Four video tows were completed for sub-area 1 and three tows for sub-area 2. Groundtruthing data was collected for the Blackstone Bank region on 16th February 2004 by M. Service and J. Strong (QUB). Ground-truthing was limited at Stanton Banks by poor weather conditions and the size of the survey area. The video tows were undertaken from a towedsledge that was deployed from the stern of the ship. The amount of cable deployed and depth of water were noted during these surveys such that sledge layback could be calculated and the position corrected. The video system comprised of a Kongsberg Simrad Osprey underwater video camera operated using a Simrad video control deck unit and recorded on VHS tapes via a Panasonic video recorder. Positional information was imprinted on the film using a dGPSlinked to TrakView overlay system.

Videotapes were later copied to DVD using a Philips DVD Recorder. A stills camera system (Photosea 1000A 35mm camera and Photosea 1500S strobe) was also fitted to the sledge and operated through the Simrad video control unit. Slide film was used, with the resulting stills scanned onto computer using a Nikon CoolScan IV slide scanner. These images were enhanced using Adobe Photoshop, and catalogued with positional information, which was determined as far as possible using the associated video footage.

Multibeam sonar datasets were collected over two areas in Stanton Banks and in the Blackstone Bank area on 25th and 26th June 2003 respectively, using an EM2000 Multibeam Echosounder (MBES, Kongsberg Simrad Ltd; operators: J. Hancock and C. Harper). The sonar has a frequency of 200kHz and ping rate of 10Hz. It operates with 111 roll-stabilised beams per ping with a 1.5 degree beam width along-track and 2.5 degree beam width crosstrack.

The system has an angular coverage of 120 degrees. In addition to bathymetric coverage, the system has an integrated seabed imaging capability through a combination of hase and amplitude detection (referred to here as ‘backscatter’).

The EM2000 was deployed with the following ancillary parts:

• Seapath 200 – this provides real-time heading, attitude, position and velocity solutions with a 1pps timing clock for update of the sonar together with full differential corrections supplied by the IALA GPS network. The GPS derived heading is measured with a 2.5m beam, 0.075 degree RMS (root mean square).
• Motion Reference Unit - MRU5 - Roll and pitch accuracies of 0.03 degree RMS.
• Sound velocity meter - Applied Microsystems singaround velocimeter to measure sound velocity at the sonar head.

The data derived from the Seapath 200 and MRU5 were integrated within the Merlin acquisition software suit for full geo-reference solutions at each sounding (depth) location.

A number of software suites were used during the acquisition and subsequent data reduction. During the survey Merlin acquisition software was used on a Solaris UNIX workstation  Simrad Survey Systems) for acquisition and quality assurance/quality control. This recorded all the acquisition data and also applied sound velocity at the sonar head and through the water column. Roll, pitch, timing, and heading calibrations were undertaken with this software.