探测结果(如X、γ谱仪,中子谱仪)、地基探测及未来月球轨道上观测和就位探测等多方信息的融合、分析,将大大提升人类对太空、月球及宇宙起源、生命起源等问题的认识和研究水平,在人类探月活动中具有里程碑意义。
在“嫦娥一号”卫星微波探测仪绕月探测之前,从来没有从月球轨道对全月球进行微波探测的活动。很多涉及月球微波特征研究,如月表微波亮温分布、月壤厚度及氦-3资源量分布信息、涉及月球历史等的研究多数是靠Apollo、Luna的落月点实测数据为依据,加上其它探测(如光学等)结果融合分析并逻辑延伸而得来的,因此其结果存在相当的多解或不确定性,这就使我们对月球微波辐射特性的真实情况了解很少,甚至可能有偏差。着重讨论“微波月亮”的含义,其相关信息内涵,几种特征区、点的分析等。根据微波探测仪的数据,获得了全月月壤厚度分布、氦-3资源量评估、全月亮温及其变化规律等研究结果,得出了一些与现今其它研究结果不同的结论。     

全极化微波信号海面风场反演技术现状与发展趋势

全极化微波辐射计是一种新型的被动微波遥感仪器,可以测量海面辐射的全部4个Stokes参数,提供了测量海面风场的一种新方法。首先介绍了国内外先进微波辐射计的技术特点及其海洋遥感应用情况,然后描述了海面微波发射信号的变化机理,以及海面全极化信号的风向谐波特征及其反演海面风场的优势,归纳了全极化微波信号海面风场反演的总体技术思路和产品精度,最后分析了全极化微波辐射计风场反演的关键技术和难点,并对该项技术的发展进行了展望。     

林下枯枝落叶层双频段微波辐射衰减特性研究与分析

林下枯枝落叶层会衰减来自土壤的微波辐射信号,降低微波辐射亮温对地表参数变化的敏感性,从而影响林下地表参数的反演精度。为了定量研究枯枝落叶层的衰减特性,基于τ-ω模型,通过严格的理论推导证明了利用不同厚度下的枯枝落叶层亮温计算衰减系数的可行性,并基于该理论方法设计可控实验,获取了双频段(18.7GHz和36.5GHz)上不同厚度、不同重量含水量的枯枝落叶层亮温值,然后定量分析了枯枝落叶层的衰减系数随重量含水量的变化过程,同时根据计算的消光系数,分析了不同厚度、不同重量含水量下的枯枝落叶层透过率。结果表明:较干燥的枯枝落叶层的衰减系数较小,透过率较高,但是随着含水量增大,衰减系数会出现急剧的增加,从而造成透过率骤减;高频波段的衰减系数变化更加迅速,由枯枝落叶层引起的衰减作用更加明显;单次散射反照率ω随重量含水量的变化趋势为先升高后降低。该研究有利于理解森林系统中微波辐射传输过程,纠正森林区微波辐射亮温,提高森林下地表参数遥感反演精度。     

全极化微波辐射计扫描目标成像方法研究

微波辐射计是被动遥感仪器,对人体无害,这使其对人体辐射信息成像具有很大的优势。全极化微波辐射计可以通过测量目标的4个Stokes参数得到目标的全部极化信息,这对人体亮度温度分布的测量和分析是一种有效的补充,使全极化辐射计在医学方面的应用成为可能。基于上位机软件控制的二维扫描平台,设计出一套软件控制与成像方法,控制全极化辐射计对目标进行平面扫描,得到目标的辐射亮温图像。使用37GHz的全极化辐射计进行在近场条件下的人体扫描成像实验,得到了T_v、T_h、T_3、T_44个通道的人体量温图像,验证了全极化微波辐射计扫描人体成像方案的可行性。     

“嫦娥一号”五大关键技术

10月24日晚，我国第一颗绕月探测卫星——嫦娥一号发射成功并进入预定地球轨道。 此次嫦娥一号绕月探测飞行将完成四大科学探测任务；获取月球全表面三维图像；分析月球表面化学元素和物质类型的含量和分布；探测月壤特性；探测4万至40万公里间地月空间环境。     

东北地区森林积雪的微波辐射亮温模拟分析

微波辐射亮温正向模拟是辐射传输模型反演积雪参数的关键步骤之一。以HUT模型为基础,针对森林冠层微波透过率这一关键的模型输入参数,在东北大小兴安岭典型森林积雪区进行了14个子区域(10km!10km)的地基遥感观测和森林参数取样观测实验,分别利用地基微波辐射计实测和森林材积量回归两种不同参数获取方法,得到实验观测区冬季森林透过率,并模拟了星载微波辐射计探测亮温(TsimuB)。通过对两种参数获取方法模拟亮温的相关性分析,说明在K波段水平极化条件下森林存在体散射效应(相关系数R2≤0.37),而Ka波段双极化和K波段垂直极化条件下,森林存在很弱或无体散射效应(相关系数R2≥0.53)。在此基础上,将TsimuB与FY3C MWRI观测的微波辐射亮温进行了差值比较,以MWRI的定标精度约以2 K为基准,提出了以偏差|Δ|≤3·"=6K为一致性判据准则。在K波段水平极化(H)与垂直极化(V)辐射计模拟的一致性为79%、82%,Ka波段的H和V为43%、50%;材积量模拟亮温的一致性是K波段H和V为57%、86%,Ka波段的H和V均为64%。结果表明:在HUT模型模拟森林积雪系统微波辐射亮度温度时,Ka波段积雪层散射引起的不确定性大于K波段森林散射引起的不确定性。通过数据分析,提出了HUT模型的适用性及东北地区森林—积雪真实性检验场的选址依据。     

