Mapping evapotranspiration in the Indus Basin using ASTER data
Abstract:Conventional methods that use point measurements to estimate evapotranspiration are representative only of local areas and cannot be extended to large areas because of heterogeneity of landscape. To overcome this difficulty, remote sensing has proven to be the most suitable approach for large area estimation of evapotranspiration because remote sensing data can provide representative parameters such as radiometric surface temperature, albedo and vegetation index. The heterogeneity is more prominent in the Indus Basin as more than 80% of farmers have land holdings less than 4 ha, and within these holdings, two or three different crops are usually grown. The limitation of most remote sensing based procedures to estimate evapotranspiration is the measurements of large number of crop-specific and climatic parameters, which are not only difficult to obtain but also require considerable field work, equipment and therefore involve much expenditure. The purpose of this study was to present a simple methodology that requires minimum ground observations for estimation of evapotranspiration to test the reliability of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data for estimation of evapotranspiration in the Indus Basin. The methodology is based on surface energy balance to estimate sensible and latent heat fluxes by combining remotely sensed data from ASTER with common meteorological data. The various components of surface energy balance were computed during satellite overpass and 24-h integrated fluxes were derived for the full ASTER scene acquired over the lower Rechna doab region of the Indus Basin. The surface brightness temperatures were derived from thermal band 13 and NDVI from two VNIR bands of the ASTER. Evapotranspiration values from the maize field in the Indus Basin, as estimated using ASTER data at Shahkot, Jaranwala and Satiana locations, were estimated as 2.05, 2.77 and 2.32 mm day-1, respectively. The estimated evapotranspiration was compared with evapotranspiration computed at three different locations using CROPWAT software and was found to be in close agreement.
Document Type: Research Article
Publication date: 2007-01-01