1. a Kansas Applied Remote Sensing (KARS) Program and Department of Geography , University of Kansas , Lawrence, KS 66045, USA
2. b Natural Resource Ecology Laboratory , Colorado State University , Ft Collins, Colorado 80523, USA E-mail:
3. c Department of Geography , University of Kansas , Lawrence, Kansas 66044, USA E-mail:
4. d Institute of Natural Resources , Beijing Normal University , Beijing 100 851, China E-mail: