The Terra Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Surface Radiance TIR (AST_09T) is generated using the five Thermal Infrared (TIR) bands (acquired either during the day or nighttime) between 8 and 12 µm spectral range. It provides surface-leaving radiance for the TIR bands at a spatial resolution of 90 meters, which includes both surface-emitted and surface-reflected components. It also provides the downwelling sky irradiance values (in W/m2/µm) for each of the TIR bands. This product is atmospherically corrected, and the surface-leaving radiance is of known accuracy and valid only for clear-sky scenes (cloud-free pixels). This atmospherically corrected product provides the input for generating two other higher level products: surface spectral emissivity and surface kinetic temperature.

The algorithm to correct atmospheric effects involves two elements. First, it uses a radiative transfer model—the Moderate Resolution Transmittance Code (MODTRAN)—which can estimate the magnitude of atmospheric emission, absorption, and scattering. MODTRAN calculates atmospheric transmittance and radiance for frequencies from 0 to 50,000 cmˉ¹ at moderate spectral resolution. Second, it identifies and incorporates all the necessary atmospheric parameters applicable to the location and time for which the measurements require correction, including temperature, water vapor, elevation, ozone, and aerosols.

Known Issues

• Level 2 products that are on the international date line/anti-meridian have incorrect bounding coordinates for the UTM zone defined in the file metadata.