1. State Key Lab. of Resources and Environment Information System; Institute of Geographical Sciences and Resources Research Chinese Academy of Sciences; Beijing 100101 China
2. Agrifoods Development Branch Dep. of Natural Resources; Corner Brook NF A2H6J8 Canada
3. Potato Research Centre; Agriculture and Agri-Food Canada; Fredericton NB E3B4Z7 Canada
4. Dep. of Geography; Univ. of Wisconsin; 550 N. Park St. Madison WI 53706
5. State Key Lab. of Remote Sensing Science; Institute of Remote Sensing Applications Chinese Academy of Sciences; Beijing 100101 China
6. Dep. of Geology and Meteorology; Kean Univ.; 1000 Morris Ave. Union NJ 07083