AMSR-E数据散射与极化指数检测2008年1月中国南方冰雪灾害

全天候全天时微波遥感是监测自然灾害的重要手段。星载被动微波遥感测量的多通道辐射亮度温度对全球和区域性天气与气候、大气降水、陆地水文、海面风场等物理信息的获取已发挥了重要的作用。2008年初中国通常温暖的南方发生暴雪和冰冻灾害,用业务运行的多通道辐射亮度温度算法产品却无法识别这一冰雪灾害。通过对积雪层的矢量辐射传输模拟,根据多通道微波扫描辐射计AMSR-E数据的散射与极化特征指数、往年同时期同地区正常条件下的平均特征指数以及先时特征指数的变化,构成新的判据流程,能有效地识别中国南方区域性冰雪自然灾害。     

地形坡面对被动微波遥感影响的试验研究

地表起伏所形成的倾斜表面,特别是在山区,受地形坡度和坡向变化的影响,地表的微波辐射特征较之平坦地表发生明显变化。基于地基微波辐射地形试验,模拟星载被动微波辐射计AMSR\|E的观测参数,通过建立地形坡面的地貌微缩景观进行观测,探索地表斜坡对被动微波辐射特征的影响,用AIEM模型 和 Fresnel 方程分别模拟裸土地形坡面的微波辐射特征。结果表明,倾斜坡面对被动微波辐射的亮度温度产生了10~15 K的偏差,由坡度形成的本地入射角改变了地表的有效发射率,并随坡向的变化发生微波极化旋转。经试验数据和模型模拟结果对比,认为AIEM 在考虑了表面粗糙度影响时可以较好地模拟地形坡面的被动微波辐射特征。     

SAR imaging simulation for an inhomogeneous undulated lunar surface based on triangulated irregular network

Based on the statistics of the lunar cratered terrain, e.g., population, dimension and shape of craters, the terrain feature of cratered lunar surface is numerically generated. According to the inhomogeneous distribution of the lunar surface slope, the triangulated irregular network (TIN) is employed to make the digital elevation of lunar surface model. The Kirchhoff approximation of surface scattering is then applied to simulation of lunar surface scattering. The synthetic aperture radar (SAR) image for comprehensive cratered lunar surface is numerically generated using back projection (BP) algorithm of SAR imaging. Making use of the digital elevation and Clementine UVVIS data at Apollo 15 landing site as the ground truth, an SAR image at Apollo 15 landing site is simulated. The image simulation is verified using real SAR image and echoes statistics. Supported by the National Matural Science Foundation of China (Grant No. 40637033)     

基于Krogager分解和SVM的极化SAR图像分类

目标分解包括基于Sinclair矩阵的相干目标分解和基于Mueller矩阵的部分相干目标分解,Krogager分解即属于相干目标分解,它可以将任一对称Sinclair矩阵分解为球散射体、二面角散射体和螺旋体3个分量,这是极化合成孔径雷达(Synthetic Aperture Radar,SAR)图像特征提取的有效途径。把3个分量的分解系数作为极化散射特征,由其组成样本向量,运用基于统计学习理论的支持向量机(Support Vector Machines,SVM)设计多类分类器,提出了一种极化SAR图像分类算法,并对实测极化SAR数据进行分类实验。结果表明,将Krogager分解和SVM分类器结合起来,对极化SAR图像进行分类是可行和有效的,并且选择不同的参数得到的分类结果差别很大,验证了参数选择在SVM分类器中的重要作用。     

A unitary Mueller-based view of polarimetric SAR oil slick observation

Synthetic aperture radar (SAR) oil slick observation is a topic of great applicative relevance which has been physically recast by a set of new polarimetric approaches that exploit the departure from Bragg scattering. In this article, under a unitary Mueller-based view, all the approaches are revisited and reformulated in terms of Mueller matrix elements. This new view is of theoretical and applicative relevance because it allows us to ‘unify’ the output parameters in the same range and, therefore, makes possible a fair ranking of these approaches.     

