## 1 Introduction
Furthermore, the Sentinel-2 satellite constellation is equipped with a Multispectral Instrument (MSI), which operates within 13 spectral bands (443-2190 nm) [13]. However, the light spectrum addressed in this work belongs to the true color composite: 490 (blue), 560 (green), and 665 (red) nm. This passive sensor measures the signal of water leaving radiance after the sun's radiation interacts with the water constituents [13]. Therefore, water masses can be classified accordingly to their components, which condition their optical properties and color. This classification was first introduced by [PERSON] and [PERSON] [14]. When chlorophyll (from the phytoplankton) is the constituent that determines the water mass characteristics, this water is classified as Case 1 water, which is typically associated to the open ocean. Case 2 water, on the other hand, encompasses coastal water mass, where the concentration of colored dissolved organic matter (CDOM) or total suspended matter (TSM) influences its optical properties and color [15]. Thus, the spectral signatures of coastal and oceanic water masses are expected to present inherent differences [10,15]. In Portugal, satellite technology has mainly been used to monitor water quality parameters. For instance, [PERSON] et al. [16] examined water quality parameters using Sentinel-2 imagery in the Sado estuary, and [PERSON] et al. [17] carried out a case study using MODIS and Landsat-7 ETM+ in the analysis of water quality indicators at the Mondego river estuary. A remote sensing approach for monitoring marine outfall dispersion patterns was carried out by [PERSON] et al. [18] and [PERSON] et al. [19]. In those studies, the Sao Jacinto sea outfall plume (Aveiro) was monitored through aerial photography from an airborne after outfall construction in 1998. Since the early 2000s, however, the local population and tourism in the north central region and Aveiro have grown, and more effluent water is being discharged into the sea. The aim of building the sea outfall was to relieve anthropogenic pressure on the Ria de Aveiro coastal lagoon, where the totality of wastewater used to be discharged. Hence, as an inherent process in coastal areas, marine outfall plumes' dispersion deserves special attention, as it can impact the economy and fisheries, alter water quality, and prevent leisure activities during bathing season [1; 11]. However, no study has reported on the sea outfall's plume dispersion using high-spatial-resolution satellite remote sensing technology in Portugal. In order to fill this gap in the literature, this work aims to (i) prove the feasibility of monitoring the Sao Jacinto outfall turbid plume through high-resolution S2 imagery, (ii) map the areas most frequently affected by the turbid plume, (iii) identify a pattern in the sea outfall plume's dispersal behavior through qualitative analysis of the ocean color, and (iv) understand the influence of meteo-oceanographic conditions on the outfall turbid plume's visibility and dispersion. Therefore, this paper describes the methodology used in this study for monitoring the Sao Jacinto sea outfall turbid plume with high-resolution ocean color imagery over four years, the results obtained for annual and seasonal analyses, as well as the respective discussion, conclusions, and suggestions for future work.