The instrumental line shape of the atmospheric chemistry experiment Fourier transform spectrometer (ACE-FTS)

Accurate modeling of the instrumental line shape (ILS) of a Fourier transform spectrometer (FTS) is crucial for minimizing systematic errors in the analysis of FTS measurements. Isolated spectral features having widths much less than the ILS width can be used to determine a representation for the ILS. The instrument modulation function at a particular wavenumber can be calculated from the Fourier transform of an isolated spectral feature. Accounting for known contributions from the finite field of view and the shape of the spectral feature in the infinite resolution spectrum, one can directly observe the contribution from all additional sources of self-apodization to the instrument modulation function. This simplifies determination of the appropriate empirical function(s) to best characterize these additional self-apodization effects, alleviating the need to guess at forms for the empirical function. Lines spanning the instrument spectral range are analyzed to determine a wavenumber dependence for the empirical representation. This approach is employed to characterize the ILS for the Atmospheric Chemistry Experiment Fourier transform spectrometer (ACE-FTS), a high resolution (0.02 cm(-1)) satellite-based instrument used for solar occultation studies of the Earth's atmosphere. (C) 2019 Published by Elsevier Ltd.