Recalibration of the relevant productivity frontal features to fish production from the MODIS-Aqua to Sentinel 3 OLCI ocean colour sensors

Phytoplankton is at the base of the marine food web but only 10 to 20 % of the primary production is available to higher trophic levels. Besides chlorophyll-a concentration, chlorophyll-a horizontal gradients were shown to mostly sustain the development of mesozooplankton and the marine food web. The detection of chlorophyll-a gradients from satellite ocean colour data therefore appears to be central to the management of sustainable fisheries.

An algorithm allowing the detection of relevant frontal productivity to fish production has been published in 2021 by the Joint research Centre (JRC). This algorithm was operationally computed and made publicly available at global scale in the JRC Data Catalogue and distributed to national institutes in Africa throughout a software named eStation within the GMES & Africa Program. This algorithm has been developed based on MODIS-Aqua data as this sensor longevity of more than 20 years is an asset for studying the temporal evolution of fish ecological habitat and the impact of fisheries by comparing effective with potential fishing yields. However, MODIS-Aqua observation will likely end soon. It becomes therefore primordial to adapt the analysis from MODIS-Aqua to the recent Sentinel 3 OLCI (Ocean and Land Colour Imager) sensor to ensure the continuity of the fish production monitoring including in real-time. OLCI-S3A, which started in April 2016, is the first sensor of the constellation to observe the chlorophyll-a concentration with the objectives to improve the daily coverage of the ocean surface and increase the accuracy of the gradient retrieval.

Here, we present the methodology used to recalibrate the relevant chlorophyll-a gradients to fish production from MODIS-Aqua to OLCI-S3A data at 4 and 1 km spatial resolution with the objective to enriching the Copernicus Marine Environment Monitoring Service catalogue and pursuing the operational marine activities of the eStation on Potential Fishing Zones (PFZ) within the GMES & Africa Program.