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International Journal of Remote Sensing



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A 10-channel infrared (1.25–17.24 mm wavelength) radiometer known as SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) is one of four experiments that will fly on the TIMED (Thermosphere, Ionosphere, Mesosphere, Energetics, and Dynamics) mission that was successfully launched on 7 December 2001. Theoretical models of the relative spectral response (RSR) for each SABER channel were developed during the design and build of the instrument. The RSR calculations were then refined using a component level technique where theoretical predictions of filter transmittance were replaced with measurements from filter witness samples. During SABER ground calibration, full system measurements of RSR were performed using a Michelson step-scan interferometer to present an interferometrically modulated infrared source to the instrument with the resultant interferogram recorded by the instrument detectors. Fourier transform of this interferogram and correction of the resulting spectrum for the spectral output of the interferometer and the transmittance of any intervening optics provide a measurement of the system level RSR. We compare the full system level measurements with the theoretical and component level RSR predictions for both in-band and out-of-band spectral regions. Our results show that the system level method for determining RSR provides the clearest picture of the instrument’s spectral properties.