1. Chinese Academy of Surveying and Mapping, Beijing 100036, China
2. Key Laboratory of Natural Resources Monitoring in Tropical and Subtropical Area of South China, Ministry of Natural Resources, Guangzhou 510670, China
3. State Key Laboratory of Information Engineering in Surveying, Mapping and Remote Sensing, Wuhan University, 129 Luoyu Road, Wuhan 430079, China
4. Department of Geosciences, University of Arkansas, Fayetteville, AR 72701, USA