Improved regional gravity fields on the Moon from Lunar Prospector tracking data by means of localized spherical harmonic functions

摘要

An approach to enhance regional gravity fields of the planets using the line-of-sight (LOS) Doppler range-rate measurements is presented. Instead of representing the gravity fields as nonlocalized spherical harmonic functions, I introduced a lumped harmonic representation for obtaining regionally concentrated orthogonal basis functions. Without any regularization or spectral power control, the gravity fields over the four spherical cap regions with the radius of 20° on the nearside of the Moon to degree and order 200 were estimated using all 8 months of the extended mission data from Lunar Prospector. The regional models are variations on the initial global gravity model LP100J. It was found that the regional estimates significantly improve the initial gravity model at all four regions of interest. My improved gravity models fit the LOS Doppler range-acceleration data better than any other global lunar gravity model, especially the data for when the satellite was at low altitude (40 km or less). In addition, a better cross correlation with the topography was obtained from the regional model. The regional enhancement of the correlation was prominent in degrees greater than 100 and in polar regions characterized by clusters of medium- or small-size craters that are presumably uncompensated.