μm级GEO/GNSS-LEO高低卫星跟踪模式确定地表浅层物质迁移的关键技术研究

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.

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。

项目基于欧空局GETRIS未来重力计划的理念，研究了微米级测距的GEO-LEO星间链路和GNSS-LEO低轨卫星精密定轨方法，完成了一整套基于高精度测距的低轨卫星精密定轨算法和软件系统；开展了高-低跟踪（GEO-LEO）、中-低跟踪（GNSS-LEO）、低-低跟踪（类GRACE模式）及基线组合（GEO/GNSS-LEO+GRACE）模式的μm级测距确定地球时变重力场关键技术研究，研究了GEO、GNSS、LEO星座的最优几何结构，分析了GEO-LEO、GNSS-LEO和GEO-GNSS-LEO三种组合模式确定时变重力场的能力，探究了不同星座高/中-低组合测距和μm级径向、沿轨基线不同组合模式削弱时变重力场信号中混频效应的能力，形成了一整套基于μm级高精度长距离测距确定地球时变重力场的理论算法；突破利用卫星重力数据反演地表浅层物质迁移变化的关键技术，提出了联合机器学习、统计分解和时间序列分解重构/预测全球陆地水储量变化的方法，重构/预测了1992年至2019年的全球陆地水储量变化数据集（0.5°×0.5°），自主研发了一整套全自动化陆地水储量变化预测软件包；研究了提高浅层地表物质迁移时空探测能力的方法，采用小波-逐步回归方法，联合GRACE、Swarm、GRACE-FO卫星数据、气候驱动方法探测及预测区域内点位长时期的地下水储量变化；研究了区域和局部地区浅层物质迁移的关键技术及应用，利用Swarm数据填补GRACE与GRACE-FO任务间的数据缺失，构建极地地区连续的长期冰盖质量变化时间序列，探测亚马逊流域干旱事件；融合水文、卫星重力等多源数据，建立我国东北地区地下水时空分布模型，分析金沙江流域GRACE信号中不同组成成分的时空物理特征，探究三峡大坝和人文活动对中国长江流域水储量变化的影响。本项目的研究成果可为下一代卫星重力计划提供指标设计依据，拓展当前卫星重力计划在大地测量学、地球物理学和水文学等相关学科中的应用领域，推动未来卫星重力计划在地球相关科学中的应用发展，具有重要的参考价值和现实意义。