Research And Implementation Of Regional Evapotranspiration Based On Remote Sensing

There is the phenomenon of evaporation anywhere on earth. The surface of the earthobtains energy through solar radiation while the energy consumption is mainly processed bywater evaporation. Water in the atmosphere is converted to the surface by the way of gas,liquid or solid, like rain, snow, fog, frost, hail and so on.70%of the precipitation will beevaporated into the atmosphere through the surface water evaporation, soil evaporation andvegetation transpiration. In the process of water exchange, energy is also transmitted alongwith water exchange. Water exchange between the surface and the atmosphere actuallyinvolves matter and energy at the same time. In this process, the evaporation is an integralpart of water and energy balance between surface and the atmosphere.Influenced by time change, terrain, climate, vegetation, unequal space distributionfactors and so on, evapotranspiration owns a strong time variability and spatial variability.With their calculation results applied to a small area, traditional methods such as ripplemethod, aerodynamic method, and eddy correlation method are all based on point source tocalculate the evapotranspiration, and the study of regional evapotranspiration is difficult toachieved. Remote sensing technology can provide a wide range of long time series surfaceinformation, which can carry on the overall description of terrain feature information.Continuous in time and space, this kind of technology can extend the observation to lager area,which break the limitation of traditional method and further make the estimate moreconvenient and widely used.Based on SEBAL model, applying Landsat5TM image in combination with DEM dataand meteorological data, this thesis selects Zhengning county of Qingyang city, Gansuprovince as the research area and studies Remote sensing estimation research of areaevapotranspiration. In this research, the author uses ArcGIS and ENVI software to processdifferent data, such as the mosaic, cutting and vector grid conversion of remote sensing imageand DEM data, and requires a lot of intermediate data in evaporation estimation. In terms ofTM image preprocessing, the thesis mainly studies the principle of remote sensing imageradiation correction and implements the radiation calibration and FLAASH atmosphericcorrection. Besides, the thesis achieves the raster and vector transformation of DEM data, andthe generated point elements involve in interpolation of inverse distance weighting methodbased on DEM meteorological data, which can predict meteorological data and make up forthe lack of meteorological data in the study area. And the author carefully analyzes theprocess of evaporation estimation, and successfully achieves the inversion of surfaceparameters and the energy flux. Finally, the author estimated daily evaporation in the study area, and the results are verified and analyzed.Through the study, it can be found that using remote sensing technology to estimateregional evaporation can more easily access research data, and the process of using theSEBAL model calculation is clear. At the same time, due to the instantaneity of data obtain,empirical formula of inversion of surface parameters and energy flux is more simplified,which make the error of the final result bigger. Therefore, further studies are needed in orderto get a better estimate of regional evaporation method, make a contribution for human beingto deeply understand their own ecological environment.