"ARCHEOEGADI": A GIS for the Marine Archaeological Survey in the Egadi Islands

Roberto Ialuna , Daniele Gravili

CEOM S.C.p.A. (Centro Oceanologico Mediterraneo) - Gruppo ENI, Palermo (IT)

Marine archaeological surveys have usually been carried out with traditional methodology, using direct observation from divers in shallow waters or mini-submarines (AUV/ROV) in deep waters.
More recently it has become common the use of equipment derived from geophysical surveys for scientific purposes, and above all, in the offshore operation (e.g. laying and installation of submarine pipelines). Moreover, GIS tools are starting to be used for their essential role in planning and managing purposes.
Which is the goal using this kind of equipment? Firstly because the main part of the archaeological world heritage is under the sea bottom. It means that the environment can create an obstacle to the direct target vision. In addition such instrumentation provides to cover very large areas in a short time and to be able to operate in deep waters, avoiding the use of submarines. In this way we can obtain a reduction of management costs compared to surveys realised with traditional visual methods only. However the use of visual inspection methods remains always indispensable, but addressed to spot checks of suspected targets only.
The most important step in successfully locating an archaeological target is the definition of the search box, the target area where it's most likely to be found. Establishment of a target area needs the aggregation and comparison of information from multiple sources.
In this context the use of a GIS permits, e.g., the control of the navigation, to verify the acquired data-set and the checking for the coverage of the whole searching area. Moreover it also provides to aggregate, analyse and compare data allowing to improve the confidence level in identifying archaeological targets and planning fast visual inspections.
An example in using such "non conventional" equipment and GIS system for archaeological surveys has been realised in the context of an agreement between the Cultural and Environmental Sicilian Regional Authority and CEOM (CEntro Oceanologico Mediterraneo). A Feasibility Study entitled " Research and recovering project of the archaeological heritage to realise marine archaeological routes in the Western Sicily" has been developed.
Along June 2000 to March 2001, the "ArcheoEgadi" campaign took place in the marine area of Egadi Islands (western coast of Sicily). This site was the main scene of a naval battle between Romans and Phoenicians and well placed to be an important centre for the trading routes in the Mediterranean Sea. CEOM provided the co-operation of his geophysicists and engineers with geophysics and magnetometric equipment and with the support of GIS tools while S.C.R.A.S. (Servizio per il Coordinamento delle Ricerche Archeologiche Sottomarine of Sicilian Regional Authority) operated visual inspections.

Once defined the searching areas, the characteristics of the seafloor have been surveyed using:

• a Datasonics Chirp SIS 1000 (Side Scan Sonar and Sub Bottom Profiler) for geomorphologic relieves, which provides the bottom morphology and stratigraphy for the identification of archaeological objects hidden by layers of silt and clay sediments;
• a Simrad EM 3000 (Multibeam Echosounder) for bathymetric relieves to realise high resolution images of archeologically relevant sites;
• a Geometrics G-881, a differential gradiometer for differential magnetometric relieves to identify masses with mineralogical and geological characteristics different when compared with those of the surrounding sediments.

The GIS "ArcheoEgadi" performed to manage, analyse and present the geographic and descriptive data acquired during bathymetric and geomorphologic surveys was made up using the ESRI's geographic information system software ArcView 3.2a. The Arcview programming language Avenue and the Dialog Designer extension were used to personalise the user interface. The spatial analyse was performed with the ArcView Spatial Analyst and 3D Analyst extensions. Finally, the database Oracle 8 was used to manage the descriptive information acquired during the project (in particular historic and bibliographic information).
Main results achieved in "ArcheoEgadi" were a detailed map of the sea bottom to verify the application of these technologies in the archaeological field and a setup of parameters to detect the archaeological sites hidden by sediments and marine flora on the sea bottom. In particular a relevant result was the discovery of the wreck of a XI century Arabic vessel probably sank on the close to the Bull's Shoal during a storm. The wreck is about 25 m length and 5 m large, it is in a very good state and is located at about 70 meters of water depth.