A new method of remote sounding of the Martian aerosols by means of spectroscopy in the 2.7 μm CO2 band

We present a new method of sounding of aerosols in the atmosphere of Mars. It is based on the remote spectroscopic measurements of the solar radiation reflected by the planet in the region of the 2.7 μm absorption band of atmospheric CO2. The band is so strong that the radiance in its center is equal to 0 for the dust-free Martian atmosphere. The presence of suspended dust results in that some fraction of solar photons is scattered back to space without reaching the surface. Thus the intensity measured in the bottom of the band differs from 0 and can be used to determine the aerosol optical depth and to estimate its vertical distribution. We formulate general requirements for the spectroscopic observations that can provide optimal sounding of the atmospheric dust on Mars. The aerosol sounding capabilities of the Planetary Fourier Spectrometer experiment for the Mars Express mission are discussed in more detail. The equations for the radiation reflected by the non-homogeneous atmosphere derived in this work in a single scattering approximation can find applications beyond the scope of the paper.