1. Geography and Environment, University of Southampton, Southampton SO17 1BJ, UK
2. Faculty of Geo-Information Science and Earth Observation (ITC), University of Twente, Enschede 7500 AE, The Netherlands
3. Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Changchun 130102, China
4. School of Electrical and Information Technology, Changchun Institute of Technology, Changchun 130021, China