Evaluation of the sensitivity to mechanical vibrations of an IR Fourier spectrometer

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Abstract
This article presents an experimental and theoretical investigation of the sensitivity to mechanical disturbances of a Fourier-transform infrared spectrometer, the Planetary Fourier Spectrometer, currently orbiting around Mars onboard ESA Mars Express orbiter. A theoretical analysis has been performed in order to highlight the expected effects of the vibrations, then laboratory tests have been designed and carried out for instrument characterization. The two classical types of disturbance effects were expected in the case of mechanical vibrations: the interfering type, leading to an additive contribution to the interferograms, and the modifying type, which changes the interferometer sensitivity. Both effects have been evidenced in the experimental tests and the instrument sensitivity derived; moreover, the effects on the spectra, which are the Fourier transform of interferograms, are highlighted and characterized. The effects of both harmonic and random broadband spectrum disturbances have been considered. While the broadband disturbances increase uniformly the noise, harmonic disturbances produce localized effects in the spectra and replicas of the spectral features with wave-number shifts proportional to disturbance frequency. It has also been highlighted that, the disturbances from mechanical vibrations being uncorrelated with the interferometric signals, by spectrum averaging, like all the other noise sources, they can be reduced. Methods for spectrum diagnostics and for increasing the signal-to-noise ratio in vibration-affected spectra are proposed as well.