月球表面微波主被动遥感的建模模拟与反演

探测月球和其它外星球是我国空间遥感与深空探测的又一轮新课题。研究地球遥感中星载被动遥感辐射计、主动遥感高分辨率合成孔径雷达等如何应用于月球和其它外星球的探测是一项十分有意义的工作。了解月球表层的月壤与月岩的物质状态及其分布,对于月球资源的科学认识、以及未来月球探测、登月与月球开发,以及其它外星球探测均具有十分重要的意义。先讨论微波被动遥感月球表面辐射的模拟和由微波辐射反演月壤厚度。由月球表面数字高程和月壤厚度实测点数据建立月球表面高度与月壤厚度的一种对应关系,构造整个月球表面月壤厚度的试验性分布。根据克莱门汀的紫外可见光光学数据,计算整个月球表面月壤中FeO+TiO2含量分布,给出整个月球表面月壤介电常数分布。由月球表层温度的观测结果以及月壤的导热特性,给出月尘层与月壤层温度随纬度分布的经验公式。在这些条件基础上,建立月尘、月壤、月岩3层微波热辐射模型。由起伏逸散定理,模拟计算月壤低耗散介质层多通道辐射亮度温度。以此辐射亮度温度模拟加随机噪声为理论观测值,按3层模型提出月壤层厚度反演方法。由于高频通道穿透深度小,由高频通道的辐射亮度温度按照两层尘-月壤微波热辐射模型反演月尘层与月壤层的物理温度。并以此为已知参数,由穿透深度较大的低频通道的辐射亮度温度反演月壤层厚度,对于反演的相对误差也进行了讨论。在研究微波主动遥感方面,提出低空飞行全极化L波段雷达窄脉冲探测月壤层厚与层结构的建议。此时采用一层具有上下随机粗糙界面的有耗
介质层月壤层模型,在下垫月岩粗糙界面上有一层随机分布的碎石散射体。推导了包含面散射、体散射,以及面体相互作用7种散射机制的全极化脉冲波Mueller矩阵解。以月壤特征参数(月壤层厚、FeO+TiO2金属含量、介电常数,界面粗糙度、碎石分布等)为函数,用时域Mueller矩阵解数值模拟来验证方法可行性。L波段窄脉冲极化回波波形能用于反演或估算月壤厚度与分层结构。

Modeling Simulation and Inversion for Microwave Active and Passive Remote Sensing of the Lunar Surface

Passive and active microwave remote sensing for the lunar regolith media are studied.Based on currently available digital elevation mapping(DEM) and some measurements of lunar regolith layer thickness at Apollo landing sites,a correspondence of the lunar regolith layer thickness to the lunar DEM is proposed to construct the global distribution of lunar regolith layer thickness.Using Clementine UVVIS multispectral data,the global spatial distribution of FeO TiO2 content on the lunar regolith layer is calculated.Thus,dielectric permittivity of global lunar regolith layer can be obtained.Based on some measurements of physical temperature of the lunar surface,an empirical formula of physical temperature distribution over the lunar surface is presented.Based on aforementioned works,brightness temperature of lunar regolith layer in passive microwave remote sensing,which is planned for China's Chang-E lunar project,is numerically simulated by a three layer model using fluctuation dissipation theorem.When these simulations as observations are obtained,an inversion approach of the lunar regolith layer thickness is developed.Because the penetration depth is small for the areas with high FeO TiO2 content,the emission contribution from underlying lunar rock becomes negligible at high frequency channels,19.35 GHz and 37.0 GHz.Under this situation,the temperature of the top layer and the lower regolith can be inverted by the brightness temperature at these two channels using a two-layer model.Taking those points with high FeO TiO2 content along each latitude as the reference points,the temperature variation with the latitude of top layer and the lower regolith layer can be inverted.Then,taking the inverted temperature as a known parameter,the regolith layer thickness can be inverted by the brightness temperature at the channel 3.0 GHz.Numerical simulation and inversion approach in this paper make an evaluation of the performance for lunar passive microwave remote sensing,and for future data calibration and validation.To explore the potential utilities of lower frequency radar pulse for lunar exploration,a theoretical model of lunar regolith layer and numerical simulation of polarimetric radar pulse echoes are developed in this study.The lunar regolith layer consist of the regolith layer with the randomly rough interfaces at the top and bittom of the regolith layer,and a layer of random discrete stones is laid over the lunar rock media.The time domain Mueller matrix solution is derived from vector radiative transfer,and is applied to numerical simulation of polarimetric radar pulse echoes from the stratified random media.The Mueller matrix solution contains seven scattering mechanisms of the stratified media: surface scattering from the rough interfaces,volumetric scattering from random stone scatterers(non-spherical scatterers are assumed),and their multi-interactions.As the radar pulse at L band is penetrating through the random surface,attenuation through the low loss regolith medium,polarimetric scattering through the stone scatter medium and rough surfaces are formulated in our Mueller matrix solution.Model parameters are set according to the study of the lunar regolith structure.Temporal characteristics and structure of the polarimetric echo profile are analyzed.It consists of a prominent peak due to the top boundary scattering and a complex tail due to the bottom boundary and stone volumetric scattering.Contributions of different scattering mechanisms,i.e.surface,volumetric scattering and interactions,are analyzed,and their dependence on model parameters such as the layer thickness and the content of FeO TiO2,are also discussed.Simulation of pulse echoes might display a image of underneath structures.It reveals information of the depth and other properties of the lunar regolith layer,and demonstrates a potential new way to explore moon surface in future.