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MATMOS, GGG, and the Atmosphere of Mars

The Mars Atmospheric Trace Molecule Occultation Spectrometer (MATMOS) mission will deploy a high-resolution solar occultation infrared Fourier transform spectrometer (FTS) to Mars on-board the ExoMars Trace Gas Orbiter in 2016. The MATMOS instrument will have a spectral resolution of 0.02 cm^-1 over a wavelength range of 850 - 4300 cm^-1. MATMOS will improve detection capabilities by an order of magnitude, with projected detection limits in low-dust conditions of, for example, 4 ppt for CH4, 12 ppt for HO2, and 1 ppt for NO2, N2O, and H2O. Analysis of measured solar absorption spectra will be done with the GGG software suite, developed at JPL. This work will present the techniques that will be used by MATMOS to retrieve temperature using the CO2 nu-3 vibration-rotation ban, and to retrieve tangent altitude from pointing information and CO2 absorption lines. If these are well enough understood then we are capable of retrieving volume mixing ratio (VMR) vertical profies for several trace gases. We demonstrate its capabilities by analysing spectra measured in the Earth's atmosphere by the Atmospheric Chemistry Experiment (ACE) on SCISAT and comparing results to the retrievals done by the ACE science team. A look at the software's capability to do retrievals in a Mars-like atmosphere is under investigation using synthetic spectra created by GGG for varying dust conditions. A major challenge of studying the atmosphere of Mars is that it often contains a high amount of dust, decreasing total transmittance. Dust can produce spectrally broad extinction features, cause scattering at higher frequencies, and cause large, wavelength-dependent variations in the solar intensity during the acquisition of a single interferogram. These will distort the instrument line shape and must therefore be corrected or accounted for in the spectral analysis.