Prospect for Measuring Lunar Tidal Deformation and Displacement Love Numbers With Earth-Based Radar

Abstract

Lunar tidal deformation (LTD), characterized by the vertical (𝒉 𝟐 ) and horizontal (𝒍 𝟐 ) displacement Love numbers, is a key to deciphering the interior structure of the Moon. However, the small deformation amplitude of only up to 10 cm makes their measurements very challenging. In this paper, we propose a novel method named Earth-based repeat-pass SAR interferometry (EBRP-InSAR) to measure the LTD and displacement Love numbers. We analyzed the potential and performance of EBRP-InSAR in detail based on LTD model and existing planetary radar capabilities. The error budget and simulation results show that the relative measurement accuracy of LTD could be better than 2 mm. Furthermore, compared with Lunar Laser Ranging (LLR) and Lunar Orbiter Laser Altimeter (LOLA), the two-pass EBRP-InSAR can not only directly estimate 𝒉 𝟐 but also 𝒍 𝟐 with accuracies better than 𝟏𝟎 −𝟑 and 𝟏𝟎 −𝟒 , respectively, which is comparable that of LLR and LOLA methods. In addition, through long-term time-series observations, it will be possible to assess the spatial inhomogeneity of LTD response to the forcing potential in the near side with time-series EBRP-InSAR. After spatial smoothing, a space variation as small as on the order of 𝟏𝟎 −𝟒 and 𝟏𝟎 −𝟓 in 𝒉 𝟐 and 𝒍 𝟐 , respectively, can be distinguished on the lunar near side. As another measurement technology independent of LLR and LOLA, the EBRP-InSAR is expected to explain the difference between the observations from LLR and LOLA and the modeled lunar interior structure, and firstly estimate the lunar horizontal displacement Love number.