Analysis method for Fourier transform spectroscopy

Abstract

In the analysis of the interferometric spectrum, an accurate knowledge of instrument line shape is required. The instrument line shape of the interferometric spectrum can be distorted owing to errors in the measured interferogram, which are generally categorized into the intensity error and the phase error. The intensity error that is due to the effect of the field of view, optics misalignment, instrument noise, and smearing effect causes a symmetric distortion of the instrument line shape, and the phase error causes an asymmetric distortion. This paper describes a fast Fourier transform technique for simulating the distortion effects, and the technique is applied to the analyses of atmospheric absorption spectra and laboratory spectra. It is shown that correct information can be retrieved from the distorted spectrum using the nonlinear least-squares method. From analyses of HF absorption spectra obtained in a laboratory and solar CO absorption spectra obtained from a balloon-borne interferometer, it is found that the retrieved amount of absorbing gas is less than the correct value in most cases if the interferogram distortion effects are not included in the analysis.