嫦娥四号着陆区次表层介电特性全波形反演与仿真验证

Numerical Validation of Subsurface Dielectric Property Estimation Based on Full Waveform Inversion at Chang’E-4 Landing Site

介电特性是决定雷达波在物质中传播速度的重要参数.嫦娥四号测月雷达提供的高垂向分辨率次表层雷达剖面信息有助于加深对月球次表层物质介电特性的理解与认识.全波形反演法充分利用雷达波场的运动学和动力学信息,根据雷达波模拟结果与真实数据的差异计算更新参数,迭代初始介电模型实现对次表层介电剖面的反演.本文结合嫦娥四号测月雷达数据与时域有限差分方法下均质模型和随机等效介质模型的雷达回波特性,确定随机等效介质模型能够更好地模拟嫦娥四号着陆区次表层物质的介电特性.全波形方法反演的介电模型与真实模型在大部分区域的相对介电常数误差小于0.2,为反演月壤厚度及构建次表层温度模型提供了重要的数据支撑.

Dielectric property is an important parameter that determines the propagation speed of radar wave in materials,which is widely used in stratigraphic division,regolith thickness inversion,radar model construction and water-ice detection.However,continuous impacts may cover the traces of impor-tant geological activities and hinder the exploration of lunar geological.In January 2019,China’s Chang’E-4 carried the Yutu-2 rover successfully landed at the Von Kármán crater(177.5991°E,45.4446°S)in the South Pole-Aitken(SPA)basin.The Yutu-2 rover equipped with dual-frequency ground penetrating radar(Lunar Penetrating Radar,LPR).The subsurface radar diagram with fine ver-tical resolution provided by the Chang’E-4 LPR can deepen our understanding of the dielectric property of lunar subsurface materials.Full Waveform Inversion(FWI)method can fully utilize the kinematic and dynamic information of radar wave field and invert the dielectric property by constructing an initial di-electric model and continuously updating this model with comparison of the observed radar data.By comparing the simulation results of homogeneous dielectric model and stochastic equivalent media mod-el to the Chang’E-4 LPR diagram,we selected the stochastic equivalent media model as the real model to simulate the subsurface dielectric profile at the Chang’E-4 landing site and valid the dielectric accura-cy inversed by FWI method.Our results reported that FWI method can not only capture the dielectric perturbation in local scale,but also generate two-dimensional dielectric profile with high spatial resolu-tion.The initial dielectric model is able to better characterize the dielectric properties after 79 FWI itera-tions,and the maximum inversion error of relative dielectric constant is limited to 0.2(the objective function is minimized to 0.91%of the initial value).The stochastic equivalent medium model can effec-tively simulate the dielectric properties of the lunar regolith,and the radar simulation results based on it are close to the Chang’E-4 LPR radar diagram.