基于质量迁移指纹和GRACE数据解算地心运动及地球动力学扁率时变

Geocenter motion is the key to establish and maintain the origin of the terrestrial reference frames and J2 is one of the basic constant of the Earth’s reference ellipsoid. Meanwhile, they are closely related to the low degree gravity field coefficients can are therefore indispensable elements to complement the time-variable gravity field models and to estimate mass transportation in the Earth system. However, the current accuracy is not sufficient and still need to be improved. In this project, we first estimate the fingerprints of regional mass redistribution through the sea level equation. These fingerprints are then combined with Gravity Recovery And Climate Experiment (GRACE) time-variable gravity field models to reveal large-scale mass transportation in the Earth system in order to determine geocenter motion and J2 time variations due to mass redistribution. In this research, we identify reasonable scheme of separating mass redistribution regions and modes and determine the optimal parameter setting through an end-to-end simulation. We then compare our results with alternative solutions obtained with forward modeling approach in an attempt to investigate the driving mechanisms. Such a method has the advantages of using uniformly distributed, continuously observed GRACE measurements, and do not directly dependent on geophysical models. Therefore, the solutions are reliable as they are free from the network effect and models with unknown uncertainties. These results are not only invaluable for complementing current GRACE gravity field model solutions , but also meaningful for the improve of GRACE-Follow On and the Chinese gravimetry mission products in the near future. More importantly, they are also important for various application such as establishing a stable reference frame, monitoring mass redistribution and sea level rise, understanding the ongoing climate change.

地心运动是维护地球参考框架原点的关键；地球动力学扁率（J2）则是地球椭球的基本常数之一，二者对于建立完整的地球重力场模型和估计质量迁移不可或缺，但目前精度均不满足需求。本项目利用海平面方程解算局部质量迁移所激发的特有重力场变化（指纹），结合GRACE实测重力场变化反演地球系统大规模质量迁移，同时求解由质量迁移导致的地心运动和J2时变。着重讨论指纹数据集的合理构建及利用模拟研究确定最佳参数设置。该方法的优势在于使用均匀分布、观测连续的GRACE数据，其结果不受非质量迁移因素及站网偏差影响，且不直接依赖地球物理模型，可以提供可靠的地心运动和J2时变时间序列。通过比较分析二者多尺度变化特征，并结合多种地球物理模型正演结果，揭示其物理驱动机制。产品可改善GRACE及其后续卫星的重力场场模型，对于参考框架建立，海平面和质量迁移监测以及理解气候变化具有重要意义。

地心运动及地球动力学扁率时变是大地测量学领域的支柱问题，前者是维护地球参考框架原点的关键，而后者是地球椭球的基本常数之一，二者对于解算完整的地球重力场模型以及估算地表质量迁移不可或缺，但目前精度均不满足需求。本项目通过深入探讨地表质量迁移特征，合理划分质量迁移区块，通过解算海平面方程得到质量迁移区块经历区块内部均一分布的单位质量变化时所激发的特有重力场变化（指纹），建立指纹数据库；结合GRACE实测重力场变化反演地球系统大规模质量迁移，同时解算由此所导致的地心运动及地球动力学扁率时变，并于其他方法及地球物理模型预测结果进行对比分析；最后，利用指纹数据集和GRACE数据分离出固体地球信号，解算半经验的全球冰川均衡调整模型。该研究对于改善GRACE及其后续卫星的重力场模型，维护地球参考框架，估计地表大规模质量迁移等具有重要意义。