1. Department of Earth Sciences, University of Hong Kong, Pokfulam Road, Hong Kong
2. Department of Geoscience, University of Calgary, Calgary, Alberta T2N 1N4, Canada
3. Geodata Division, Lantmäteriet, Lantmäterigatan 2C, 80182Gävle, Sweden
4. State Key Laboratory of Geodesy and Earth’s Dynamics, Institute of Geodesy and Geophysics, Chinese Academy of Sciences, Wuhan 430077, China