SPIE Proceedings [SPIE Geoinformatics 2008 and Joint Conference on GIS and Built Environment: Monitoring and Assessment of Natural Resources and Environments - Guangzhou, China (Saturday 28 June 2008)] Geoinformatics 2008 and Joint Conference on GIS and Built Environment: Monitoring and Assessment of Natural Resources and Environments - Estimation of net primary productivity in North Tibet Plateau by integrating CASA model with MODIS data