Evaluation of Posidonia oceanica Map Generated by Sentinel-2 Image: Gulbahce Bay Test Site

Remote Sensing offers an effective and low-cost solution for mapping the extent of seagrasses and temporally monitoring them routinely. In an in-situ well-explored Gulbahce Bay test site, we used a high-resolution Sentinel-2 image to map the distribution of P. oceanica. Atmospheric and water column corrections were applied to the raw image. Thematic maps of the area were obtained by supervised classification and their accuracy was evaluated by cross-validation. The produced maps were also compared to a previously generated high accurate thematic map generated by the combination of sub-bottom profiler, side-scan sonar, and very high-resolution satellite image data. The classification achieved nearly 88% user accuracy at best. The assessment of the accuracy was also carried out in terms of water transparency. For this purpose, Secchi disk depths (SDDs) over the study area were inverted from the satellite-derived vertical attenuation coefficients by using a model. This model was retrieved by tuning the coefficients to 22 local SDD measurements. Sentinel-2 twin-satellite with its high spatial and temporal resolution data can contribute to mapping the P. oceanica cover in shallow waters. Their multispectral data can also be utilized for deriving the water transparency in order to determine the application limitations of the generated map.