| Estimate the evapotranspiration accuratly has an important guiding significance for the rational allocation of regional water resources, drought monitoring and water resources evaluation.Traditional estimation methods of evapotranspiration limited to the estimation on the discrete points, while on regional evapotranspiration estimation, there are limitations of epitaxial interpolation accuracy was low, poor timeliness and more other shortcomings. In recent years, remote sensing technology developed rapidly, the remote sensing data can provide real-time, periodic and regional ground observation data,with it can estimate the regional evapotranspiration, it has important value for regional water resources planning.In this study with remote sensing technology as the main means, with the eastern agricultural region of Qinghai Province as the study area,using MODIS satellite remote sensing data on August 13,2005,combing with meteorological data such as air temperature,wind speed and vapor pressure and 90 m digital elevation model, from the point of view of the surface energy balance,establish the remote sensing monitoring model of evapotranspiration of eastern agricultural area in Qinghai Province based on SEBAL model through spatial modeling tools in ERDAS imagine9.2,and then using the constructed model calculate the daily evapotranspiration in the study area,and using the calculate result by P-M formula to verify the results estimated. At the same time, analysising the correlations between the evapotranspiration and key surface parameters and topographic parameters of the study area.Through this study, the following conclusions are obtained:(1)The inversion results of main surface parameters: the range of NDVI was from-0.0847 to 0.9257, the average value was 0.5976, the range of vegetation coverage was from 0 to 1, with a mean value of 0.4885; the range of surface emissivity was from 0.9 to 1.0, with a mean value of 0.9819,the range of surface albedo was from 0.0102 to 0.6982,average value was 0.1416, surface temperature range for 276 to 314.65 K, mean for 295.87 K.(2)The inversion results of flux in the energy balance equation: the range of net radiation flux was from 117.2563 to 679.4882Wm/, average value was 237.11552Wm/,the range of soil heat flux was from 104.8362 to 238.8952Wm/, average value was 124.71202Wm/, the range of sensible heat flux was from 0 to 296.9952Wm/,average value was 111.542Wm/, the range of latent heat flux was from 0 to 440.2972Wm/,average value was 248.3522Wm/. Then calculating the evapotranspiration on August 13,2005 of eastern agricultural region in Qinghai Province by method of invariant evaporation ratio,the results was from 0 to 11.5201 mm, average value was 6.07 mm.(3)Using the penman Monteith formula calculated the evaporation and transpiration of reference crop in eastern agricultural region of Qinghai Province for 4.86 mm, multiplied by the crop coefficients obtained the daily evapotranspiration was 4.91 mm, the error between actual evaportranspiration inversed by remote sensing technology and evaportranspiration calculated by P-M formula was 23.6%, and calculated the month evapotranspiration was 132.47mm(4) Analyze the correlation between the the evapotranspiration and surface parameters and topographic parameters in east agricultural region of Qinghai Province, the results shows that the vegetation coverage and slope have a positive correlation with daily evapotranspiration, the correlation coefficients was 0.936 and 0.961 respectively, the temperature has a negative correlation with daily evapotranspiration, the correlation coefficient was 0.388; the relationship between daily evapotranspiration and aspect was more complex, the correlation coefficient was 0.878,in different aspect,the evaportranspiraton was shady slope> semi shady slope(semi sunny slope) > sunny slope. |
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