Application of Mathematical Morphological Filtering to Improve the Resolution of Chang'e-3 Lunar Penetrating Radar Data

Jianmin Zhang,Zhaofa Zeng,Qi Lu,Ling Zhang,Kun Wang

doi:10.3390/rs11050524

Abstract

As one of the important scientific instruments of lunar exploration, the Lunar Penetrating Radar (LPR) onboard China’s Chang'E-3 (CE-3) provides a unique opportunity to image the lunar subsurface structure. Due to the low-frequency and high-frequency noises of the data, only a few geological structures are visible. In order to better improve the resolution of the data, band-pass filtering and empirical mode decomposition filtering (EMD) methods are usually used, but in this paper, we present a mathematical morphological filtering (MMF) method to reduce the noise. The MMF method uses two structural elements with different scales to extract certain scale-range information from the original signal, at the same time, the noise beyond the scale range of the two different structural elements is suppressed. The application on synthetic signals demonstrates that the morphological filtering method has a better performance in noise suppression compared with band-pass filtering and EMD methods. Then, we apply band-pass filtering, EMD, and MMF methods to the LPR data, and the MMF method also achieves a better result. Furthermore, according to the result by MMF method, three stratigraphic zones are revealed along the rover's route.

Highlights

Lunar Penetrating Radar (LPR) is one of the main payloads mounted on the “Yutu” rover of China’s Chang’E-3 (CE-3) spacecraft [1,2]
In order to improve the quality of radar image and obtain better information of the lunar subsurface structure, many filtering methods have been applied to the LPR data, such as deconvolution processes [12], background removal [10,13], bi-dimensional empirical mode decomposition filtering [2], amplitude compensation [8,10], band-pass filtering [5,11] etc
In order to show the superiority of morphological filtering in suppressing both high frequency and low frequency information, we used band-pass filtering and empirical mode decomposition filtering (EMD) methods to process signal 3, respectively

Summary

Introduction

Lunar Penetrating Radar (LPR) is one of the main payloads mounted on the “Yutu” rover of China’s Chang’E-3 (CE-3) spacecraft [1,2]. The processing result of the LPR data from N201 to N203 indicates the thickness of the regolith and the locations and physical parameters of some rocks [2] These results were obtained based on the extraction and analysis of useful echo signals, which is a complicated procedure because the useful signals are often masked by noise. In order to improve the quality of radar image and obtain better information of the lunar subsurface structure, many filtering methods have been applied to the LPR data, such as deconvolution processes [12], background removal [10,13], bi-dimensional empirical mode decomposition filtering [2], amplitude compensation [8,10], band-pass filtering [5,11] etc. The morphological filtering method is applied to the processing of the CE-3’s 500 MHz data, and achieved good results, namely the lunar subsurface structure was clearly imaged

Basic Theory

Selection of Structural Elements

Synthetic signal test

Discussion

Conclusions