1. University of the Chinese Academy of Sciences, Beijing, People’s Republic of China
2. Chinese Academy of Sciences, Aerospace Information Research Institute, Beijing, People’s Republic of China
3. Faculty of Geo-Information Science and Earth Observation, University of Twente, Enschede, The Netherlands
4. Institute of Atmospheric Pollution Research, National Research Council, Florence, Italy
5. Key Laboratory of Virtual Geographic Environment (Ministry of Education), Department of Geography, Nanjing, Nanjing Normal University, Jiangsu, People’s Republic of China