Radiative transfer modeling with BGC-Argo float data in the Mediterranean Sea

A radiative transfer model was parameterized and validated using Biogeochemical Argo float data acquired between 2012 and 2017 across the Mediterranean Sea. Fluorescence-derived chlorophyll urn:x-wiley:21699275:media:jgrc24745:jgrc24745-math-0001 concentration, particulate optical backscattering at 700 nm, and fluorescence of chromophoric dissolved organic matter (CDOM) were used to parametrize the light absorption and scattering coefficients of the optically significant water constituents (such as pure water, non-algal particles, CDOM, and phytoplankton). The model was validated with in situ downwelling irradiance profiles and apparent optical properties derived both from irradiance profiles and satellite data, such as the diffuse attenuation coefficients and remote sensing reflectance. Results showed that by using regional parameterizations that are not only related to chlorophyll concentration and vertical distribution, the model was able to capture a more accurate spectral response in the examined wavelength range compared to chlorophyll-related (or Case 1) optical models. When using alternative models that incorporated also measurements of CDOM fluorescence or particulate optical backscattering, the model skill increased at all examined wavelengths. Finally, using a multi-spectral optical configuration also enabled the estimation of the relative contribution of separate water constituents in the examined spectral range. Simulations including non-algal particles and CDOM performed up to 61% and 79% better than when considering the optical properties of pure seawater alone. Moreover, a simulation including phytoplankton light absorption resulted in an error reduction of up to 42%, especially at 412 nm and with a more uniform response at the wavelengths considered.This work was performed within the framework of the BIOPTIMOD CMEMS Service Evolution project. CMEMS is implemented by Mercator Ocean International within the framework of a delegation agreement with the European Union. This study was supported by the following research projects funding BGC-Argo floats: NAOS (funded by the Agence Nationale de la Recherche in the frame of the French “Equipement d’avenir” program, grant agreement ANR J11R107-F), remOcean (funded by the ,European Research Council grant agreement 246777), Argo-Italy (funded by the Italian Ministry of Education, University and Research), and the French Bio-Argo program (Bio-Argo France; funded by CNES-TOSCA, LEFE Cyber, and GMMC). The authors would especially like to thank Giorgio Bolzon for his invaluable help and IT support in data management, as well as development of codes and libraries to analyze float and satellite products. Special thanks also to Ilya Chernov (Russian Academy of Science) for his contribution in developing the RT model.Peer ReviewedPostprint (published version