1 Key Laboratory of Digital Earth Science, Institute of Remote Sensing and Digital Earth, Chinese Academy of Sciences, Beijing 100094, China. Electronic address: lull@radi.ac.cn.
2 Key Laboratory of Digital Earth Science, Institute of Remote Sensing and Digital Earth, Chinese Academy of Sciences, Beijing 100094, China. Electronic address: hdguo@radi.ac.cn.
3 European Commission, Joint Research Centre (JRC), Directorate for Space, Security & Migration, Ispra I-21027, Italy.
4 Key Laboratory of Digital Earth Science, Institute of Remote Sensing and Digital Earth, Chinese Academy of Sciences, Beijing 100094, China.