1. Department of Geodesy and Geomatics Engineering, School of Civil and Transportation, Engineering, Guangdong University of Technology , Guangzhou 510006 , China
2. Department of Geography, University College London , Gower Street, London WC1E 6BT , UK
3. Cross Research Institute of Ocean Engineering Safety and Sustainable Development, Guangdong University of Technology , Guangzhou 510006 , China
4. National Precise Gravity Measurement Facility, Huazhong University of Science and Technology , Wuhan 430074 , P.R.China
5. State Key Laboratory of Geodesy and Earth's Dynamics, Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences , Wuhan 430077 , China