Page 34: of Marine Technology Magazine (October 2010)

Off the coast of the Dunwich in

Suffolk lies half a medieval town long since abandoned to the encroaching sea. Despite many diver and sonar surveys, the extent and detail of the well-known site are still unknown as poor visibility frus- trates its study. In June 2010, acoustic imaging technology was introduced to archaeological survey of the site, revealing news detail.

The site of the sunken town of

Dunwich has been the subject of debate for several centuries and the question of how much of the ancient capital of East Anglia remains just off the coast has been the subject of countless diving and archaeology projects. Since the 1300’s, historic buildings have been lost to the relentless encroachment of the North Sea but attempts to gain any detailed view of what lies beneath the water, the silt and the sand off the coast have been frus- trated by the poor visibility near the seabed. Tidal and wave currents keep fine sediments from the seabed in suspension, causing the poor vis- ibility within lower meters of the seawater that limits diving and hampers archaeological survey.

In June 2010, a team working with the BBC and MacArtney

Underwater Technology employed technology to examine the site.

Marine Archaeology Professor,

David Sear, based at the University of Southampton’s School of

Geography teamed with divers including Andy Rose from the div- ing instructor company, Learn

Scuba, and enlisted the help of sonar imaging expert, Mike

Sawkins from the MacArtney

Underwater Technology Group.

They deployed a special sonar cam- era, the diver held (or DH) DID-

SON. Each diver clipped onto a shot line which had been previously positioned over the ruins using GPS navigation and side scan sonar data.

The divers could then undertake circular sweeps of the sea bed around the shot line, gradually increasing their radius. A set of data was taken hanging over the ruins at a distance of between 8-15m, and the second set for close up visualisa- tion at 1-5m within the ruins. The combination of high frequencies, acoustic lenses and very narrow beams increased the image detail and gave archaeologists greater detail of the site than ever before available: The DIDSON diver held system enabled us to see for the first time the worked and rubble mason- ry on the seabed from the ruins of

St Katherines Chapel and St

Nicholas Church lost to the sea in c.1550 and 1480 respectively. This ability starts to open up the options for marine archaeology in near shore shallow turbid waters around coasts,” explained Professor Sear from the University of

Southampton’s School of

Geography. 3D Real-Time

Gates of the dry dock in the port of Marseille, France. Data cap- tured in real time by the Coda

Echoscope 3D Real Time Sonar.

A 3D sonar technology of the

Coda Echoscope is set for new decommissioning projects in the

North Sea and the Gulf of Mexico.

The benefits of the Echoscope’s 3D capabilities, which bring real-time visualization to the underwater working environment, were sub- stantiated in a successful role in a recent ‘plug and abandonment’ task in the Gulf of Mexico, under- lining its suitability for entry into the decommissioning arena.

Echoscope technology generates a real-time 3D image from one acoustic transmission, or ping, and from a single ping over 16,000 range and bearing points are gener- ated. The total viewing angle meas- ures 50° x 50° and within this acoustic volume, an instantaneous 3D image is generated.

Commercial achievements with

Echoscope technology have been documented in a range of diverse applications including ROV opera- tions where, as an intuitive aid to the ROV pilot, real-time 3D visu- alization augmented his spatial awareness when navigating through complex structures.

Other projects include offshore wind farm installation and under- water breakwater construction; in all cases improvements in opera- tional efficiency are reported. 34 MTR October 2010 (CodaOctopus Pr oducts Ltd.)

DIDSON Does It

Acoustic Imaging Reveals ‘Lost Town’ Detail

Television presenter and historian,

Dan Snow, (left) and Mike Sawkins from MacArtney (right) with the DH

DIDSON system.