## 3 Results
### Performances of the SRT Inversion Retrieval Process Using Synthetic Data
The retrieved Chl values range between 0.1 and 0.6 mg m\({}^{-3}\), which is highly consistent with the Level-2 \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameters** & **Retrieval for a _Sargassum_ Free Pixel** & **Retrieval for a _Sargassum_ Contaminated Pixel** \\ \hline Chl (mg m\({}^{-3}\)) & 0.41 & 0.45 \\ NAP (g m\({}^{-3}\)) & 0.243 & 0.26 \\ CDOM (m\({}^{-1}\)) & 0.025 & 0.02 \\ FC (\%) & 15 & 8 \\ z (m) & 5 & 0.07 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Retrieved values of the bio-optical parameters estimated by the SRT inversion method for a _Sargassum_-free pixel and a _Sargassum_ contaminated pixel for the OLCI data acquired on 8 July 2017.  
product values that ranges from 0.2 to 0.8 mg m\({}^{-3}\). The retrieved NAP values range between 0.4 and 1.4 g m\({}^{-3}\), which is overestimated in comparison with the Level-2 product values that ranges from 0.13 to 0.32 g m\({}^{-3}\). The retrieved CDOM values range between 0.02 and 0.05 m\({}^{-1}\), which is fairly consistent with the Level-2 product values that ranges from 0.04 to 0.06 m\({}^{-1}\). The retrieved FC values range from 0 to 47% (Figure 7d). The retrieved depth values range from 0 to 5 m (Figure 7e). The pixels of the study area for which the retrieved depth reaches 5 m are considered as _Sargassum_-free pixel as explained in Section 3.1. Their associated FC values will further be discarded. Here, the presence of _Sargassum_ can be found in areas for which z is lower than 4.9 m, typically between 15\({}^{\circ}\)30\({}^{\prime}\)N-61\({}^{\circ}\)45\({}^{\prime}\)W and 15\({}^{\circ}\)15\({}^{\prime}\)N-61\({}^{\circ}\)30\({}^{\prime}\)W (Figure 7e). Around 15\({}^{\circ}\)30\({}^{\prime}\)N and 61\({}^{\circ}\)15\({}^{\prime}\)W, FC is higher than 30%, and the related depth reaches 2.5 m. Note that such an area is influenced by the mouth of the Layout river (western Dominica Island). It is likely that the high-water turbidity induced by the river discharge leads to the failure of the model; the area is wrongly identified as _Sargassum_ dominated. Note that turbid coastal zones might be discarded by extending a land-mask to the nearby coastal waters. The retrieved FC and z values are filtered out to discard pixels corresponding to a depth higher than 4.9 m and a FC lower than 0.1% to visualize the _Sargassum_ aggregations in the study area (Figure 8). Land/ocean borders are contoured in black. The FC values range from 0.1% to 39%. The _Sargassum_ coverage of the area of interest can be estimated using the FC retrieval and the size of a OLCI pixel (0.3 \(\times\) 0.3 km). The coverage area of _Sargassum_ is then estimated to be 19.86 km\({}^{2}\) over the total 22,500 km\({}^{2}\) study area. FC tends to be higher in the center of the aggregations than on their edges (Figure 8a), which is consistent with the fact that the _Sargassum_ could be more dispersed at the edges of the aggregations due to the water mixing. About 80% of the retrieved depths are located between 1 m and the surface. The remaining 20% left is then retrieved between 1 and 4.9 m. The greater depths (z \(>\) 1 m) seem to be retrieved on the edges of the aggregations while the shallow depths (z \(<\) 1 m) are observed in the center of the aggregations (Figure 8b). This could be explained by the fact that the abundance of _Sargassum_ is lower on the edges of the aggregations, and thus the _Sargassum_ buoyancy is decreased. The retrieval of FC is also performed using the \(\delta\)MCI approach. Note that the values retrieved by such a method for which FC is lower than 0.1% were filtered out; thus, the isolated pixels are discarded to prevent false detections. The comparison between \(\delta\)MCI and SRT inversion approaches is performed using a histogram (Figure 9). The histogram shows that FC values greater than 5% have more occurrences when using the SRT inversion (in red in Figure 9) than when using the \(\delta\)MCI approach (in blue in Figure 9).