Evaluation of Remote Sensing Based Surface Energy Balance System (SEBS) Algorithm for Estimation of Evapotranspiration in Eastern Ethiopia A
No Thumbnail Available
Date
2016-05
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Addis Ababa Universty
Abstract
The basic objective of this study is evaluating remote sensing based SEBS model to estimate evapotranspiration in eastern Ethiopian landscape. The study has utilized cloud free MODIS level 1B images for dry season and other composites for wet season analysis. In the preprocessing phase raw MODIS scenes are converted to reflectance and radiance; brightness temperature is estimated; water vapor is estimated using ratio technique and atmospheric correction is undertaken by using SMAC model. After these, bio-physical parameters for SEBS model are estimated. Integration of these datasets with downward surface short web flux energy, sun-satellite geometry data and other meteorological data, surface energy fluxes and ET have been estimated. For comparative analysis, ET is estimated from 18 ground based meteorological observations using FAO-PM technique and composited Meteosat Second Generation (SAF MSG) ET product is utilized. Results have showed that in study site at the dry season SEBS model yields mean ET values that range from 3.74(±1.54) to 4.05(±1.72) mm day-1. At the summer season, mean ET values range from 2.9(±1.7) to 3.8(±2.2). These values vary across the land cover classes in the study area. Undertaken comparative analysis showed that SEBS model underestimates ET value than FAO-PM and overestimates ET value than SAF MSG ET product. Though this is a general trend, there exist hybrid pattern in different parts of eastern Ethiopia. In the dry season, SEBS brought proxy values with FAO-PM and SAF MSG products at areas that have better vegetation cover. In most arid and semi-arid expanses of the study site, SEBS has brought extremely underestimated values than FAO-PM values while with SAF MSG, there is better coinciding values though not with similar manner. In the summer season, with advent of vegetation greenness regeneration following summer rain, SEBS model has brought values greater than dry season estimates in arid and semi-arid environment. The model is also sensitive for aerodynamic roughness length derivations. Therefore, the study can argue that though SEBS provide good ET estimates, it can be affected by vegetation characteristics and aerodynamic roughness length derivations. Accordingly, comparison of SEBS results with direct measurements, precautions while deriving roughness length and further model sensitivity study for other model inputs is recommended.
Key words: SEBS model, Evapotranspiration, Remote sensing, FAO-PM, Eastern Ethiopia
Description
Keywords
SEBS model, Evapotranspiration, Remote sensing, FAO-PM, Eastern Ethiopia