雷达探测仪对月球次表层结构探测的理论建模与反演方法
发布时间：2019-03-17 12:50
【摘要】： 月球是地球的唯一一颗天然卫星,它的内部结构是一直人类不断探索的谜题之一。在漫长的月球历史中,由于受到陨石小天体的撞击以及太阳-宇宙射线的照射,月球表层储存了月球地质和太阳辐射活动的线索。研究月球的结构有助于提高对月球资源的科学认识,对于未来的探月、将月球作为人类探测更遥远天体的理想平台等有着十分重要的意义。 在月球探测中,星载高频雷达探测仪(Radar Sounder)是一种用于探测月球次表层结构的有效工具。与其它微波频段相比较,高频波段(3-30MHz)的电磁波可以穿透到月表以下几百米至几千米的月表深层,从而可以揭示出月球次表层结构特征。雷达探测仪接收到月球表层的回波主要有：表面天底点回波,表面非天底点回波和次表面天底点回波。高频雷达探测仪主要通过表面天底点和次表面天底点回波的时延差和强度来判断月球次表层的深度以及物质成分。 本文首先讨论了高频雷达探测仪频率与带宽的选取准则,介绍了基于粗糙面电磁散射的Kirchhoff近似与几何光学射线追踪方法对月表雷达回波的快速模拟方法。在雷达探测仪对月球次表层结构探测的回波模拟中,由于选取的月球表面及次表面都是有限的,会使得月球表面及次表面场景边缘所对应的射程距离处产生虚假的峰值回波。因此在模拟中,需要在边缘对应的射程距离处对接收到的回波进行截断。作为本研究的第一个问题,本文讨论了回波截断处所对应的射程距离与月表层参数之间的定量关系。 电磁波在月球次表层内部传播过程中受衰减、透射、散射等影响,次表面天底点回波往往会很微弱。受月球表面粗糙度、环形山等月表地形的影响,来自表面非天底点的强杂波往往会淹没微弱的次表面回波,成为对月球次表层结构探测的最大障碍。对于如何从具有强烈背景杂波的雷达探测仪回波中提取微弱次表面回波的研究,到目前为止还比较少。为有效探测月球次表层结构,本文基于月球次表面天底点回波和表面非天底点回波(杂波)的相干与非相干特性,提出在月球次表面地形变化不大的情况下,由累积取平均的方法来抑制表面非天底点回波从而识别次表面回波。以数值模拟的月海与月陆表面雷达探测仪回波为例,验证了该方法的正确性与可行性,并讨论了累积平均数目对次表面回波提取结果的影响。 本文所述方法也可以应用到火星等其他外星球次表层结构、以及液态水的探测中。
[Abstract]:The moon is the only natural satellite on Earth, and its inner structure is one of the mysteries that mankind has been exploring. In the long history of the moon, the lunar surface has stored clues to lunar geology and solar radiation activity because of the impact of meteorite small objects and the irradiation of solar-cosmic rays. The study of the structure of the moon is helpful to improve the scientific understanding of the lunar resources. It is of great significance for the future exploration of the moon as an ideal platform for human exploration of distant objects. In lunar exploration, the spaceborne high frequency radar detector (Radar Sounder) is an effective tool for detecting the subsurface structure of the moon. Compared with other microwave frequencies, the electromagnetic waves in the high frequency band (3-30MHz) can penetrate the deep layers of the lunar surface hundreds to thousands of meters below the lunar surface, thus revealing the structural characteristics of the subsurface layer of the moon. The echoes of the surface of the moon are mainly received by the radar detector, including the surface celestial point echo, the surface non-celestial point echo and the sub-surface celestial point echo. The depth and material composition of the subsurface layer of the moon are judged mainly by the delay difference and intensity of the echoes of the surface sky-bottom point and the sub-surface sky-bottom point by the high-frequency radar detector. In this paper, we first discuss the selection criteria of frequency and bandwidth for high frequency radar detectors, and introduce a fast simulation method for lunar radar echoes based on Kirchhoff approximation and geometric optical ray tracing method based on rough surface electromagnetic scattering. In the echo simulation of the lunar subsurface structure detected by the radar detector, the false peak echo will be generated at the range distance corresponding to the lunar surface and the sub-surface scene edge because the selected lunar surface and sub-surface are limited. Therefore, it is necessary to truncate the received echo at the range distance corresponding to the edge in the simulation. As the first problem in this study, the quantitative relationship between the range distance corresponding to the echo truncation and the parameters of the lunar surface is discussed in this paper. The electromagnetic wave propagation in the subsurface of the moon is affected by attenuation, transmission, scattering and so on. The echo of the sub-surface sky point is often very weak. Under the influence of lunar surface roughness, craters and other lunar topography, the strong clutter from the non-celestial surface often inundates the weak subsurface echoes, which becomes the biggest obstacle to the exploration of the subsurface structure of the moon. So far there is little research on how to extract weak subsurface echoes from radar detector echoes with strong background clutter. In order to detect the subsurface structure of the moon effectively, based on the coherent and non-coherent characteristics of the lunar subsurface celestial point echo and the surface non-celestial point echo (clutter), it is proposed that under the condition that the subsurface topography of the moon does not change much, The method of cumulatively averaging is used to suppress the surface non-celestial echo so as to identify the sub-surface echo. The validity and feasibility of the method are verified by numerical simulation of lunar sea and lunar land surface radar echo, and the effect of cumulative average number on the result of subsurface echo extraction is discussed. The method described in this paper can also be applied to the subsurface structure of other alien spheres, such as Mars, as well as to the exploration of liquid water.
