The GVG(GPS，video and GIS)instrument(patent number:ZL01 144228.X)integrates a video capture card,a GPS receiver,and GIS to co11ecting infor-mation on the proportions of different crops in the total area of a field．
Information on the ground from field surveys makes heavy demands on staff,time,and cost．Field data cannot be co11ected efficiently Without appropriate equipment．The GVG，on the other hand,using automatic data loggers as on-board instruments，can obtain a mass of field data in a short time．The GVG has made the process of data co11ection simpler,more efficient and cheaper.The GVG provides the facility to review every picture recorded during the field sampling：if a picture does not Show arable land，it is to be discarded．Theproportions of different crops are also recorded．Once all the pictures for a transact line are reviewed．the proportion of each crop can be calculated．The overall proportions within a county can be calculatedfrom all the transact 1ines within that county，and so on for anyother administrative unit．
Use of the GVG Standardized the process of co1lecting field data and improved its quality through Strict quality contro1 at every single step in the process．The GVG has been used to obtain in formation on the Shares of different crops in the total sown area across the entire country since 1999．EXtensive valida- tion shows the accuracy of the GVG to be 95% for the main crops including wheat，rice,maize，and soybean．
By virtue of its video-sampling function and GIS-analyzing capablity，the GVG has broadenied its field of app-lication and is now Widely used in investigations of resources，disasters，the environment，and so on．The water resource departments can estimate the water level and disaster degree in real time with the system，which makes it possible for them to provide more precise reports more quickly to the commanding department，in turn making it possible to make more informed decisions and reduce the extent of damage from a disaster．Take the investigation of a disaster，for example．If GVG is used to gather information around the region severely hit by the disaster and the image from the system to- gether With the coordinates sent to the analyzing centre in real time through the Internet，decision- maker's can assess the extent of the disaster immediately．Departments dealing with the conservation of soil and water can use GVG to monitor the effect of treatment in a small watershed as well as to supervise and evaluate bio1ogical treatmelnt measures．