Time-variable gravity and mass redistribution from synergistic use of GRACE-FO and Chinese gravity satellites

目前，中国正在准备一对重力卫星（天琴2号），这将实现一个非常类似于GRACE-FO的领导者-追随者概念。如果获得批准，当GRACE-FO仍在轨道上运行时，天琴2号很可能进入其操作阶段。在此，我们提出(1)在仪器处理层面（中国研究组）和后处理层面（德国研究组）改进重力建模技术；(2)通过模拟来优化天琴2号轨道，假设它可以与GRACE-FO一起飞行；(3)在空间分辨率起关键作用的两个重要应用中改进GRACE-FO的质量再分配估计。并评估如果与GRACE-FO平行飞行，调整天琴2号轨道的潜在效益。对于(3)，我们将解决东海的区域海平面预算，这是一个边缘海洋区域，海平面上升高于平均水平，可能带来巨大的生态，经济和政治后果，并且假设河流沉积变化对该区域的贡献很大。第二个地区是华北平原，这是中国人口最密集和农业最重要的地区之一，在那里观测到的大信号被认为是地下水抽取造成的。

Currently, China prepares for a pair of gravity satellites (TianQin-2) which would realize a leader-follower concept very similar to GRACE-FO. If approved, TianQin-2 may very well reach its operational phase when GRACE-FO is still in orbit. Here we propose (1) to improve gravity modelling techniqes both at instrument processing level (Chinese group) and in the postprocessing (German group), (2) to optimize the TianQin-2 orbit through simulations, assuming it can be flown in conjunction with GRACE-FO, and (3) to improve mass redistribution estimates from GRACE-FO in two important applications where spatial resolution plays a key role, and assess the potential benefit of adjusting the TianQin-2 orbit if flown in parallel with GRACE-FO. For (3) we will address the regional sea level budget in the East China Sea, a marginal ocean region where sea level rise is above-average with potentiallytremendous ecological, economical and political consequences, and where a large contributions from changes in river sedimentation is hypothesized. The second region is the North China Plain, one of China’s most densely populated and agricultarally important areas and where large signals have been observed and ascribed to groundwater withdrawals.