Estimating Actual Evapotranspiration Using RS and GIS

摘要

Evapotranspiration, a major component in terrestrial water balance and net primary productivity models, is difficult to measure and predict. Remote sensing cannot provide a direct measurement of evapotranspiration (ET) but it can provide a reasonably good estimate of Evaporative Fraction (EF), defined as the ratio of ET and available energy. Recent studies have successfully estimated EF using a contextual interpretation of radiometric surface temperature (To) and normalized difference vegetation index (NDVI) such as from the Advanced Very High Resolution Radiometer (AVHRR) onboard NOAA-14 satellite and Moderate Resolution Imaging Spectroradiometer (MODIS), onboard EOS Terra satellite, sensors to estimate ET over large areas. This study compares AET from MODIS and AVHRR applied to a mountainous river basin in Indian Himalayas. Surface Energy Balance (SEBAL) has been used for estimating Actual Evapotranspiration (AET) in the region. In this paper, remote sensing data are used to evaluate the surface albedo, net radiation, ground heat flux, sensible to estimate evapotranspiration and surface conditions using energy balance approach. Being a mountainous basin, an attempt has been made to consider terrain effects in estimating net radiations. Results showed that AVHRR gives an average value whereas MODIS data gives better results since resolution of MODIS is better than that of AVHRR.