GVG, a Crop Type Proportion Sampling Instrument
GVG农情采样系统及其应用

GVG instrument is an integration of video capture card,GPS receiver and GIS for collecting the crop type proportions in the field. VIDEO and GPS are integrated into the GIS installed in a notebook. GVG mounted on car or motor takes records with video camera during the movement. The car should not be fast than 40 km/h in order to acquire high quality of pictures. When GVG is working, it records pictures and the position from GPS as well as geographical attributes from GIS data layer, for example county code, into a temporarily database. One person is enough to operate GVG in addition the driver. When fieldwork is done, the GVG provides the function to review every pictures recorded during the sampling. If the picture does not contain the arable land, it shall be discarded, otherwise, the proportion of every crop types will be recorded manually, and the picture will be recorded too. Once all pictures are reviewed for a transect line, it is easy to calculate the proportion of crop types. The crop proportions for a county can be calculated from all transect lines within the county, and the same for stratum. GVG has been used to obtain the crop type proportions of entire country since 1999. The extensive validation shows the GVG can have the accuracy of 95% for main crops, including wheat, rice, maize and soybean. According to the principle of GVG, it has multi-purpose applications, not only on the crop type proportions, but also on environment monitoring for example.