为了更好地研究地球系统中的大尺度物质迁移，包括冰盖、海平面、固体地球、水汽圈之间的物质交换，本研究提出联合多种空间大地测量技术测量地心长期运动以及低阶时变重力场，研究跨度为1992年到2018年。具体研究内容包括：1. 从理论和观测两方面着手，联合卫星重力、雷达测高、GNSS、激光测距等多种技术手段研究地心的长期运动，尤其是源于当前质量变化的成分；2. 将得到的地心长期运动时间序列用于研究地球物理现象，包括GIA过程、ITRF的长期稳定性、以及冰盖质量平衡估计等；3. 利用改进的能量法联合GRACE、SWARM、测高、SLR等，研究地球重力场二阶球系数变化；4. 利用改进的能量法研究SWARM卫星对于精化低阶重力场（10阶左右）变化的贡献；5. 结合所得到的地心运动时间序列以及时变重力场时间序列，研究不同空间分辨率下的地球物质大尺度迁移。

Geocenter variation, defined as the motion of the center of mass (CM) of the Earth relative to its center of figure (CF), is arguably controversial in both its determination and the theoretical treatment at the secular component. There has been plausible evidence that the Earth’s recent accelerated ice melt, in particular, from the northern hemisphere ice reservoirs, has induced an observable geocenter Z-component motion which had affected International Terrestrial Reference Frame (ITRF) realizations. Both the secular geocenter component and the low-degree temporal gravity field coefficients, in particular, C20, have a significant impact on for Antarctic and Greenland ice-sheet mass balance estimates. However, at present the GRACE solution of C20 is relatively poor, and it has to be replaced by an independent solution using satellite laser ranging. ..We propose to study and quantify the present-day interactions between Earth’s ice reservoirs, sea-level, solid Earth, and hydrosphere, manifest in Earth’s geocenter and low-degree gravitational changes, which represents the largest scale mass transports within the Earth system, 1992–2018. Specifically, our scientific objectives include: (1) formulating a theoretically robust formalism and technically viable approach to use GRACE and SWARM data, SLR satellites, and satellite radar altimetry to estimate past, present and future present-day mass change (PMC) component of the geocenter motion, including its secular trends; (2) to study the constraint on degree 1 GIA processes, assessing the implication of a measurable geocenter secular motion on the stability of the ITRF, and its impact on GRACE ice-sheet mass balance estimates; (3) developing improved energy conservation approach for GRACE KBR (disturbance potential observables), and individual GNSS-tracked satellites (GRACE and SWARM) with accelerometers, SLR tracking and satellite altimetry data, to investigate improved C20 estimates in a joint solution for GRACE KBR monthly gravity solutions; (4) to implement the energy conservation method to use 3-satellite SWARM GNSS tracking and its formation-flying GNSS inter-satellite ranging data to estimate low-degree (~degree 10) temporal gravity field solutions; and (5) to conduct a study of large-scale mass transports associated with the Earth’s geocenter and temporal gravity field with varying spatial resolutions.