Research On A Model Of Regional Crop Evapotranspiration Based On3S Technology

Through reviewing the research achievement of crop evapotranspiration at present, the researchstatus of different spatial-temporal scale models and the scale conversion methods of cropevapotranspiration was described, and the development trend of research on crop evapotranspirationmodel was hereby forecasted. First, based on remote sensing data, digital elevation model and GIStechnology, new spatial interpolation method was established to realize the spatial scale conversion ofcrop evapotranspiration from the precise point scale to the large scale. Then, on the basis of remotesensing data, accurate instantaneous crop evapotranspiration model was built to realize the temporalscale expansion of crop evapotranspiration by a temporal scale expansion method based on cropcoefficients. Finally, a comprehensive and operational model of crop evapotranspiration was establishedthrough the spatial-temporal scale conversion method. At the same time, the main research content ofthis article was proposed and completed as follow.Base on Bowen Ratio-Energy Balance Method, the spatial variation coefficient of cropevapotranspiration was deduced to realize the spatial-temporal scale conversion of cropevapotranspiration. This method not only took full advantage of the relatively accurate point data tomake sure that crop evapotranspiration was of high precision, but also was able to scientifically andaccurately describe the spatial variation of crop evapotranspiration in smaller area just using the spatialvariability information reflected by remote sensing data instead of the precision inverse parameters. Sothe work intensity of processing the previous remote sensing data reduced as well as the workload andcosts.Using the method of estimating reference evapotranspiration based on the Penman-Monteithformula, the relationship between the daily reference evapotranspiration (ETod) and the sum of24hourly reference evapotranspirations within a day (ET0dh) was researched. It was found that thereexisted a significant linear relationship between ETodand ET0d（hETod=k×ET0dh）and the k approached to1. This indicated that the method of estimating reference evapotranspiration based on thePenman-Monteith formula met the feature that each hourly crop coefficient within a day was the same,and the daily crop coefficient did not strictly equal to but had a significant linear correlation with thehourly crop coefficient (kch=k×kcd). Therefore, the ratio of ETodto ET0dhcan be used to establish thetransformational relation between kcdand kch, which can improve the temporal scale expansion methodof crop evapotranspiration based on crop coefficients.Combining3S technology and the spatial-temporal scale conversion method mentioned above, amodel of regional crop evapotranspiration based on3S technology (ETsystem Model) was built. Thenfield experiment data and remote sensing data were used to realize the application and verification ofETsystem Model in detail. The result showed that the ETsystem Model could accurately estimate cropevapotranspiration in different spatial-temporal scales, aswell as economically and flexibly achieve the spatial-temporal scale conversion of crop evapotranspiration in Ren Min Sheng Li Qu irrigation district.Its economy and flexibility were manifested in convenient data acpuisition, easy spatial-temporal scaleconversion and easy parameterization.