| Summary: | Progress Code: completed Statement: The MAX-DOAS technique relies on precise knowledge of the viewing geometry. This is an inherent challenge of MAX-DOAS measurements on a moving vessel. The Envimes MAX-DOAS instrument used in this work has in-built elevation angle compensation firmware which for slowly varying pitch/roll of the ship works well, however in rough seas this is not always the case. Recommendation for data analysis: The spectral log files contain ‘start elevation angle’ and ‘end elevation angle’ fields. This can be used to calculate a difference whose absolute value should not be greater than 0.2 for confidence in the the measured viewing geometry. Purpose This dataset comprises chiefly of solar scattered light spectra (level zero product) collected using a MAX-DOAS instrument. The MAX (Mult-Axis) refers to the fact that spectra are collected in a ‘set’ of elevation angle scans (-3, -2, -1, 0, 1, 2, 3, 5, 10, 20, 40, 90 deg). The DOAS (differential optical absorption spectroscopy) refers to the analysis method required for analysis of the scattered light spectra. Briefly, analysis of these spectra relies on fitting absorption cross sections of trace gases of interest to determine the amount of trace gas integrated along the scattered light path, for each elevation angle in each set, using an appropriate fitting algorithm. This gives the slant column density for each trace gas at each elevation angle (level one product). The differential slant column density (dSCD) is determined by taking the ratio of low elevation angle scans with zenith scans, producing tropospheric specific information. Typically some atmospheric corrections are required to be included in the analysis including a polynomial, which accounts for broadband absorption and scattering processes, and corrections for the filling in of solar Fraunhofer lines (the Ring effect). By inverting measured dSCDs, and dSCDS modelled using a radiative transfer model, vertical profile information for trace gases can be calculated using MAX-DOAS ...
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