1 School of Remote Sensing and Information Engineering,Whuhan University,129 Luoyu Road,Wuhan 430079,China;2 Department of Surveying,Heilongjiang Engineering Institute,999 Hongqi Road,Ha'erbin 150008,China;3 Hazard Monitoring & Prevention Research Center,Wuhan University,129 Luoyu Road,Wuhan 430079,China;4 Institute of Geographical Sciences and Natural Resources Research,CAS,11A Datun Road,Chaoyang District,Beijing 100101,China