RV Colonel Templer Cruises 01 & 02/98, 22 Apr-18 Jun 1998. TOBI surveys of the continental slope north and west of Scotland

• Main Authors: Masson, D.G., Jacobs, C.L.
• Format: Report
• Language: English
• Published: Southampton Oceanography Centre 1999
• Subjects: Norwegian Sea; North Atlantic
• Online Access: http://nora.nerc.ac.uk/id/eprint/108186/; https://nora.nerc.ac.uk/id/eprint/108186/2/SOC_CR_22.pdf

The objective of the cruise was to undertake comprehensive TOBI 30 kHz sidescan sonar and 7.5 kHz profiler surveys of several blocks of seafloor to the north and west of the UK which were released for hydrocarbon exploration in 1997 (Fig. 1). All of the license areas with water depth >200 m was to be surveyed. Surface towed 3.5 kHz high resolution profiles were also to be collected along all survey lines. The Research Vessel Colonel Templer was chartered by Geotek Ltd. to undertake the survey work. Although TOBI has a nominal swath width of 6 km, survey lines were typically spaced 4 to 5 km apart to allow for overlap between adjacent swaths, and for some reduction in range in the shallower water areas (typically < 1000 m waterdepth) in the northern survey blocks. This range reduction occurs because of severe temperature stratification in the water column, where warm North Atlantic Water (typically 8-9°C) immediately overlies cold water originating in the Norwegian Sea (typically < 0°C), causing refraction and reflection of the sonar energy. Processing of data and interpretation of results It was planned that a preliminary interpretation of the data would be undertaken during the survey, so that results could be transmitted to a related sampling cruise being carried out on the RRS Charles Darwin. This sampling cruise partly overlapped the sidescan surveys in time, necessitating a rapid turn round in data processing and interpretation. To this end, preliminary image processing was carried out on board, producing sidescan mosaics at a scale of 1:50,000. Sidescan and profile data were then combined into an integrated interpretation which was transmitted in digital form either to Geotek Ltd. or directly to the RRS Charles Darwin.Data annotation All data were recorded with reference to GMT and Julian day numbers. This report was originally issued as part of the AFEN 17th Round Atlantic Margins Environmental Survey data CD-ROM.