新53阶次月球重力场及其精细结构

A new lunar gravity field model at degree and order 53 and its detailed structures

月球重力场是了解月球内部结构的重要信息之一.日本SELENE卫星首次获得月球背面卫星轨道的直接探测数据并建立了更高精度的全月球重力场模型.本文根据日本公布的采样间隔为60s、轨道高度为100km的SELENE卫星观测资料并利用作者移植的GEODYN-II微机版本软件求解出新53阶次月球球谐场模型LG-53.经过测试表明移植后的微机版本比原始工作站版本的计算效率提高了5到10倍.理论上表明60s采样间隔、100km高度的轨道数据能够计算出60阶次的月球球谐系数模型,但是作者在实际计算过程中发现:在接近理论阶次(60阶次)的一系列模型中出现了平行于经线的高频噪声,且模型越接近理论阶次其噪声越高.因此本文将53阶次月球球谐系数模型LG-53作为最后的解算结果并建立各种月球重力异常场,并将其与美国GLGM-2(70阶次)模型和利用嫦娥1号数据解算出的CEGM-01(50阶次)模型对比,发现新53阶次重力场模型LG-53在高纬度和月球背面都显示出了更高分辨率的异常特征;与美国LP165P(165阶次)模型对比发现LG-53所建立的自由空气重力异常在月球背面不存在LP165P中所出现的高频噪声.与日本90阶次SGM90d模型对比后发现新模型的精度较日本模型还有所差距.主要是由于两者参与计算的数据采样率不同所致.53阶次的模型LG-53能够反映100km尺度的重力异常,而日本90阶次模型则可以反映60km尺度的异常.利用新53阶次模型计算的自由空气重力异常图并结合月球地形图探讨了四种类型的Mascon重力异常特征及其地形特征.

Lunar gravity field is one of the most essential information to understand the interior structure of the Moon. The Japanese satellite, SELENE, was the first to directly detect the orbital data on lunar farside, and then the gravity model of the whole moon in higher accuracy was established using the data set. Together with the data set from SELENE observed at altitude of 100 kilometers with 60 seconds of sampling interval, GEODYN-II software transplanted onto a microcomputer system by the author is used for solving a new spherical harmonic coefficient model of the moon at degree and order 53, LG-53 model. The test of the transplanted codes on a microcomputer system indicates that it will provide 5 to 10 times higher efficiency than the original codes run on a workstation system. The tracking data at altitude of 100 kilometers with 60 seconds of sampling interval is proved in principal to be capable of calculating sphericalharmonic coefficient model of the moon at degree and order 60. Actually, in calculation process, it is found out that when the degree of a model is closer to 60, there is more noise appeared parallel along the longitude in the model. In this paper, therefore, the spherical harmonic coefficient model of the moon at degree and order 53, LG-53 is finally chosen to be the best one. Various lunar gravity anomalies are calculated based on this new model. Compared with the maps of lunar gravity anomalies from GLGM-2 （70th） by US and CEGM-01 （50th） by CE-1, the new ones at degree and order 53 present more accurate gravity anomalies in high latitude areas and lunar farside. Comparing with LP165P（165th） by US, the high frequency noise on the lunar {arside in that model does not exist in the map of free air gravity anomalies of LG-53. Another comparison with Japanese lunar gravity model at degree and order 90, SGM90, implies that there is still space for improvement in accuracy for the new model. The reason resides mainly in the different sampling intervals of the two models. After all, the 53r~ degree lunar gravity model can represent the anomalies more than 100 kilometers long, and the 90th degree model from Japan can represent the anomalies more than 60 kilometers long. The features in gravity anomalies and lunar topography in four categories of mascons are discussed finally with the maps o{ lunar free gravity anomalies for LG-53 model and topography of the moon.