1. State Key Laboratory of Remote Sensing Science, Research Centre for Remote Sensing and GIS, Beijing Normal University, Beijing 100875, China
2. School of Geography, Beijing Normal University, Beijing 100875, China
3. Department of Geology and Geography, West Virginia University, Morgantown, WV 26506, USA
4. Department of Geography, Remote Sensing Laboratories, University of Zurich, Zurich 8057, Switzerland