Oral Session 7

Bias compensation of photosynthetic available radiation from multispectral downwelling irradiance profiles

Photosynthetic Available Radiation (PAR) measurements at depth are much required by the oceanographic community to quantify the light availability for primary production. PAR is defined as the integral between 400 nm and 700 nm of an irradiance spectrum E_d. Precise estimations can be achieved by either purchasing a dedicated PAR sensor or by numerically integrating hyperspectral E_d. When E_d is only available at a discrete number of bands, the estimation as a numerical integral will inevitably be biased. In the framework of the ITINERIS project, we have developed an algorithm based on simple and exportable neural networks to compensate this bias, targeting applications for BioGeoChemical-Argo floats. Calibration was made using a dataset of hyperspectral irradiance measurements acquired by BGC-Argo floats in areas representative of the diversity of open ocean conditions. Exact PAR was calculated as the integral of the hyperspectral irradiance. Then, the same irradiance was resampled to three common band settings, and the respective biased PAR was calculated. Validation results against independent hyperspectral BGC-Argo profiles, fixed-depth E_d at the BOUSSOLE site and discrete depth profiles across the Mediterranean Sea, showed that the bias was very much reduced across a wide PAR range, with the performance mostly determined by the availability of at least one green band.

Jaime Pitarch, National Research Council Institute of Marine Sciences (CNR ISMAR), Italy, https://orcid.org/0000-0003-0239-0033

Hervé Claustre, Laboratoire d’Océanographie de Villefranche, France

Edouard Leymarie, Laboratoire d’Océanographie de Villefranche, France

Antoine Poteau, Laboratoire d’Océanographie de Villefranche, France

Vincenzo Vellucci, Laboratoire d’Océanographie de Villefranche, France

Luca Massi, University of Florence, Department of Biology, Italy

Emanuele Organelli, National Research Council Institute of Marine Sciences (CNR ISMAR), Italy

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