1. Cold and Arid Regions Environmental and Engineering Research Institute; Chinese Academy of Sciences; Lanzhou 730000 Gansu China
2. University of Chinese Academy of Sciences; Beijing 100094 China
3. Institute of Environmental Engineering; ETH Zurich; Stefano-Franscini-Platz 3 8093 Zurich Switzerland
4. School of Information Science and Engineering; Lanzhou University; Lanzhou 730000 Gansu China
5. State Key Laboratory of Remote Sensing Science, Institute of Remote Sensing and Digital Earth; Chinese Academy of Sciences; Beijing 100101 China