本项目基于欧空局GETRIS未来重力计划的理念，研究μm级GEO/GNSS-LEO星间测距确定地球静态与时变重力场，反演地表浅层物质迁移的关键技术。项目拟开展高-中-低组合模式的μm级测距确定地球静态与时变重力场关键技术攻关，研究GEO、GNSS、LEO星座的最优几何结构，深入分析GEO/GNSS-LEO+GRACE组合模式确定时变重力场的能力，基于μm级径向、沿轨测距基线组合，重点解决经典时变重力场模型确定中难以消除的混频与时频效应，突破提高时变重力场时空分辨率的关键技术瓶颈，分离时变重力场中大气、海洋、水文、冰和固体地球物理的时变信号，描述地表浅层物质迁移的时空特性，形成一整套基于μm级高精度长距离测距确定地球时变重力场的理论算法和软件系统。本申请项目可望为未来卫星重力计划提供指标设计依据，推动未来卫星重力计划在地球相关科学中的应用发展，具有重要的理论价值和现实意义。

In this project the feasibility of gravity field determination with extreme high-low satellite-to satellite tracking, as intended as part of the ESA GETRIS (“Geodesy and Time Reference in Space”) mission concept, is investigated. For this purpose several geostationary satellites (GEOs) or GNSS are designed to be positioned around the Earth. A microwave system is applied to determine the distance between satellites in low Earth orbits (LEOs) and GEOs/GNSS with very high accuracy, from which the gravity field of the Earth can be estimated. This concept is simulated to retrieve the time-variable gravity field caused by temporal changes in continental hydrology. The GEO-LEO concept is very promising, since it possibly reduces some of the weaknesses of the LEO-LEO tracking concept and directly measures the radial component of the Earth’s gravity field. Due to the option of multi-satellite tracking, the time-variable gravity field can be observed within shorter time periods than with a single GRACE-like mission. This proposal intends to carry out key technology research on determining the static and time-variable earth gravity field with μm level range surveying between GEO/GNSS-LEO satellites. The optimal geometric structure of the constellation and the composite patterns of GEO, GNSS and LEO satellites are analyzed in-depth. The.influence of temporal aliasing on gravity solution is investigated based on μm level baseline of radial component and along tracking component. This project will try to break through the key technology bottleneck about the time-varying gravity space-time resolution. The atmosphere, oceans, hydrology, ice and solid geophysics time-varying signal in the time-varying gravity field should be separated. And the spatiotemporal characteristics of the mass distribution and mass transport in the Earth system will also be described. At last, one complete set of theoretical algorithms and software system for the determination of the time-varying earth gravity field through μm-level high accuracy long-distance range will be developed. This application is expected to provide the basis for designing the future satellite gravity missions, to promote the application and development of future satellite gravity missions in related earth sciences, which has important theoretical and practical significance.