基于测月雷达数据的月球次表层地质构造反演研究

Observations of the subsurface geology of the Moon help advance our understanding of lunar origin and evolution. The LPR (Lunar Penetrating Radar), which will be the first ground penetrating radar working on the planetary surface, is one of the most important payload onboard the Lunar Rover of the Chang'e-3 mission. The primary goal of the LPR is to detect the lunar regolith depth and subsurface geological structure on its route. LPR data reflect the impedance differences of lunar subsurface medium, which is not only decided by the dielectric constant, conductivity and magnetic permeability, but also gave rise to the inhomogeneous medium, multiple reflections and environment reflection, etc. According to the ground-penetrating radar analysis methods in the Earth exploration, a forward response model is established here based on the priori knowledge of the lunar subsurface structure. Adjusting the model parameters, the the lunar subsurface geological structure is obtained by comparing the forward response model to LPR data. Verifications will be carried out based on the ground test data of LPR, which can help the lunar subsurface geological structure inversion in the future.

月球次表层的地质构造对研究其起源和演化历程非常重要。测月雷达搭载在嫦娥三号月球表面巡视器上，是人类首次采用表面探地雷达的方式进行月球次表层地质构造探测，其探测目的是获取巡视路线上的月壤厚度和月壳浅层结构。测月雷达数据反映了月球次表层介质的阻抗差异，是介电常数、电导率和磁导率差异的综合体现，另外还由于介质非均匀性、多次反射、环境反射等的影响，不可避免的存在多解性和复杂性。我们拟借鉴探地雷达在地球探测中分析方法，根据对月球次表层结构的先验知识建立正演模型模拟计算雷达回波，将其与实测回波进行拟合分析，通过调整正演模型参数完成对月球次表层地质构造的反演计算。结合旱地冰川、冰湖以及模拟月壤地区的地面试验数据，我们可以对该反演算法进行验证，为将来测月雷达的月球次表层地质构造反演分析做准备。

月球次表层的地质构造对研究其起源和演化历程非常重要。测月雷达搭载在嫦娥三号月球表面巡视器上，是人类首次采用表面探地雷达的方式进行月球次表层地质构造探测，其探测目的是获取巡视路线上的月壤厚度和月壳浅层结构。测月雷达数据反映了月球次表层介质的阻抗差异，是介电常数、电导率和磁导率差异的综合体现，另外还由于介质非均匀性、多次反射、环境反射等的影响，不可避免的存在多解性和复杂性。本项目借鉴探地雷达在地球探测中分析方法，根据对月球次表层结构的先验知识建立了四层非均匀正演模型，采用时域有限差分（FDTD）数值模拟方法，模拟了测月雷达电磁回波，并与部分实测数据对比分析，反演月球次表层地质构造。通过对比两者B-Scan回波信号与A-Scan回波信号，调整模型参数，验证了正演模型较为符合真实月壤内部的结构，月壤层内部不是纯一的月壤介质，而是分布着大量大小不均、形态各异的月岩颗粒等介质。有效支撑了CE-3测月雷达数据解译工作，并为后续CE-5测月雷达的数据解译工作提供技术储备。