Maestria

Maestría en Ciencias del Mar (2020) . Facultad de Ciencias de la Universidad de Lisboa. Directoras: Dra. C. Sá y Dra. A. I. Dogliotti

Suspended particulate matter (SPM) is one of the main water constituents in estuaries and along with turbidity (T), which is highly correlated with SPM concentration, are key parameters to evaluate water quality. Through light absorption and scattering, the SPM concentration reduces the penetration of solar irradiance within the water column and limits the photosynthetically available radiation (PAR) for primary producers and, regarding water quality monitoring, turbidity is listed as a mandatory parameter to be measured by EU member states in the Marine Strategy Framework Directive. Therefore, the quantification of these two parameters, the geographical distribution and their relationship are of crucial interest for ecosystems studies and to understand different processes such as sediment transport, primary production and the functioning of benthic communities.

This thesis focuses on the test of different algorithms with global applicability for SPM and turbidity retrieval, as well as different atmospheric corrections. The main aim of the present work is to determine the most appropriate processing scheme to retrieve SPM and turbidity for Portuguese transitional and inland waters and to determine the accuracy of retrieval algorithms with global applicability (Nechad et. al, 2009 for SPM retrieval and Dogliotti et. al., 2015 for turbidity) outside their calibration region. Sentinel-2 (MSI) and Sentinel-3 (OLCI) imagery have been used for this purpose.

For this aim, Tagus and Sado estuary, and five small water reservoirs in the Alentejo region in Portugal have been used as case-studies to test satellite imagery capability to monitor SPM and turbidity products. The in situ database has been carried out within the context of different projects (PLATAGUS, NIPOGES, Valor Sul, AQUASado, GAMEFISH) from July 2017 to July 2019 depending on the project.

In the Tagus estuary, in situ radiometric measurements conducted within the context of the PLATAGUS project allowed also to directly test different atmospheric corrections processors. These are Acolite (S2-MSI), C2RCC (S2-MSI and S3-OLCI), L2 standard MSI (Sen2Cor), L2 standard OLCI (BAC/BPAC) and Polymer (S2-MSI and S3-OLCI). Being Polymer and C2RCC the best performing algorithms for S2-MSI, while no definite results was found for S3-OLCI given the low number available data.

Results suggested that turbidity product is easier to retrieve with smaller uncertainties associated. Regarding the SPM retrieval from S2-MSI and S3-OLCI data, the associated correlations and errors indicate that there is still a strong need of algorithms development perhaps with a regional calibration specific for the optical characteristics of the study areas or finding a local relationship between SPM and turbidity as has been previously suggested. Moreover, the S3-OLCI sensor, which gave satisfactory results for the Tagus estuary, showed discordant results for the Sado estuary suggesting a poor suitability of the OLCI spatial resolution for smaller estuaries