Oral Session 4

A semi-analytic chlorophyll-a algorithm for sediment-rich waters

A remaining challenge for satellite remote sensing in sediment-rich estuarine and coastal waters is to distinguish the signal of chlorophyll-a from that of non-algal particles (NAP). This is the case of the Río de la Plata, a relevant estuary in South America, with turbidity levels ranging in three orders of magnitude. Previous works have shown that chlorophyll-a estimations based on band-relations do not work well for the region, while inversion models are difficult to implement due to a lack of knowledge of inherent optical properties (IOPs) in the estuary, especially for particulate matter, which highly contributes to the reflectance spectra, and could present environmental variability (i.e., due to river discharge). In this work we developed a semi-analytic chlorophyll-a algorithm that considers the contribution of NAP to water reflectance based on typical parameterizations of its IOPs, which are considered turbidity-specific. Another main difference with previous approaches is that the algorithm allows NAP absorption to be non-negligible in the red edge-near infrared region, which is typically the case for sediment-rich waters. The algorithm does not assume correlation between optically active constituents, and CDOM absorption is also estimated. The algorithm was first tested with in-situ radiometric and simultaneous chlorophyll-a measurements collected in different regions of the estuary, considering current (e.g., Sentinel-2, Sentinel 3) and future (e.g., Sabia-Mar) satellite missions. Finally, it was validated for current satellite missions using chlorophyll-a measurements obtained from different sources. In both assessments, results are better than that of previous algorithms, improving the sensitivity for concentrations below 10 ug/L.

Fernanda Maciel, Instituto de Mecánica de los Fluidos e Ingeniería Ambiental (IMFIA), Facultad de Ingeniería, Universidad de la República, Uraguay, https://orcid.org/0000-0003-3872-1121

Ana Dogliotti, Instituto de Astronomía y Física del Espacio (IAFE), Universidad de Buenos Aires, Argentina

Francisco Pedocchi, Instituto de Mecánica de los Fluidos e Ingeniería Ambiental (IMFIA), Facultad de Ingeniería, Universidad de la República, Uruguay

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