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SEBS module BEAMS: A Practical Tool for Surface Energy Balance Estimates from Remote Sensing Data.

Lichun Wang(1), Gabriel N. Parodi(1) and Zhongbo Su(1)

(1) ITC, Hengelosestraat 99, 7500 AA, Enschede, Netherlands

Abstract

The SEBS algorithm (Su, 2002) is an extension of the SEBI concept with a dynamic model for thermal roughness (Su et al., 2001), the Bulk Atmospheric Similarity (BAS) theory (Brutsaert, 1999) for PBL scaling and the Monin-Obukhov Atmospheric Surface Layer (ASL) similarity for surface layer scaling. As such SEBS can be used for both local and regional scaling under all atmospheric stability regimes thus providing a link for radiometric measurements and atmospheric models at various scales. SEBS consists of a set of tools for the determination of the land surface physical properties and state variables, such as albedo, emissivity, temperature, vegetation coverage etc. from spectral reflectance and radiance; an extended model for the determination of the roughness length for heat transfer (Su et al., 2001); and a new formulation for the determination of the evaporative fraction from the energy balance at limiting cases.

SEBS requires as inputs three sets of information. The first set are land surface properties derived from RS and some additional ground data (albedo, emissivity, temperature, fractional vegetation, LAI, and the height of the vegetation or roughness height, where NDVI could be used as a surrogate). The second set is related to meteorological data or maps of air pressure, air temperature, humidity, and wind speed at a reference height (PBL or ASL). This data can also consist of estimates by a large scale meteorological model. The third data set deals with incoming SW and LW radiation either from direct measurements, model output or parameterization. SEBS was validated under a wide range of environmental and climatological conditions; it was tested versus AET rates in a semiarid inland basin in NW China (Li, 2001; Su et al., 2003a), and for drought disaster monitoring (Su et al., 2003b). It evaluated well as compared with other remote sensing techniques over irrigated fields (Norman et al., 1995; Zhan et al., 1996; Kustas and Norman, 1999; Su et al,. 2001, Su, 2003).

SEBS is now implemented as a “BEAM” (ESA software tools) module for AATSR (Su and Wang, 2007). AATSR is radiometrically calibrated and atmospherically corrected (using the SMAC module in BEAM) to attain the information required for the first set of inputs (pre-processing). Meteorological information and radiatives maps are incorporated in a second interface were the SEBS algorithms is launched using the ILWIS as an engine. This result in maps of Rn, L, H, G, Lwet limit, Ldry limit, evaporative fraction, AET instantaneous and AET daily, and complementary files as standard outputs.

 

Workshop presentation

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry