Validation of the ASTER thermal infrared surface radiance data product

The advanced spaceborne thermal emission and reflection radiometer (ASTER) is a 14 channel high spatial resolution instrument selected for flight on the EOS AM-1 platform. This instrument has a 60 km pointable cross-track swath and five thermal infrared channels between 8 and 12 micrometers with 90 m spatial resolution. Correction for the effect of atmospheric attenuation and emission will be made using a radiative transfer model and atmospheric parameters either from the EOS AM-1 platform instruments MODIS (moderate- resolution imaging spectroradiometer) and MISR (multi-angle imaging spectroradiometer) or temperature and moisture profiles from global numerical assimilation models. The correction accuracy depends strongly on the accuracy of the atmospheric information used. To provide an objective assessment of the validity of the atmospheric correction in situ measurements of water surfaces under a variety of atmospheric conditions will be used to estimate the surface leaving radiance at the scale of an ASTER pixel. The procedure will use an array of continuously recording temperature buoys to establish the bulk water temperature, broadband radiometers to determine the near surface water temperature gradient and radiosonde and sunphotometer measurements and a radiative transfer model to deduce the sky irradiance. These measurements and the spectral emissivity of the water will be combined with the relative system spectral response to provide an estimate of thermal infrared surface leaving radiance for each ASTER thermal channel. An example of this approach using a multichannel thermal aircraft scanner as a stand in for ASTER is described. It is expected this approach will provide estimates of surface radiance accurate, in temperature terms, to better than 1 K.