【学位授予单位】：复旦大学
【学位级别】：硕士
【学位授予年份】：2010
【分类号】：P184.5
本文编号：2442316
[Abstract]:The moon is the only natural satellite on Earth, and its inner structure is one of the mysteries that mankind has been exploring. In the long history of the moon, the lunar surface has stored clues to lunar geology and solar radiation activity because of the impact of meteorite small objects and the irradiation of solar-cosmic rays. The study of the structure of the moon is helpful to improve the scientific understanding of the lunar resources. It is of great significance for the future exploration of the moon as an ideal platform for human exploration of distant objects. In lunar exploration, the spaceborne high frequency radar detector (Radar Sounder) is an effective tool for detecting the subsurface structure of the moon. Compared with other microwave frequencies, the electromagnetic waves in the high frequency band (3-30MHz) can penetrate the deep layers of the lunar surface hundreds to thousands of meters below the lunar surface, thus revealing the structural characteristics of the subsurface layer of the moon. The echoes of the surface of the moon are mainly received by the radar detector, including the surface celestial point echo, the surface non-celestial point echo and the sub-surface celestial point echo. The depth and material composition of the subsurface layer of the moon are judged mainly by the delay difference and intensity of the echoes of the surface sky-bottom point and the sub-surface sky-bottom point by the high-frequency radar detector. In this paper, we first discuss the selection criteria of frequency and bandwidth for high frequency radar detectors, and introduce a fast simulation method for lunar radar echoes based on Kirchhoff approximation and geometric optical ray tracing method based on rough surface electromagnetic scattering. In the echo simulation of the lunar subsurface structure detected by the radar detector, the false peak echo will be generated at the range distance corresponding to the lunar surface and the sub-surface scene edge because the selected lunar surface and sub-surface are limited. Therefore, it is necessary to truncate the received echo at the range distance corresponding to the edge in the simulation. As the first problem in this study, the quantitative relationship between the range distance corresponding to the echo truncation and the parameters of the lunar surface is discussed in this paper. The electromagnetic wave propagation in the subsurface of the moon is affected by attenuation, transmission, scattering and so on. The echo of the sub-surface sky point is often very weak. Under the influence of lunar surface roughness, craters and other lunar topography, the strong clutter from the non-celestial surface often inundates the weak subsurface echoes, which becomes the biggest obstacle to the exploration of the subsurface structure of the moon. So far there is little research on how to extract weak subsurface echoes from radar detector echoes with strong background clutter. In order to detect the subsurface structure of the moon effectively, based on the coherent and non-coherent characteristics of the lunar subsurface celestial point echo and the surface non-celestial point echo (clutter), it is proposed that under the condition that the subsurface topography of the moon does not change much, The method of cumulatively averaging is used to suppress the surface non-celestial echo so as to identify the sub-surface echo. The validity and feasibility of the method are verified by numerical simulation of lunar sea and lunar land surface radar echo, and the effect of cumulative average number on the result of subsurface echo extraction is discussed. The method described in this paper can also be applied to the subsurface structure of other alien spheres, such as Mars, as well as to the exploration of liquid water.
【学位授予单位】：复旦大学
【学位级别】：硕士
【学位授予年份】：2010
【分类号】：P184.5
【参考文献】
相关期刊论文 前2条
1 法文哲;金亚秋;;雷达探测仪对月球次表层结构的探测模拟方法[J];中国科学:地球科学;2010年04期
2 ;SAR imaging simulation for an inhomogeneous undulated lunar surface based on triangulated irregular network[J];Science in China(Series F:Information Sciences);2009年04期
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