1. College of Civil Engineering, Xiangtan University, Xiangtan 411105, China
2. College of Geodesy and Geomatics, Shandong University of Science and Technology, Qingdao 266590, China
3. School of Geospatial Engineering and Science, Sun Yat-sen University, Zhuhai 519082, China
4. Key Laboratory of Comprehensive Observation of Polar Environment, Ministry of Education, Sun Yat-sen University, Zhuhai 519082, China
5. School of Geosciences and Info-Physics, Central South University, Changsha 410083, China