Modelling evapotranspiration using the surface energy balance systems (sebs) and landsat tm data (rabat region, morocco)

Abstract

Modelling and understanding the surface energy balance is important for assessing the re-distribution of moisture and heat in soil and atmosphere. The Surface Energy Balance System (SEBS) estimates turbulent heat fluxes using satellite earth observation data in the visible, near infrared, and thermal spectral domain. SEBS is capable of estimating atmospheric turbulent fluxes and surface evaporation from point to continental scale with reasonable accuracy. Validation of SEBS has been done on a limited set of case studies, which were either on field scale or regional scale. This study aims at validating the use of SEBS for a mesoscale catchment of 270 km2, because this spatial scale is of great interest for many hydrological applications such as erosion modelling, groundwater modelling, crop growth modelling, etc. During a six-week field campaign in August and September 2003 all necessary input data for SEBS were acquired in the community of Sehoul in the province of Sala al Jadida about 20 km south-east of Rabat (Morocco). The fieldwork consisted of measuring meteorological parameters (pressure, temperature, humidity, wind speed, downward solar radiation) at a representative reference location and various soil moisture samples were collected and analysed. Radiance and reflectance data acquired by the Landsat Thematic Mapper 5 sensor were combined with the field measurements to derive land surface physical parameters (albedo, emissivity, temperature, vegetation coverage, etc.). In addition, a digital elevation model from the Shuttle Radar Topography Mission (SRTM) was used in the model. The SEBS algorithm was implemented in the GIS-based PCRaster Environmental Modelling Language. After processing all the inputs, the model results in evaporative fraction and evapotranspiration maps. SEBS was validated with a 1D evapotranspiration model based on temporal soil moisture measurements that were taken with Time Domain Reflectometry (TDR) at three depths (5, 15 and 35 cm) and at ten locations representing common land use, soil and slope combinations of the study area. The suitability of SEBS for modelling evapotranspiration in mesoscale catchments will be discussed here. Furthermore, suggestions for improvement of the model will be given