I am working with the IASI MetOp-B satellite data which provides information on intergrated methane in units of kg/m2, and I would like to convert it to ppm , i have also the information of surface temperature and pressure avalaible
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Converting vertical column density units from satellite to mixing ratios that represent atmospheric concentrations is not really advisable. While you can technically do it, the result would be highly uncertain, especially if you are attempting to infer "surface" concentrations. Assuming you are comparing to model data, it's actually more appropriate to convert your modeled atmospheric concentrations to vertical column density for comparison to the satellite retrievals. The satellite is detecting the entire column of the atmosphere, so the a priori vertical profile assumption inherently influences the vertical column density provided in the solution. Satellite retrievals have varying sensitivities depending on height, so any comparisons to model results should include applying the IASI averaging kernel to the model profile. The IASI level-2 documentation and De Wachter et al., (2017) discuss the averaging kernels in more detail. The averaging kernel essentially allows you to convert your modeled profiles into vertical columns that are directly comparable to the satellite, so that the differences in assumed atmospheric parameters do not confuse the comparison.
