Use of echosounders in marine archaeology: survey of harbour in syracuse

Simona Raneri, Enrico Greco

YOuth in COnservation of CUltural heritage, ISBN: 978-88-86208-59-8
DOI: 10.13140/2.1.4062.7521

Over the last ten years, the high-resolution marine geophysical survey field has witnessed significant advances in survey investigation equipment. New equipment are addressed towards the use of quantitative acoustic methods for the high-resolution mapping of the seafloor for archaeological heritage management. In particular, side-scan sonar and sub-bottom profiler are been tested in Syracuse areas, especially in Porto Grande, about a project led under the supervision of the Sea Superintendence of Palermo and in collaboration with Aurora Trust, Malta, and Pharos s.a.s., Milan. Generally, these high-resolution equipment are becoming affordable for use on archeological projects thanks to the high accuracy of the measures, the high spatial resolution, the repeatability of the results, and the possibility to integrate the data with other scientific ones. In addition to this, through the use of geographic information system (GIS), quantitative results are stored in digital format for post-survey processing. The Side-Scan Sonar system is applied to survey the morphology of the seafloor. This system identifies the different types of the seafloor (such as sand, rocks, mud, Posidonia, and so on) and objects eventually dispersed on the seafloor (such as wreck). The system is based on the different backscattering given by various materials and lithotypes and it records the backscattering data through a digital technology that gives back high-resolution images. Finally, the individual side-scan strips can be joined together to obtain a side-scan mosaic of the surveyed region through SonarWizMap software. Sub-bottom profiler allows to identifying the litho-stratigraphic sequence of the seafloor and it is based on the different sound speeds through the sediments. The penetration and the reflection of the backscattering depend on the physics characteristics of the material surveyed and from signal power and frequency. The backscattering impulses are recorded by the same echosounder that transmits the signal. The system uses digital Chirp technology to create high-resolution images. On the surveyed area it’s usually realized a mesh of strips, in relation to the accuracy required. The two systems (sub-bottom profiler and side-scan sonar) can be used together to have an exact correlation of the areal and depth information.

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