Fourier Transform Interferometry

The basic Michelson interferometer, as used for Fourier transform spectroscopy, is analyzed in this report. The principles of operation are explained, and its inherent limitations are shown. An original analysis of apodization, for the case of an off-axis detector field-of-view, is included in an appendix. Practical limitations of real instruments are also analyzed. These include misalignment, wavefront error, and noise sources. In another appendix, the use of retroreflectors in the interferometer is analyzed, and the effect of lateral displacement of a retroreflector is compared to that of mirror tilt in a plane-mirror interferometer. Special attention is given to sources of noise in the Fourier transform spectroradiometer, and expressions are derived for noise-equivalent radiance from these sources. The performance of a Fourier transform spectrometer is compared with that of a filter-wheel spectrometer having the same optical aperture and spectral resolution. The mathematical treatments in this report are sufficiently detailed that they should be easy to follow, once the optical principles are grasped. Some numerical calculations are included, based on the specifications of the proposed GOES High-Resolution Interferometer Sounder (GHIS).