Avaliação do potencial do satélite Sentinel-3/OLCI para a estimativa da qualidade da água do maior sistema de lagoas da América do Sul, Pelotas RS

Abstract

The Mirim-Patos-Mangueira coastal lagoon system offers a wide range of ecosystem services. However, the political division that crosses this system, along with its vast territorial extension, limits diagnostic and behavioral studies of the lagoons as a unified system. Therefore, this study investigates, in the first chapter, the water quality in this coastal lagoon system using images from the Sentinel-3 satellite and its Ocean and Land Colour Instrument (OLCI). Atmospheric correction algorithms were applied to the satellite images using Acolite, followed by the grouping of electromagnetic spectra and the creation of Optical Water Types (OWTs) with the Sentinel Application Platform (SNAP). In parallel, the Mishra and Dogliotti algorithms were applied using ACOLITE to obtain two water quality parameters: chlorophyll and turbidity, respectively. The resulting data were overlaid to analyze the correlation between the spectral grouping and the generated parameters. A pattern of increasing mean turbidity values was observed as the water types increased from 2 to 6, in addition to identifying patterns of increasing mean chlorophyll levels from class 2 to class 5, with a decrease in mean concentrations in class 6. Subsequently, a case study was conducted in Lagoa dos Patos, Rio Grande do Sul, analyzing 20 in situ samples from the Lagoa Mirim Agency (ALM) in relation to Dogliotti turbidity results, revealing an overestimation of the data, with an R² of 0.73. It was also possible to observe the lagoon's dynamics in response to floods in Rio Grande do Sul (RS) over a three-month period. In the second chapter, using the European Space Agency's (ESA) Lakes Climate Change Initiative (LakesCCI) platform, historical series of chlorophyll and turbidity from eleven tributaries of the lagoon system were analyzed. Significant trends of increasing chlorophyll were found in six of the tributaries, and significant trends of decreasing turbidity in seven of them. A more detailed study of the Camaquã tributary did not reveal any relationship between basin precipitation data and the turbidity data obtained.