Concerning with the complex characteristics of the arid, semi-arid terrain surface, such as undulating topography, un-unique land use/covers and less vegetated land surface, etc. the N’95 model integrated with remote sensing techniques for the estimation of actual evapotranspiration was modified and improved with the focus on the estimation of the net radiation received by surface considering the influence of slope and aspect to the solar shortwave irradiance and surface long-wave irradiance. In addition to that, albedo, displacement height, roughness length for momentum, roughness length for heat, the diabatic correction factors for momentum and heat, the resistance to heat flow in the boundary layer directly ediately above the soil surface in the original N’95 model were modified with new approaches to enable the application of the model more easier in operation and much accurate in computation in terms of specific terrain surface conditions. The instantaneous evapotranspiration was estimated with the modified N’95 model by using the Landsat ETM+ data for an experimental study site located on the conjuncture area of Shaanxi, Gansu and Ningxia where the terrain surface is very undulating with less vegetation developed, heavy soil and water loss loess plateau. And then the spatial pattern of the instantaneous evapotranspiration was analyzed. Actual instantaneous evapotranspiration of 3033 verification points of the study area was calculated with the extra resistance method to compare with the modified N’95 model estimated, which suggested that the modified N’95 model can be used for the accurate estimation of evapotranspiration in arid and semi-arid rugged terrain area covered by sparse vegetation.
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