Application of Thematic Mapper Images to Determine Regional Evaporation from thePlayas in the Western Desert of Egypt

摘要

To estimate actual evaporation from playas or sebkhas, a technique based onanalysis of LANDSAT Thematic Mapper images and field measurements was developed. Surface reflectance and surface temperature are obtained with Thematic Mapper measurements. Effective properties of nonhomogeneous land surfaces, could be derived from the satellite image. This information is applied to classify soils and to determine the transfer of sensible and latent heat into the atmosphere. An algorithm is developed to obtain maps of latent heat flux with measurements of surface reflectance and surface temperature on a pixel by pixel basis. The so obtained values are validated with ground based observations of latent heat flux, obtained by means of the Bowen ratio energy balance method. Combination of daily evaporation values, calculated by means of models to simulate soil water flow through the unsatured zone, with instantaneous latent heat flux values, gives maps of daily and annual evaporation rates. The overall conclusion is that evaporation from playas is significantly higher than previously estimated. This has an important impact on the total regional groundwater development schemes.