Optical definition of the Planetary Fourier Spectrometer (PFS): an FTIR spectrometer for the Mars '96 mission

The PFS is optimized for studies for the Martian atmosphere and will be also used for investigations of the surface composition. The instrument is a dual Rotational Reflector Interferometer (RRI) and covers both the SWIR (1.25 - 4.5 micrometers ) and the MIR (5.6 - 40 micrometers ) in two channels. The Noise Equivalent Spectral Radiance (NESR) is predicted to characterize the instrument. The NESR depends of the modulation coefficient, the detectivity of the detectors, the other main parameters of the interferometer, and the spectral characteristics of filters and beamsplitters as well. The modulation coefficient takes into account both the most important deviations of the optical elements from the ideal one's and partial misalignment by mechanical tolerance's. Typically estimated values are for the Short Wavelength Channel (LWC): 2 X 10-8 W/(cm2 sr cm-1) for (sigma) equals 400 cm-1 respective. Some extreme examples of the Martian surface are given where the recording of spectra is promising due to a satisfying signal to noise ratio and some other one's where measurements will be critically.