Accurate knowledge of the instrument lineshape (ILS) of Fourier transform infrared (FTIR) spectrometers is required for proper measurement analysis. An ILS is instrument- and spectrally-dependent and can substantially deviate from the ideal ILS. The ILS of a low-resolution FTIR has been determined for spectral resolutions of 1, 2, 4, 8, 16, and 32 cm−1. Each ILS was recovered with the retrieval software LINEFIT. Using the recovered ILS, transmissivity spectra of carbon monoxide (CO) and carbon dioxide (CO2) were calculated using the HITEMP2010 spectral database. These spectra were then compared with (1) idealized spectra (calculated using HITEMP2010 and the ideal lineshape) and/or (2) measured spectra from the FTIR to analyze both the accuracy of LINEFIT and the systematic error that can result from assuming the ILS to be ideal.

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