GRACE重力计划在揭示地球系统质量重新分布中的应用

Mass Redistribution to be Revealed by GRACE Project

2002年3月成功发射的美德合作卫星重力计划GRACE(Gravity Recovery And ClimateExperiment),即将提供空间分辨率约为200 km而时间分辨率为1个月的时变地球重力场模型序列。GRACE计划的星座由两颗相距约220 km,高度保持为300-500 km、倾角保持约90°的近极轨卫星组成。由于采用星载GPS和非保守力加速度计等高精度定轨技术,以及高精度的星一星跟踪数据反演地球重力场,在几百公里和更大空间尺度上, GRACE重力场的精度大大超过此前的卫星重力计划。根据GRACE时变重力场反演的地球系统质量重新分布,将对固体地球物理、海洋物理、气候学以及大地测量等应用有重要的意义。虽然其设计寿命只有5 yr,但研究表明GRACE的结果可用于研究北极冰长期时间尺度的变化,并进而研究极冰融化对全球气候变化,特别是对海平面长期变化的影响。在季节性时间尺度上,利用GRACE重力场反演的质量重新分布足以揭示平均小于1 cm的地表水变化,或小于1 mbar。的海底压强变化。除了巨大的社会效益和经济效益外,这些变化对了解地球系统的物质循环(主要是水循环)和能量循环有非常重要的意义。介绍GRACE重力场揭示的地球系统质量重新分布,为理解其地球物理应用提供必需的准备;同时针对我国大陆和沿海地区的地球物理应用提出初步的设想。

The successful launch of the GRACE twin satellites in March, 2002 for gravity and climate study, which is a US and Germany co-sponsered project, will deliver time-varying gravity models with unprecedented precision. The two identical satellites are about 220 km apart on a nearly polar orbit with an altitude of 300~500 km. On aboard GPS data and accelorometer mearuments are used to precisely determine the orbits, and range change rate measurements between the twin satellites are used to recover gravity to much higher precision than before at spatial scales of a few hundred km and larger. The mass redistribution data derived from the GRACE time-varying gravity models will have profound impacts on various geophysical research topics. Despite of its designed 5-year lifetime, simulation studies have shown that the GRACE gravity will provide important information on secular change of ice sheets, and global mean sea level change. At seasonal time scales, GRACE gravity is capable to detect land water change less than 1 cm or change in oceanic bottom pressure less than 1 mbar. Besides social and economical importance, knowledge in mass redistribution helps us understand both water mass and energy transfer. The purpose of this paper is to provide necessary background for understanding various prosesses of mass redistribution, and to propose application studies focusing on China and neighboring oceans.