MULTI-RESOLUTION REMOTE SENSING DATA AND GIS APPLICATIONS FOR RETRIEVAL OF SPATIAL EVAPOTRANSPIRATION AND SURFACE ENERGY FLUX COMPONENTS OVER THE EAST AFRICAN RIFT BASIN

There is growing interest in using remote sensing data to characterise hydrological components over heterogeneous terrain. Quantification of evapotranspiration, ET, which is attributed to flux in latent heat, is essential in understanding the interaction of energy components for hydrological modelling and as a guide for water resources management practices. Remote sensing becomes important tool in estimating these components in areas suffering from data scarcity (for example, the Ethiopian rift) or areas that only have point measurements (non-spatial representation). A modified algorithm has been developed to process data extracted from remote sensing. And the VDEM (Vegetation Dependable Energy balance Model) algorithm is implemented to estimate the spatial variation of evapotranspiration ($ET$) for the Ethiopian rift. The surface and atmospheric energy components such as net short wave energy, net long wave energy, surface temperature, Soil heat flux, and Sensible heat flux have been estimated using the energy balance principles. The computation involved the Landsat-ETM+ (for evaluating energy components using the VDEM over the region), NOAA-AVHRR (for the precipitable water content using the Split Window Algorithm (SWA)) and ASTER DEM (for attitude cooling effect corrections and atmospheric pressure estimation). Emissivity, sensible heat, soil heat flux, and the surface heterogeneity of the area has been estimated as a function of the land cover condition which is assessed using the land use land cover conditions and vegetation indices (NDVI, SAVI and LAI). Regression is performed for surface roughness estimation from analysis of a vegetation index in aid of aerodynamic resistance evaluation. This paper demonstrates the utility of high resolution remote sensing data in estimating the spatial surface temperature over heterogeneous terrain using calibrated spectral radiance and the actual ET from energy components using high level programming language. The paper also presents the influence of vegetation cover and altitude in variation of ET across the Northern Ethiopian Rift.