The Optical Definition of the Planetary Fourier Spectrometer (PFS) an FTIR-Spectrometer for the MARS'96 Mission

Abstract

The PFS is optimised for studies of the Martian atmosphere and will be also used for investigations of the surface composition. The instrument is a dual Rotation Reflector Interfermeter (RRI) and covers both the SWIR (1.24 -4.4 m) and the MIR (5.6 - 40 m) in two channels. The Noise Equivalent Spectral Radiance (NESR) is predicted to characterise the instrument. The NESR depends of the modulation coefficent, the detectivity of the detectors, the other main parameters of the interferometer, and the spectral characteristics of filters and beamsplitters as well. The modulationcoefficient takes into account both the 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 (SWC): 3*10^-10 W/(cm sr cm^-1) for sigma &#61 2500 cm^-1 and for the Long Wavelength Channel (LWC): 2*10^-8 W/(cm sr cm^-1) for sigma &#61 400 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.