1. a State Key Laboratory of Remote Sensing Science, Jointly Sponsored by the Institute of Remote Sensing Applications of the Chinese Academy of Sciences and Beijing Normal University , Beijing , PR China
2. b Faculty of Computing, London Metropolitan University , London , N7 8DB , UK
3. c School of Geography, Beijing Normal University , Beijing , PR China
4. d Institute of Forest Resource Information Techniques, Chinese Academy of Forestry , 100091 , Beijing , PR China