Calibrated Moon radiance values for the 19 HIRS thermal IR filters for all 22 observing epochs, as a function of wavelengths. The arbitrarily-scaled filter curves (NOAA-18/HIRS/4) are overplotted. The peak transmission of these narrow filters is always close to 1. The variation in radiance at a given wavelength is mainly related to the different heliocentric distances of the Moon (ranging from r = 0.985 to 1.018 au) and the large range of phase angles (from −73.1° to +73.8°).