Abstract: A method for improving the sensitivity of a Fourier transform infrared (FTIR) spectrometer, especially one which is mounted on a movable platform, includes the step of obtaining a background spectrum and an analytical spectrum from an interferogram, and determining the absorption spectrum from the analytical spectrum and the background spectrum. Then, a classical least squares analysis is applied to the absorption spectrum, with reference to a reference spectrum. The classical least squares analysis removes the bias term, and the first and the second-order correction terms related to frequency from the measured absorption spectrum. The method preferably includes two feedback paths in which the background spectrum used in the analysis is derived from a current background spectrum and previously occurring, co-added background spectra using a weighted average approach. The other feedback path involves using one or more alternative reference spectra should a saturation condition exist.