1. Library, Zhejiang University 1 , Hangzhou 310058, China
2. State Key Laboratory of Modern Optical Instrumentation 2 , Hangzhou 310058, China
3. Finnish Geospatial Research Institute 3 , Espoo 02151, Finland
4. College of Information Science and Electronic Engineering, Zhejiang University 4 , Hangzhou 310058, China
5. Shanghai University for Science and Technology 5 , Shanghai 200093, China