Atmospheric and in-water radiative transfer model validation with BGC-Argo float data in the Mediterranean Sea

Elena Terzic1, Paolo Lazzari1, Stefano Salon2, Watson W Gregg3, Emanuele Organelli4, Fabrizio D'Ortenzio5 and Vincenzo Velluci6, (1)National Institute of Oceanography and Applied Geophysics (OGS), Trieste, Italy, (2)National Institute of Oceanography and Applied Geophysics (OGS), Oceanography, Trieste, Italy, (3)NASA Goddard Space Flight Center, Greenbelt, MD, United States, (4)Observatoire Océanologique de Villefranche, Villefranche sur Mer, France, (5)Observatoire Océanologique de Villefranche, Villefranche Sur Mer, France, (6)Observatoire Océanologique de Villefranche, Villefranche-sur-Mer, France
In order to improve our current knowledge on marine biogeochemical processes (e.g. primary productivity, chlorophyll concentration, plankton biomass and water turbidity), it is necessary to follow up with the pace of the multi- and hyperspectral approaches in remote sensing and in-situ platforms also within the modelling community. Most ecological models, despite their increasing spatial resolutions, shorter computational times and improved biological complexity, still employ an oversimplified methodology for optical calculations, usually to predict photosynthetically available light without considering its spectral dependency. A link between radiometric quantities and biogeochemical variables can be thus established with an enhanced description of in-water optical properties through their absorption and scattering fingerprints.

With that in mind, an ocean-atmosphere spectral irradiance model was adopted with the final aim of upgrading the existing light parameterization for the CMEMS Mediterranean Sea biogeochemistry component.

We hereby demonstrate the first findings of a 1-dimensional multi-spectral bio-optical model comparison with the BGC-Argo data set in the Mediterranean Sea (including 4700 profiles between 2012 and 2017) in two different ways. Firstly, in the form of a match-up of surface downwelling irradiance data from BGC-Argo floats (at three wavelengths, i.e. 380, 412 and 490 nm) versus in-water irradiance obtained with the use of the atmospheric component of the OASIM spectral irradiance model. Secondly, through an in-water three-stream radiative transfer model validation with BGC-Argo radiometric profiles. More specifically, we test different parameterizations of inherent optical properties of the major water constituents, i.e. pure water, non-algal particles, phytoplankton pigments and colored dissolved organic matter, and subsequently show the configuration that gives the highest skill when comparing modelled and measured radiometric profiles.