China Crop Watch System with Remote Sensing
中国农情遥感速报系统

The paper introduces China Crop Watch System with Remote Sensing (CropWatch),including its contents, technical innovation and operational development, validation and future activities. Crop Watch contents 5 components, consisting of crop condition monitoring, crop acreage estimation and yield prediction, grain production estimation, cropping index and crop structure monitoring, and drought monitoring. Each component is described briefly in this paper and detailed in following papers. Since 1998, the CropWatch has been put in operation. Each year, there are 7 monthly bulletins released, covering crop condition, crop acreage and yield, drought, agro-meteorology, cropping index and crop structure, and also grain production. And there are 21 10-days announcements released, covering drought and crop condition. During the operational period since 1998, the technology used by the CropWatch are consistently improved. All AVHRR image from 1991 are processed for calibration and correction precisely which began in 2000, including sensor calibration, zenith correction, cloudy detection and masking, geometric correction, atmospheric correction, BRDF correction,and NDVI and surface temperature calculation. The CropWatch uses both different image and growing profile of NDVI to monitor the crop condition, estimates crop acreage using remote sensing and sampling technique based on stratification. The cluster-sample framework is used to estimate plant proportion with TM and Radarsat image as samples, and transect-sampling framework is used to survey crop type proportion in planted-area. At the same time, The Crop Watch continuously expands its monitoring area. From 1998 to 2003, its monitoring area has been expanded from east China to national wide, to north and south America, to Australia and Thailand. Meanwhile, the Crop Watch continuously expands its monitoring contents, from crop condition monitoring, crop acreage estimation and crop yield prediction, to grain production, crop structure, and cropping index. The Crop Watch has its own validation programme. Each year, a few validation sites have been selected to do the field measurement for verifying specific results. For example, in 1999, Jiangning in South China were Dehui in North China were two sites. The crop LAI every 10 days and crop type proportion have been measured to verify the crop condition and crop acreage. Validation shows that the accuracy are up to 97% for plant proportion and 95 crop type proportion.