Water vapor vertical distribution on Mars during perihelion season of MY 34 and MY 35 with ExoMars-TGO/NOMAD observations [Dataset]

1. Description of methods used for collection/generation of data:<br> NOMAD SO channel acquires transmittance spectra at different diffraction orders sounding the limb of the Martian atmosphere in solar occultation. It uses an echelle grating with a density of ∼4 lines/mm in a litrow configuration. An Acousto-Optical Tunable Filter (AOTF) is used to select different spectral windows (with a width that varies from 20 to 35 cm−1). Each window corresponds to the desired diffraction order to be used during the atmospheric scan. The spectral resolution of the SO channel is λ/∆λ=20,000.<br> After spectral calibration, the inversion problem is solved by fitting the data with a forward model and the vertical profiles are obtained. 2. Methods for processing the data:<br> For the H2O inversion we use the Retrieval Control Program (RCP) developed at Institut für Meteoriologie und Klimaforschung (IMK), which incorporates the Karlsruhe Optimized and Precise Radiative transfer Algorithm (KOPRA) forward model. After providing an a priori, a first-guess and the measured spectra, RCP solves the inversion problem iteratively until the convergence of the solution. The IMK-IAA level-2 processor relies on multi-parameter non-linear least squares fitting of measured and modeled spectra (von Clarmann et al., 2003). Further information about RCP and the inversion problem can be found in (Jurado Navarro et al., 2016).<br> Retrievals of NOMAD diffraction orders 134 (3011-3035 cm−1) and 168 (3775-3805 cm−1) have been obtained and merged when collocated.