AOTF-based spectrometer for Mars atmosphere sounding

Abstract

The SPICAM Light optical package on the ESA Mars Express mission is dedicated to the nadir, limb, solar and stellar occultation observations in the UV and NIR spectral ranges. A lightweight (~0.7 kg) near infrared channel of this instrument employs an acousto-optic tunable filter (AOTF). To our knowledge it is one of the first spectroscopic applications of the AOTF on a civilian spacecraft. A single-pixel spectrometer will sequentially measure the spectrum of reflected solar radiation from Mars between 1 and 1.7 μm with spectral resolution of 3.5 cm^-1, and spatial resolution of ~6 km from 250-km Mars Express orbit. A fiber-coupled solar entry allows profiling of the Martian atmosphere in solar occultations. A chosen configuration of the AOTF conserves both polarizations allowing therefore spectro-polarimetry measurements. The main scientific objectives of the instrument are the measurements of vapor column abundance simultaneously with ozone (measured in the UV channel) and retrieving of H₂O profiles in solar occultations. The flight model of the instrument is assembled and calibrated. Future development of the instrument including employing a multipixel linear array for cross-track mapping and extension of the spectral range is discussed.