利用微波辐射计对月壤厚度进行研究

介绍了运用并矢Green函数和起伏逸散定理来计算平面分层媒质的辐射亮温，同时利用最小二乘法对多通道辐射计的模拟测量结果进行处理得到分层媒质厚度的方法。将该方法应用于月壤厚度的反演研究，在假定月壤如平面分层结构模型的情况下，得到了其厚度的反演结果，并对反演误差原因进行分析。     

Characterization of the coherent scattering induced by ridging patterns in agriculture by the use of polarimetric SAR imagery

This article investigates the scattering characteristics of ridging patterns in agriculture by the use of C-band polarimetric synthetic aperture radar (PolSAR) images. The polarimetric signatures of periodic potato fields and row wheat in different directions are highlighted using a set of polarimetric parameters. Enhanced coherent scattering is observed when the alignment direction of the ridging patterns is perpendicular to the radar’s line of sight (LOS). The dominant backscattering mechanism of the ridging patterns is deduced by evaluating different polarimetric parameters. The increased copolarized backscattering coefficients and copolarized correlation coefficient, and the reduced entropy and polarimetric alpha angle, indicate a strong contribution of odd scattering to ridging patterns aligned perpendicular to the LOS. We also compare the dominant contributions to the backscattering of ridging patterns in different phenological stages. Although the canopy changes of potato and wheat with time are significant, the underlying periodic surface changes the dominant scattering mechanism of potato fields over all the phenological stages, and the wheat aligned parallel with the flight direction of radar still has relatively high coherent scattering in the different vegetation development stages. The variability analyses undertake in this study allow a more detailed documentation of the physical scattering process of the ridging patterns in agriculture, and will improve the applicability of synthetic aperture radar images in agriculture.     

基于入射散射极化优化的抗箔条干扰方法

国内外的大多数 研究没有综合考虑入射极化对散射幅度、散射极化的定量影响。通过构建雷达视线方向非相干箔条云瞬时极化散射模型,获得了一组特定入射条件下的极化散射统计数据,并对 其进行基于极化坐标系扭曲的处理,同时讨论了箔条云对入射极化的选择特性。数值仿真结果表明,当扭曲因子较大时,处理后的极化状态概率近似分布在水平极化域,同时雷达俯仰角较小时,箔条云对入射极化具有良好的选择性。本文结论可以作为极化抗箔条干扰的初级优化方案,为极化滤波等后续极化信息处理打下基础。     

The identification of sea swell using polarimetric radars: A new full wave approach

The statistical characteristics and the orientation of a remotely generated swell superimposed upon a local wind generated rough sea surface are determined from computer simulated polarimetric data. The full wave approach is used to determine the incoherent backscatter Mueller matrix elements and the incoherent backscatter Graves power matrix elements as functions of azimuth angle, the colatitude (angle measured from the vertical axis), and rough sea surface (with swell) parameters. The relationships between the incoherent backscatter Mueller matrix as well as the incoherent backscatter Graves power matrix and the statistical characteristics of the swell and its orientation are presented here. On making suitable selections of the backscatter angle and polarization of the Mueller matrix elements or Graves power matrix elements, it is possible to determine reliably the orientation and statistical characteristics of remotely generated swells. Traditionally only the scattering cross sections are utilized in remote sensing.     

Calculations of radar backscattering coefficient of vegetation-covered soils

A model for simulating the measured radar backscattering coefficient of vegetation-covered soil surfaces is presented in this study. The model consists of two parts: the first is a soil surface model to describe the backscattered radar pulses from a rough soil surface, and the second part takes into account the effect of vegetation cover. The soil surface is characterized by two parameters, the surface height standard deviation σ and the horizontal correlation length l. The effect of vegetation canopy scattering is incorporated into the model by making the radar pulse subject to two-way attenuation and volume scattering when it passes through the vegetation layer. These processes are characterized by the two parameters, the canopy optical thickness τ and the volume scattering factor η. The model results agree well with the measured angular distributions of the radar backscattering coefficient for HH polarization at the 1.6 GHz and 4.75 GHz frequencies over grass-covered fields. These observations were made from an aircraft platform during six flights over a grass watershed in Oklahoma. It was found that the coherent scattering from soil surfaces is very important at angles near nadir, while the vegetation volume scattering is dominant at larger incident angles (> 30°). The results show that least-squares fits to scatterometer data can provide reliable estimates of the surface roughness parameters, particularly the surface height standard deviation σ. The range of values for σ for the six flights is consistent with a 2 or 3 dB uncertainty in the magnitude of the radar response.     

Radiative transfer theory for polarimetric remote sensing of pine forest at P band

In this paper, the radiative transfer “RT” theory for clustered vegetation structures is developed and used to interpret polarimetric radar backseattering measurement data from pine forest. The RT theory has been widely used to calculate radar backscattering coefficients from layered geophysical media and to interpret the measurement data. However,the conventional RT theory ignores the relative phase information associated with structured scatterers. which may play an important role in the overall scattering behaviour. To take into account the clustered structures with the RT theory, the scattering function of each cluster is calculated by incorporating the phase interference of scattered fields from each component. Subsequently, the resulting phase matrix is used in the radiative transfer equations to calculate the polarimetric backscattering coefficients from layered random media embedded with vegetation clusters.A multi-scale structure model of pine forest, which includes trunks, primary and secondary branches, is used to interpret and simulate polarimetric radar response at P band “0·44Hz”. The theoretical calculations are shown to be in good agreement with the backscattering data measured at the Landes maritime pine forest during the MAESTRO 1 Campaign.