Accuracy of ASTER Level-2 thermal-infrared Standard Products of an agricultural area in Spain

The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) collects five-channel thermal-infrared images that are calibrated, corrected for atmospheric effects, and then converted to land surface temperature and emissivity products by the ASTER Temperature/Emissivity Separation (TES) algorithm. TES scales low- and high-contrast surfaces differently, and has been validated over water (low contrast) and rock (high contrast). Performance of TES over agricultural areas, however, has not been evaluated specifically. To address this issue, field measurements of “ground truth” were made over bare soil in addition to green grass, alfalfa and corn, at an agricultural research site in Spain during two coincident campaigns (SPectrA Barrax Campaign, or SPARC, and Exploitation of AnGular effects in Land surface, or EAGLE) during an ASTER overflight. Comparison of the ASTER Standard Products for land surface temperature (AST-08) and emissivity (AST-05) with ground measurements for the crops (corn and barley, plus grass) showed that accuracies of ± 1.5 K and ± 0.01, respectively, were achieved there. However, bare soil was assessed incorrectly by TES as having high emissivity contrast, leading to inaccurate scaling and low apparent emissivities.