Study of Chang’E-2 Microwave Radiometer Data in the Lunar Polar Region

Fan Yang,Yi Xu,Kwing Lam Chan,Yong Li,Xiaoping Zhang,Guoping Hu

doi:10.1155/2019/3940837

Fan Yang, Yi Xu + Show 4 more

Open Access

https://doi.org/10.1155/2019/3940837

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Abstract

The Chang’E-2 (CE-2) four-channel microwave radiometer (MRM) data with frequencies of 3 GHz, 7.8 GHz, 19.35 GHz, and 37 GHz have been used to investigate the properties of lunar surface such as regolith thickness, dielectric constant, and titanium abundance within a depth of several meters in middle and low latitudes. The purpose of this work is to take a close look at MRM data in the polar regions of the Moon and analyze the characteristics of the brightness temperature (TB) in permanently shadowed regions (PSRs), especially where evidence of water ice has been found. First, the comparisons of brightness temperature values in the polar region and in low latitudes show that (1) the periodic diurnal (day/night) variation of TB becomes weak in high latitudes since topography plays a dominant role in determining TB in polar region and (2) seasonal effects are more recognizable in polar region than in low latitudes due to the weak illumination condition. Second, even without direct sun illumination, significant seasonal variations of TBs are observed in PSRs, probably caused by the scattering flux from neighboring topography. TB Ratio (TBR) between channel 1 and channel 4, which indicates the differences of TB at different depths of lunar regolith, is higher and shows stronger seasonal variation in PSR than regions with direct illumination. Third, overall the distribution of high TBR values is in consistence with the water ice distributions obtained by the Moon Mineralogy Mapper instrument, the LAMP UV spectra, and the Lunar Prospector Neutron Spectrometer. The proportion of the summation over area with water ice proof in the regions of interest is 0.89 and 0.56 in south pole and north pole, respectively. The causes of the correlation of high TBR between different microwave frequencies and stability of water ice deposits still require further investigation, but MRM data shows unique characteristic in PSRs and could provide important information about the upper few meters of lunar regolith.

Highlights

Since Selene, Chang’E, Chandrayaan-1, and Lunar Reconnaissance Orbiter have fulfilled their missions successfully, more and more questions about the Moon appear
With the Miniature Radio Frequency (Mini-RF) radar data, Spudis discovered a different class of polar crater that exhibits high circular polarization ratio (CPR) which may associate with the presence of water ice [6]
The comparisons of the TB variations in different latitudes show that the periodic diurnal variation of TB is dominant in the low latitude and becomes weak in the polar region

Summary

Introduction

Since Selene, Chang’E, Chandrayaan-1, and Lunar Reconnaissance Orbiter have fulfilled their missions successfully, more and more questions about the Moon appear. Li found the direct evidence of the surface exposed water ice in the lunar polar region with the Moon Mineralogy Mapper (M3) instrument on the Chandrayaan-1 spacecraft [12]. In Apollo era, a series of microwave ground-based observations of the Moon was made to obtain the physical parameters of the lunar surface by simulating the brightness temperature (TB) with theoretical models [16,17,18,19,20,21,22]. The purpose of this work is to take a close look at MRM data in the polar regions of the Moon and analyze the characteristics of the TB in permanently shadowed regions, especially where plausible evidence of water ice has been found

Chang’E TB Data

Data Comparisons and Analysis

Conclusions