Robustness of atmospheric trace gas retrievals obtained from low spectral resolution Fourier-transform infrared absorption spectra

For atmospheric trace gas columns retrievals obtained from ground based Fourier-transform interferometer spectra we study the sensitivity of the retrieval processing chain to changes in the number of points in the recorded interferograms. Shortening an interferogram will alter the leakage pattern in the associated spectrum and we demonstrate that the removal of a relatively small number of points from the interferogram edges creates a beat pattern in the difference of the associated spectra obtained from the original and shortened interferogram. For low-resolution interferometers the beat pattern in the spectra may exceed the noise level and the effect on atmospheric gas column retrievals may be large. Sensitivity of the retrieval algorithm to the length of the underlying interferogram can be reduced by applying a non-trivial apodization such as Norton-Beer. A case study shows the effect on formaldehyde retrievals obtained from low-resolution spectra in Sodankylä and Kolkata.