1. Collaborative Innovation Center of Geospatial Technology/Key Laboratory of Geospace Environment and Geodesy, School of Geodesy and Geomatics, Wuhan University, 430079Wuhan, China
2. Helmholtz Centre Potsdam, GFZ German Research Centre for Geosciences, 14473Potsdam, Germany
3. National Oceanic and Atmospheric Administration, Silver Spring, MD 20910, USA