1. a Laboratory of Remote Sensing Information Sciences , Institute of Remote Sensing Applications , PO Box 9718, Beijing 100101, China E-mail:
2. b TRIO/LSIIT (CNRS UMR 7005) , 5 Bld. Sebastien Brant, 67400 Illkirch, France
3. c Guangzhou Institute of Geography , Guangzhou, 510070 China