1. State Key Laboratory of Black Soils Conservation and Utilization, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Changchun 130102, China
2. University of Chinese Academy of Sciences, Beijing 100049, China
3. State Key Laboratory of Remote Sensing Science, Aerospace Information Research Institute, Chinese Academy of Sciences, Beijing 100094, China
4. School of Geographical Sciences, University of Bristol, Bristol BS8 1SS, UK