Atmospheric, oceanic and hydrological polar motion excitation mechanisms based on a combination of geometric and gravimetric space observations

The goal of our study is to determine accurate time series of geophysical Earth rotation excitations to learn more about global dynamic processes in the Earth system. For this purpose, we developed an adjustment model which allows to combine precise observations from space geodetic observation systems, such as Satellite Laser Ranging (SLR), Global Navigation Satellite Systems (GNSS), Very Long Baseline Interferometry (VLBI), Doppler Orbit determination and Radiopositioning Integrated on Satellite (DORIS), satellite altimetry and satellite gravimetry in order to separate geophysical excitation mechanisms of Earth rotation. Three polar motion time series are applied to derive the polar motion excitation functions (integral effect). Furthermore we use five time variable gravity field solutions from Gravity Recovery and Climate Experiment (GRACE) to determine not only the integral mass effect but also the oceanic and hydrological mass effects by applying suitable filter techniques and a land–ocean mask. For comparison the integral mass effect is also derived from degree 2 potential coefficients that are estimated from SLR observations. The oceanic mass effect is also determined from sea level anomalies observed by satellite altimetry by reducing the steric sea level anomalies derived from temperature and salinity fields of the oceans. Due to the combination of all geodetic estimated excitations the weaknesses of the individual processing strategies can be reduced and the technique-specific strengths can be accounted for. The formal errors of the adjusted geodetic solutions are smaller than the RMS differences of the geophysical model solutions. The improved excitation time series can be used to improve the geophysical modeling.本研究的核心目标为获取高精度的地球自转的地球物理激发（geophysical Earth rotation excitations）时间序列，以深入探究地球系统内的全球动力过程。为此，本研究构建了一套平差模型，可融合各类空间大地测量观测系统的高精度观测数据，包括卫星激光测距（Satellite Laser Ranging, SLR）、全球导航卫星系统（Global Navigation Satellite Systems, GNSS）、甚长基线干涉测量（Very Long Baseline Interferometry, VLBI）、卫星多普勒定轨与无线电定位集成系统（Doppler Orbit determination and Radiopositioning Integrated on Satellite, DORIS）、卫星测高以及卫星重力测量，以此分离地球自转的地球物理激发机制。本研究利用3组极移时间序列，推导得到极移激发函数（polar motion excitation functions，对应积分效应）。此外，本研究借助重力恢复与气候实验（Gravity Recovery and Climate Experiment, GRACE）提供的5组时变重力场解，通过应用合适的滤波技术与陆海掩膜，不仅可确定积分质量效应，还可分离海洋与水文质量效应。为开展对比分析，本研究还基于卫星激光测距（SLR）观测得到的二阶位系数，推导得到积分质量效应。海洋质量效应还可通过卫星测高观测得到的海平面异常，扣除由海洋温度与盐度场推导得到的比容海平面异常后计算得到。通过融合所有大地测量估算得到的激发序列，可弱化单一处理策略的固有缺陷，同时兼顾各观测技术的专属优势。经平差得到的大地测量解的形式误差，小于地球物理模型解的均方根（Root Mean Square, RMS）差异。本研究得到的优化后激发时间序列，可用于改进地球物理建模工作。