System approach and technology

Franck Goddio has developed a special system approach according to which every archaeological campaign is performed. The work begins with the study and critical review of archives and/or ancient texts, in order to determine and characterize probable locations of archaeological vestiges. With the help of non-intrusive cutting edge technology, such as a specially developed nuclear magnetic resonance magnetometer (NMR), multi-beam bathymetry, sidescan sonar, sub-bottom profiler and satellite positioning system (DGPS) the site is mapped. Test excavations are then performed in order to characterize specific features seen on the electronic maps.
If the data gives some positive clues the actual full archaeological excavations begin, involving specific databases, archaeological inventory, drawings, mapping, photographing, filming, photogrammetric coverage and 3-D follow-up rendering of the excavation.

In accordance with UNESCO recommendations stated through the Convention for the Protection of Underwater Cultural Heritage artefacts are usually left on site, in coordination with the concerned authorities they may be risen for their safeguard, study and conservation. Afterwards, conservation and the cataloging of findings by specialists are implemented. Analysis of findings are then performed by experts who also participate in the publication of scientific results. Finally, Franck Goddio also tries to present findings to the public through international exhibitions and media work.

A precise bathymetric or relief map of the survey area is obtained using echo sounders or nowadays the multi-beam technique. These acoustic sensors deliver continuous depth measurements along the survey lines. This information can be stitched together to create a highly accurate relief map. Multibeam echo-sounder brings a fundamental centimetric bathymetry of the bottom and can reveal flush constructions or wrecks.

NMR Magnetometer

Nuclear Magnetic Resonance (NMR) Magnetometers are the principal sensors in the surveying system. These highly sensitive instruments were developed by the French Atomic Energy Commission (CEA). Based on simultaneous proton and electron magnetic resonance (the Abragam-Overhauser effect), the NMR magnetometers measure the absolute value of the earth’s magnetic field more than one thousand times per second - with an accuracy of one fifty-millionth of its value. They are used to create highly sensitive magnetic maps of the seabed, which can provide vital clues about the location, orientation and size of potential buried archaeological features.

A full coverage of an excavation site can be achieved by taking hundreds of photographs with scales placed on the target. A visual reconnaissance computer’s program will assemble all the photographs in one single representation of the site.

If scales are put on the site in the 3 dimensions and if the pictures are systematically shot according to different angles (sometimes thousands of pictures), a program will enable a powerful computer to give a 3-D representation of the whole site. This technique can allow now to perform, in some cases, archaeological excavations without a physical grid set-up under water. The daily coverage of an excavation site will produce a 3-D follow-up of the work within centimetre accuracy.

The remote operating vehicles (ROVs) are equipped with cameras and are able to perform surveys in deepwaters. One can follow the reconnaissance of the robot in real time in front of screens like a video game.

The small submersibles Jules and Jim, which were designed for research at great depths, were used by Franck Goddio for excavations. Capable of diving to a depth of 1,000 metres and carrying one passenger and one pilot, they were fitted with a camera and powerful searchlights. The Deep Rovers were equipped with multifunctional articulate robotic arms with a pincer on one side and a suction cup on the other which made it possible to pick up objects delicately. The plastic bubble in which the passengers travel is to be able to withstand pressure of the sea and to allow a 320° panoramic view. Each dive could last up to 8 hours.

The water dredge is an underwater suction device that is used in excavation underwater to remove sediment. The light plastic dredge is supplied with water under pressure by a motor pump situated either at the surface or through a submersed electric pump as developed by Franck Goddio in 1992 during the San Diego excavation. A fine mesh screen at the mouth of the dredge serves to collect any small artefacts, which the diver may have missed.

Coring programmes are conducted to collect subsurface sedimentary layers. The samples are obtained by drilling cylindrical sections in the seafloor with aluminium tubes. The gathered material (sediments, rock fragments, botanical and faunal material, etc.) is analysed for composition, physical structures, disturbance of sections and colour and organic materials from within the cores can be used for radiocarbon dating. Cores help answer questions of cultural history timelines, gradual land subsidence, sudden substrate failure, sea level rise, climate change and thus help to improve the excavation strategy.  

After clearing a wreck a thorough study of the naval architecture of the boat is undertaken. It allows us to understand how ships or junks were built and how they operated at sea. The analysis of the naval architecture of the wrecks of junks discovered in the Philippines or of the indigenous Egyptian boats from Thonis-Heracleion is helping to overcome the lack of ancient sources about such vessels and opens up a broad range of questions about their construction and evolution over time.

In accordance with UNESCO recommendations, artefacts are usually left on site, in coordination with the concerned authorities some may be risen for their safeguard, study and conservation. The support vessel of the excavation is equipped with a hoist to raise artefacts to the surface. At first the artefacts are carefully places in nets, each individually labelled, then in plastic baskets. Heavier objects (like statues or steles) are moved by means of a special balloon or crane.

For a project a special elevator was designed, which had to be anchored at a depths of 350 metres. The large support buoy of the elevator consisted of sixty spherical buoys, each of them capable of resisting a pressure of 100 atmospheres. A metal-platform was laid on the sea-bed to support the two-ton lead counterweight needed to operate the elevator. The lead weight – in four pieces of half-ton pins – was attached to a balloon to make it weightless and placed in position by a submersible. The elevator was operated by a submersible and raised objects – like the ship’s bell - to the surface with the greatest of care.

Once an object reaches the surface, it is immediately cleaned in seawater, the date of discovery is entered on the label, and it is placed into a desalination tank. The tank is filled with 50% seawater and 50% fresh water, in order to avoid deterioration due to violent osmosis. After a couple of days it is placed in fresh water, which is continuously renewed. The salinity of the bath is constantly measured in order to determine when the object can be dried without damage. On land, a more complex desalination process is executed, using distilled water. Organic materials are kept in a damp environment on board, and are treated on land. After the desalination process, the object is described, measured and inventoried. Pottery is cleaned using microburins and scalpels to remove deposits and shells. Once the underwater sediments have been cleared, the object is carefully studied in reference to shape, texture and decoration in order to determine its date and provenance. Organic material requires swift and delicate treatment as soon as it has been recovered.

After desalination, the material is dried out slowly and excess water is gradually replaced by a resin, so that the volume of the material is maintained. Metals like bronze, silver, iron and lead corrode underwater. They are bathed in a regulated and precise system of chemical or electrochemical treatments. Conservation takes place chemically and ultrasonically. The revived objects can then, be chemically stabilized and covered with a protective layer.