Abstract
In this paper, the detection of the lunar surface soil permittivity with megahertz electromagnetic (EM) waves by spaceborne radar is studied based on the EM scattering theory, the Boltzmann–Shukla equations, and the improved scattering matrix method (ISMM). The reflection characteristics of the lunar surface soil subject to megahertz waves are analyzed through the EM scattering theory and expressed by the lunar surface soil permittivity. Then, the lunar ionosphere is assumed to be composed of dusty plasma, and its EM characteristics are described with the Boltzmann–Shukla equations. Finally, the transmission and reflection characteristics of the propagation of EM waves in the lunar ionosphere are numerically calculated with ISMM. Thus, the complex permittivity of lunar surface soil is obtained. In addition, the effects of detection environment situations, such as the lunar illumination intensity, characteristics of the lunar dust and dust charging process in the lunar ionosphere, on the amplitude and phase of EM waves are also investigated in this study. The simulation results show that an EM wave at a high frequency induces a strong effective wave with a stable phase shift and a significantly small interferential wave. Moreover, the lunar illumination is more effective under EM waves in low frequency bands; the characteristics of the lunar dust have a notable influence on the transmission and absorption coefficients of the effective waves. These conclusions help in real applications involving the detection of the lunar surface soil permittivity by spaceborne radar in various lunar environments.
Highlights
The Moon is the only satellite of the Earth, and the study of the Moon has great significance
In the Apollo project, the lunar ionosphere was detected to be composed of plasma with much active dust that differs from normal plasma in its charging properties [22]
Based on the EM scattering theory, Boltzmann–Shukla equations, and the improved scattering matrix method, the complex permittivity from both the amplitude and phase shift of the reflection wave is investigated in this paper
Summary
The Moon is the only satellite of the Earth, and the study of the Moon has great significance. There is a pressing need to study the propagation characteristics of electromagnetic (EM) waves in the dusty plasma on the lunar surface. The propagation properties of the EM in the lunar dusty plasma, which comes from the lunar ionosphere and could reflect the detection signal, resulting in the interruption of communication, have rarely been studied, to the best of our knowledge. An algorithm for calculating the dielectric constant of lunar surface soil is proposed, and the influence of interference signals is considered in this method. A satellite can capture two kinds of reflected waves: wave carrying information about the lunar surface soil permittivity, known as effective wave, and wave totally caused by the reflection of the ionosphere, known as interferential wave. The total electron content (TEC) of the three electron distribution profiles is 2.59 × 1013 m−2, 3.31 × 1013 m−2, and 1.70 × 1013 m−2, respectively
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