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Validation of Land Surface Temperatures derived from AATSR data at the Valencia test site

Cesar Coll(1) , Vicente Caselles(1) , Enric Valor(1) , Raquel Niclos(1) , Juan M. Sanchez(1) , and Joan M. Galve(1)

(1) University of Valencia, C/ Dr. Moliner, 50, 46100 Burjassot, Spain

Abstract

Land surface temperatures (LSTs) derived from AATSR data were validated with ground measurements performed at a test site close to Valencia, Spain in a series of experimental campaigns carried out during the summers of 2002-2004. The test site was located in a large, flat and thermally homogeneous area of rice crops showing full vegetation cover. Ground LSTs were measured radiometrically along transects covering an area of 1 km2, concurrently to morning, cloud-free overpasses of Envisat. Four thermal radiometers were used, which were calibrated and inter-compared through the campaigns. Radiometric temperatures were corrected for emissivity effects using field emissivity and downwelling sky radiance measurements. A total number of 17 concurrences of ground measurements and AATSR overpasses were obtained. Ground LSTs ranged from 25 to 31 ºC, with uncertainties between ±0.4 and ±0.9 ºC, the largest part of the uncertainties being due to the spatial variability of surface temperature. The precipitable water of the atmosphere ranged between 1.5 and 3 cm. The ground database was used for the validation of LSTs derived from different split-window algorithms applicable to AATSR data (11 and 12 micron channels at nadir). According to the results of the validation, it can be concluded that the split-window algorithms work well, provided that the characteristics of the area are adequately prescribed, either through the classification of the land cover type and the vegetation cover, or with the surface emissivity. In this case, the AATSR derived LSTs agreed with the ground LSTs within ±1.5 ºC for all 17 concurrences, with small average error or bias (few tenths of degree) and a standard deviation of ±0.7 ºC. These results give confidence to the use of split-window algorithms with AATSR data for the retrieval of LST.

 

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