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Swath bathymetry along a stretch of coast near the etruscan settlement of Pyrgi, Santa Severa, Italy
These bathymetric data were produced using the interferometric side-scan sonar onboard the Haliotis Research Vessel, Operated by Genavir, for the French Oceanographic Fleet, in September 2022, during the oceanographic campaign HISOPE (l'Haliotis pour l’Imagerie Sismique d’Orbetello et Pyrgi Etrusques).
The investigated area is located in front of the prominent archeological site of Pyrgi, the etruscan harbor of Cerveteri. At the site, next to the sea, is found a series of etruscan temples, surrounded by an etruscan city largely destroyed by coastal erosion. A roman castrum dating back to the 3rd century BCE covers part of the site and is also partly eroded by the sea. Above the castrum is built a fortified medieval village as well as a large renaissance castle (Santa Severa), built over a submerged lava dome (the Massicciata reef). In 2019, foundations of an etruscan monument were discovered 150 m offhshore, over a larger reef located south of the archeological site (the Secche di Macchiatonda). The goal of this campaign was to map the seafloor along this stretch of eroded coastline, in order to determine the location of the coastline in Etruscan time, such as to better understand the geography of the site when the harbor was settled. One of the main questions is why this specific site was chosen to develop a port, despite its exposure to waves.
Acquisition took place under stormy conditions, such that only 1.5 day of acquisition was possible over the 7 days planned. Geoswath mapping was conducted under heavy swell conditions along the sandy coast, north of of the castle of Santa Severa, then in front of the sandy coast, south of the castle, and finally over the extensive Secche di Macchiatonda reef in the south.
Data were acquired by eng. Quentin Layahe, Genavir, onboard the Haliotis, piloted by Serge Garcia, and post-processed using the software Globe, developed by the IFREMER, by Dr.Gilles Brocard (Archéorient, University of Lyon 2, France) and Alessandro Conforti, research engineer at the CNR (Italian national center for research) at Orosi, Sardinia.
coastal bathymetry, geoswath, eroded coastline, archeology, geomorphology, etruria, etruscan, Pyrgi, Santa Severa, Santa Marinella
42.028102N, 41.989326S, 11.984177E, 11.929246W
Interferometric side-scan sonar of the Haliotis
A side-scan sonar builds detailed acoustic images of the seafloor.
The interferometric side-scan sonar comprises a bathymetric function. To make a side-scan sonar interferometric, the height of an echo on the bottom has to be linked to the angle of arrival by accurately measuring the phase difference of the arrival times on the various arrays stacked on either side. By using the true bearing and the slant range (obtained by other means), the position of the sounding points can be established in three dimensions.
The main advantage of an interferometric side-scan sonar over a multibeam sounder is its greater swath width in shallow water. Bathymetric measurements are, however, less accurate than those produced by a multibeam echo sounder and suffer from excessive noise at the end of the range.
The launch Haliotis is equipped with a Geoswath interferometric sonar fixed rigidly to the hull. The device functions at a frequency of 250 kHz and provides the following measurements:
Data were post-processed using "Globe (GLobal Oceanographic Bathymetry Explorer) Software." (2019) developed by Cyrille Poncelet, Gael Billant, and Marie-Paule Corre
Bathymetry along the coast of Pyrgi at 50 cm resolution, projection system WGS 84, UTM zone 32 N (format GeoTIFF)
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10 cm -resolution bathymetry of the Secche di Macchiatonda reef, projection system WGS 84, UTM zone 32 N (format GeoTIFF)
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