New comparative mapping around Lampedusa, Linosa and Lampione, Pelagie Archipelago (Sicily Channel)

In the course of three years, the CNR-ISMAR of Naples carried out the surveys ("Lampedusa 2015", "Linosa 2016" and "BioGeoLin 2017") with the aim of studying the seabed of the insular shelf of Lampedusa, Linosa and Lampione, the three islands belonging to the Pelagie Archipelago. A common feature of all three surveys was the use of the multibeam Teledyne Reson SeaBat 7125 400 kHz (Innangi et al., 2018; Innangi et al., 2019), providing sub-centimetric resolution in the bathymetric data at that depth range between 5 to 180 m. Furthermore, the vessels employed were equipped with the same auxiliary instruments, i.e. an Oministar DGPS (for position data), an IxSea Octans 3000 (for attitude data), and a Valeport mini-SVS sound velocity probe installed near the transducer (for beam steering). For all surveys, the snippet data was logged (as backscatter information) with the same Absorption and Spread acquisition parameters. Also the data processing was the same, e.g. the snippet data was processed using FMGeocoder Toolbox (FMGT) in Fledermaus 7.6 version (QPS, 2016) to produce mosaic images with the same amplitude range, from -60 dB (lighter tones, corresponding to low backscatter) to -25 dB (dark grey tones, corresponding to high backscatter). Furthermore, ground-truth information, in the form of video-investigation (for all islands) and grab samples (only for Linosa and Lampione), were collected during the surveys. These characteristics made it possible to analyse all islands with RSOBIA (Remote Sensing Object Based Image Analysis) with the integrated information derived from backscatter data and bathy-morphological features, validated by ground-truth data (Innangi et al., 2018; Innangi et al., 2019) to produce three seabed maps, including seagrass distribution and benthoscape classification (according to Lacharité et al., 2017), and comparable to each other. Finally, it must be emphasized that the maps provided the first indication of the occurrence of rhodolith and maërl habitats at Lampione and Linosa, which are among the most important ecosystems in the Mediterranean Sea, while for Lampedusa further ground-truth data are necessary to better characterize the acoustic facies pattern of the island (Innangi et al., 2018; Innangi et al., 2019)