Land Surface Temperature derived from Airborne Hyperspectral Scanner Thermal Infrared data

Abstract

The AHS (airborne hyperspectral scanner) instrument has 80 spectral bands covering the visible and near infrared (VNIR), short wave infrared (SWIR), mid-infrared (MIR), and thermal infrared (TIR) spectral range. The instrument is operated by Instituto Nacional de Técnica Aerospacial (INTA) and it has been involved in several field campaigns since 2004. The main goal of this paper is to analyze the feasibility of retrieving land surface temperature from the 10 AHS thermal infrared bands, from 71 to 80, located in the region between 8 and 13μm. For this purpose, three different methods have been considered: (i) the single-channel method, which uses only one thermal band; (ii) the split-window method, which uses a combination of two thermal bands; and (iii) the TES (temperature and emissivity separation) method, which needs at least four thermal bands. The calibration of the AHS thermal bands and the algorithms have been tested with in situ measurements collected in the framework of the SPARC (Spectra Barrax Campaign) and EAGLE (Exploitation of AnGular effects in Land surfacE observations from satellites) field campaigns, which took place simultaneously in the agricultural area of Barrax (Albacete, Spain), and also in the framework of the AGRISPECTRA field campaign, carried out over an olive orchard in Córdoba (Spain), in July 2004. AHS flights were conducted at two different altitudes, 975m and 2745m above ground level. The results show that AHS bands 71 (8.18μm), 72 (8.66μm), and 73 (9.15μm) were affected by a calibration problem. Taking into account that AHS bands 74 (9.60μm) and 80 (12.93μm) are located in an absorption region, bands from 75 to 79 have been finally selected for land surface temperature retrieval. The single-channel method has been applied to AHS band 75 (10.07μm), which shows the highest atmospheric transmissivity, whereas the split-window method has been applied to the combination between bands 75 and 79 (12.35μm), which provides the best results according to simulated data. All the AHS thermal bands ranging from 75 to 79 have been used in the TES method. The tests conducted on the different algorithms used in this study show that single-channel and split-window methods provided similar results, with root mean square errors (RMSE) between 1.6 and 1.9K. The TES method slightly improved the results, with a RMSE of 1.4K.