Instrument line-shape modeling and correction for off-axis detectors in Fourier-transform spectrometry

Spectra measured by off-axis detectors in a high-resolution Fourier-transform spectrometer are characterized by frequency scaling, asymmetry and broadening of their line shape, and self-apodization in the corresponding interferogram. For a narrow-band input spectrum and a specified detector geometry, a formalism is presented that accounts for these effects with separate terms. Some of the terms are used to correct the larger off-axis effects as part of the calibration. The remaining terms are used to model the residual effects with the on-axis instrument line shape. We extend this approach to the broadband case using filter banks. The technique is applied to simulated spectra for the Tropospheric Emissions Spectrometer. This approach is shown to maintain a radiometric accuracy to less than 0.1%.