光学观测与微波辐射模拟对月壤厚度的反演

Inversion of lunar regolith layer thickness using optical data and microwave emission simulation

由月球正面的光学反照率,根据颗粒表面分光反照率的几何光学模型,计算月球正面FeO+TiO2含量的分布。根据月球正面数字高程(DEM,digitalelevationmapping)与FeO+TiO2含量之间的统计关系,由月球背面DEM构造月球背面的FeO+TiO2含量分布。由整个月球表面的FeO+TiO2含量分布,计算月球表面介电常数的分布。依据月球表面温度分布以及由DEM对应构造的月球表面月壤厚度,由起伏逸散定理,模拟计算了3,7.8,19.35,37GHz四个通道平行分层月壤微波辐射亮度温度的月球表面分布。以此模拟分布为理论观测值,提出三通道—两通道相结合的月壤厚度反演方法。当FeO+TiO2含量较低,各通道辐射亮度温度有差异时,采用三通道方法反演月壤厚度;当FeO+TiO2含量过高,使得高频7.8,19.35,37GHz的辐射亮度温度由于饱和而趋于相同时,采用两通道方法反演月壤厚度。若金属含量过高,而可能使四个通道辐射亮度温度都不易区分时,由FeO+TiO2含量可以确定出月壤厚度的下限值。为现有的多通道微波探月提供一个可行的月壤厚度反演方法,也有助于月球表面辐射亮度温度的定标与验证。

Albedo of lunar nearside at the wavelengths 0.42, 0.65,0.75, 0.95μm from the telescopic observation is employed to construct the spatial distribution of the FeO＋TiO2 on the lunar regolith layer. A statistic relationship between the DEM and FeO＋TiO2 content of lunar nearside is extended to construction of FeO＋ TiO2 content of lunar farside. Thus, the dielectric constant of the regolith layer for whole lunar surface can he determined. Based on the correspondence of the DEM and lunar regolith layer thickness, and employing the physical temperature distribution over lunar surface, brightness temperature of lunar regolith layer is numerically simulated by a parallel layer model using the fluctuation dissipation theorem.Furthermore, taking these simulations as observations, an inversion method of lu- nar regolith layer thickness is developed by using three- or two-channels brightness temperatures, When the FeO＋TiO2 content is low, and the four channels brightness temperatures are well distinguishable, the regolith layer thickness and physical temperature of the underlying lunar rocky media can be inverted by the three-channels approach, When the FeO＋TiO2 content is so high that the brightness temperature at the 19.35, 37GHz channels might be saturated, the regolith layer thickness has to be inverted only by the two-channels approach. Numerical simulation and inversion approach in this paper make an evaluation of the performance for lunar remote sensing, and for future data calibration and validation.