模拟分析低低跟踪模式重力卫星反演地球重力场的精度

本文利用卫星重力反演与模拟软件ANGELS系统(ANalyst of Gravity Estimation with Low-orbit Satellites)对低低跟踪模式的重力卫星的关键载荷精度指标进行了深入分析.模拟结果表明:(1)对短弧长积分法而言,在低低跟踪模式的关键载荷精度指标中,重力场反演精度对星间距离变率精度最为敏感;(2)通过对目前在轨运行GRACE的载荷指标进行分析,发现轨道数据的误差主要影响重力场的低阶部分(约小于25阶),较高阶次部分(约大于26阶)主要受星间距离变率的误差限制;(3)如果下一代低低跟踪模式的重力卫星的目标之一是把重力异常反演精度较GRACE提高约10倍,则在保持轨道高度和GRACE相同的前提下,轨道、星间距离变率和星载加速度计等关键载荷指标需要达到的最低精度分别约为2cm、10nm·s-1和3.0×10-10 m·s-2;(4)轨道精度和混频误差将是影响下一代低低跟踪模式重力卫星重力场恢复能力进一步提高的主要制约因素,距离变率精度和加速度计精度存在盈余.

Analysis of the gravity field recovery accuracy from the low-low satellite-to-satellite tracking mission

Gravity Recovery And Climate Experiment mission (GRACE), which was launched in 2002, has provided a viable way to investigate the mass variations happened on the Earth surface. GRACE, however, will terminate in the near future. Thus many research groups begun to propose the next generation of low-low satellite to satellite tracking mission, such as the GRACE Follow-On mission from the National Aeronautics and Space Administration and the German Aerospace Center, the Earth System Mass Transport Mission (e.motion) from the European Space Agency, and China's future satellite gravity mission. In this paper, we focus on the simulation study of China's future satellite gravity mission which is proposed by Chinese Academy of Sciences, cooperating with Huazhong University of Science and Technology, Aerospace Dongfanghong Satellite Company and so on. One of the goals of China's future satellite mission is to improve the accuracy of the gravity field model by a factor of 10, compared with that of GRACE. To that end, the minimum requirements of the key payloads are of great importance to be clarified. Here we try to answer this research question by numerical simulations. Several methodologies have been widely used to process the data collected by GRACE mission, such as variation equation approach, acceleration approach, energy integral approach and short arc approach. Because of small accumulative numerical integration error and stronger flexibility to deal with data gaps, short arc approach is selected and applied to do the analysis in this work. Based on short arc approach, a software named ANalyst of Gravity Estimation with Low-orbit Satellites (ANGELS) was developed by us. In order to validate the output produced by ANGELS, a new series of monthly gravity field model named IGG-CAS 01, which was truncated up to degree/order 60, was recovered using ANGELS. By comparing the mass variation trends at both Greenland and China from 2004 to 2010 computed from IGG-CAS 01 and CSR RL05, we find the correlation number are around 0.9, which confirms that IGG-CAS 01 is comparable with CSR RL05. Finally, ANGELS was used to analyze the key payloads of the low-low satellite-to-satellite tracking mission in this study. The numerical results show: (1) the precision of range rate, as for short arc approach, is the most sensitive impact factor compared with other payloads of the low-low satellite-to-satellite tracking mission; (2) by analyzing the error budget of the ongoing GRACE mission in terms of geoid height per degree, the error in orbit position is the major error source for degrees which are smaller than ~25, while the error of range rate dominates for degrees which are larger than ~26; (3) aiming to improve the gravity field model recovery accuracy by a factor of 10, the minimum requirements of the accuracies of orbit position, range rate and acceleration are 2 cm, 10 nm·s^-1 and 3.0×10^-10 m·s^-2, respectively; (4) the accuracy of orbit position and the error of de-aliasing model will be the two major error sources of next low-low satellite-to-satellite tracking gravity satellite mission.