联合GNSS和卫星测高估计低阶重力场变化与大尺度质量迁移

Low degree gravitational coeffcients are larer than other gravity field model coefficients in the magnitude of order, particularly degree 1 and degree 2, while the degree 1 is directly related to geocenter motion and degree 2 is connected with polar motion and length-of-day variations. Meanwhile the low degree gravitational coefficients are closely related to mass redistribution within the Earth system. Therefore precise estimates of low degree gravitational coefficients greatly contributes to determine gravity field model and understand geocenter motion, earth rotation, fliud mass transport and coupling, and climate change. Currently the low degree gravitational coefficients were tranditionally measured by satellite laser ranging (SLR) or satellite gravimetry (e.g., GRACE). However, the SLR still has some problems and GRACE is not senstive to degree 1 and degree 2/order 0. In this project, the GNSS models and algorithms are further improved, which are used to re-process global GNSS data. The low degree gravitational coefficients are estimated by GNSS re-processed solutions and combining with satellite altimetry-derived ocean bottom pressure variations. The variations and mechanisms of low degree gravitational coefficients are investigated at seasonal, inter-annual, acceleration and long-term scales as well as understnainding the geocenter motion and earth rotation. Moreover, the characteristics of global large-scale mass transport are studied as well as their geophysical implications, e.g.,climate change reponses of glacier isostatic adjustment (GIA), ice/glacier melting, drought and EI-Nino events.

低阶地球重力场系数量级相对于其它系数大，特别是一阶项和二阶项，且一阶项体现地心运动，二阶项直接与地球自转运动相关，同时低阶重力场系数与地球内部物质流动密切相关。因此精确估计低阶重力场系数对确定重力场模型和理解地心运动、地球自转、各种流体质量耦合和气候变化等具有重要意义。目前国际上主要利用卫星激光测距或卫星重力测量(如GRACE)得到，然而激光测距仍存在诸多问题，而GRACE对一阶项和二阶项C20不敏感。本项目将进一步精化GNSS模型和算法，再处理全球连续GNSS观测资料得到高精度的综合解。利用再处理的GNSS质量位移以及联合卫星测高得到的海底气压资料分别估计低阶地球重力场系数，分析低阶地球重力场系数季节性、年季、加速度和长期变化及其机理，并理解地心运动和地球自转，以及获取全球大尺度地表流体质量重新分布特征和地球物理暗含, 包括冰期后回弹、冰雪融化、干旱和厄尼诺等气候变化响应。

低阶地球重力场系与地心运动和地球自转运动等息息相关，同时反应地球内部物质迁移。因此精确估计低阶重力场系数对确定重力场模型和理解地心运动、地球自转、各种流体质量耦合和气候变化等具有重要意义。目前国际上主要利用卫星激光测距或卫星重力测量(如GRACE)得到，然而激光测距仍存在诸多问题，而GRACE 对一阶项和二阶项C20 不敏感。本项目进一步精化GNSS 模型和算法，再处理全球连续GNSS 观测资料得到高精度的综合解，利用再处理的GNSS 质量位移以及联合卫星测高得到的海底气压资料分别估计低阶重力场系数，并分析低阶重力场变化与大尺度质量迁移特征。项目执行四年，获得以下创新性成果：（1）精化和提高了GNSS导航定位误差模型，如GNSS多路径延迟和电离层高阶项改正，获得了高精度GNSS导航定位结果；（2）联合全球连续GPS坐标时间序列和卫星测高得到的海底压力资料估计了60阶月变重力场系数，与美国Texas大学空间研究中心(CSR)GRACE解相当；（3）利用区域密集连续的GPS观测资料获取了美国西南部区域水储存总量变化，并获得2012年严重干旱变化特征；（4）利用正演模型扣除了海陆泄露影响，较好地准确估计了格林兰岛冰川融化；（5）在国际上首次利用GPS台站垂直位移时间序列反演了密西西比河流域的水储量变化和蒸散量变化，并发现密西西比河流域ET变化主要受地表温度控制等。本项目发表SCI论文40余篇，会议论文30余篇。培养硕士研究生8名，博士研究生7名，博士后1名。获软件著作权2项和实用新型专利1项，以及获上海市科技进步二等奖(12/2014)和中国卫星导航定位科技进步一等奖一项(09/2017)等。