基于嫦娥测月雷达数据的月球正、背面次表层结构模型与演化研究

Lunar penetrating radar (LPR) data acquired by the rovers of Chang 'e-3 and Chang 'e-4 can be used to image lunar subsurface structures to build geological evolution models for the near side and the far side of the Moon, which will provide clues for the formation mechanism of the "dichotomy" on the surface of the Moon. The main difficulties and problems in this study are as follows: 1) Conventional radar imaging is usually unable to detect structures accurately and reliably based on the radar data with the interferences of irregular working path, non-uniform interval acquisition. 2) As soft landing and exploring on the far side of the moon is the first time in history, some special geological information of the landing site should be included to analyze the subsurface structure on the far side of the Moon and the differences from the results of the near sides of the Moon. To complete these tasks, this project adopts the method of least square to conduct the migration imaging, which is used to overcome the problem of irregular interference. In this method, the migration imaging is taken as an inversion problem, solved by iterative matching between migrated synthesized radar data based on a three-dimensional surface model and the migration results of the actual observed data, working out more accurate and reliable subsurface structure and electrical parameters. Then, this project will analyze the material source and the lithology of the landing area according to the characteristics of subsurface structure and the physical property parameters. In addition, the time series of chronostratigraphic unit and the evolution model will be built, combined with the surrounding geological information and other exploring methods. By comparing and analyzing the subsurface structure and the evolution rules of the areas on the near side and the far side of the moon, the evolution model of the subsurface layer on the Moon will be constructed.

利用嫦娥四号和嫦娥三号测月雷达数据，对月球次表层进行成像研究，构建月球正、背面的地质演化模型，为探讨月表“二分性”特征的形成机制提供科学依据。本研究的主要困难和问题有：1）常规的二维偏移方法是研究直测线形成的雷达剖面，难以解决测月雷达探测路径不规则、非等间距采集等问题，导致无法获取准确、可靠的地下结构；2）嫦娥四号首次在月球背面软着陆探测，因此需要结合着陆区的特殊地质环境，深入分析月球背面的次表层结构及其与月球正面探测结果的差异性。主要解决方案：采用最小二乘偏移成像克服非规则性干扰问题。该方法是将偏移当作反演问题求解，通过构建三维曲面模型得到合成雷达剖面及其偏移结果，与实测数据偏移结果进行迭代对比，获取更为正确、可靠的次表层结构和电性参数。综合周边地质信息以及其他探测手段，分析着陆区的物质来源和岩性，构建地层年代序列与演化模型。最后，对比分析月球正、背面探测区域的次表层结构特征和演化规律。

本项目利用嫦娥三号和嫦娥四号的测月雷达获取的电磁波数据，分别对月球正、背面着陆区的月壤以及次表层结构进行了多尺度成像研究。研究发现月球正面雨海北部的年轻玄武岩具有更细的分层结构，表明该地区的爱拉托逊纪熔岩流具有多期性。在月球背面冯·卡门撞击坑内识别出了分层结构和一些特殊的地质构造，包括较厚的月壤层、掩埋地质体、撞击溅射层以及多期熔岩层等。由此表明冯·卡门撞击坑经历了间歇性的火山活动。再结合区域地质信息，分析和推测了这些次表层物质的沉积序列和演化过程。最后，根据雷达成像结果，结合着陆区周边地质信息，分别构建了月球正、背面的次表层演化模型，并针对月壤厚度、多期熔岩流、撞击溅射等特殊的月球演化事件进行了对比分析，得到了月球正、背面次表层的演化特征以及差异性，为月球的二分性演化理论提供了重要依据。