This paper compares different data processing techniques for FTS with the aim of assessing the feasibility of a spectrometer leveraging on standard DAC boards, without dedicated hardware for sampling and speed control of the moving mirrors. Fourier transform spectrometers rely on the sampling of the interferogram at constant steps of the optical path difference (OPD) to evaluate the spectra through standard discrete Fourier transform. Constant OPD sampling is traditionally achieved with dedicated hardware but, recently, sampling methods based on the use of common analog to digital converters with large dynamic range and high sampling frequency have become viable when associated with specific data processing techniques. These methods offer advantages from the point of view of insensitivity to disturbances, in particular mechanical vibrations, and should be less sensitive to OPD speed errors. In this work the performances of three algorithms, two taken from literature based on phase demodulation of a reference interferogram have been compared with a method based on direct phase computation of the reference interferogram in terms of robustness against mechanical vibrations and OPD speed errors. All methods provided almost correct spectra with vibrations amplitudes up to 10% of the average OPD speed and speed drifts within the scan up to 20% of the average, as long as the disturbance frequency was lower than the reference signal nominal one. The developed method based on the arccosine function keeps working also with frequencies of the disturbances larger than the reference channel one, the common limit for the other two.
This paper is devoted to the miniaturized Fourier Transform Spectrometer “MicroMIMA” (Micro Mars Infrared
MApper) design. The instrument has been designed for the spectral characterization and monitoring of the Martian
atmosphere, bound to investigate its composition, minor species abundances and evolution during time. The spectral
resolution of MicroMIMA is of 2 cm-1 (with the option to be extended up to 1 cm-1) that allows to recognize the spectral features of the main elements of interest in the atmosphere and in particular to assess methane abundance with ppb
resolution. The instrument configuration has been optimized in order to achieve the highest sensitivity in the 2 to 5 μm
spectral range, along with the reduction of noise, i.e. the Signal-to-Noise Ratio (SNR) has been used as figure of merit.
The optimization has been carried-out under the constraints of instrument mass, volume, power consumption and
spectral resolution. For the proposed optical layout evaluation of the theoretical SNR for different measurements was
performed accounting both for laboratory observations on Earth and acquisition of Martian atmosphere spectrum during
the mission. Moreover, the instrument trace gas detection capability was evaluated.