BGS Offshore Geoindex
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Lundy, Cardigan Bay, Western Channel & Celtic Sea, Irish Sea, CELTIC SEA, IRISH SEA
publication: 2010-05-02
2010-04-17
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2010-05-02
grid
British Geological Survey (BGS)
The Lyell Centre, Research Avenue South,
Edinburgh,
EH14 4AP,
UK
tel: +44 (0)131 667 1000
email:
enquiries@bgs.ac.uk
Role: custodian
CADW
email:
offshoredata@bgs.ac.uk
Role: originator
Data Quality
Geophysical equipment types used included: Magnetometer and Sidescan Sonar. Wessex Archaeology was contracted to undertake the survey on behalf of CADW. Positions were provided using Leica 500 Trimble RTK beacon receiving corrections via satellite or a Trimble DGPS, which received differential corrections via land stations to provide a position to within 0.6m. Positions were recorded using World Geodetic System 1984 (WGS84) Datum and projected as Universal Transverse Mercator (UTM) Zone 30 North co-ordinates. The navigation data were recorded using Hypack (2008 v.2). The sidescan sonar data were acquired with a Klein 3900 towfish system. This system uses the latest technology in digital sidescan sonar imaging and can operate at either low (445kHz) or high (900kHz) frequency to provide high resolution images. The data were digitally recorded in xtf format using SonarPro Software. The sidescan sonar towfish layback values were recorded on survey logs and also applied to the raw data in SonarPro as it was recorded. The magnetic gradiometer data were acquired using Geomatrix’s G882 gradiometer system consisting of two marine caesium vapour magnetometers arranged horizontally 1.5m apart on a transverse gradiometer tow frame. The gradiometer frame was deployed independently of the sidescan sonar system, permitting the separate adjustment of fish heights. A fin and lead weight positioned under the centre of the frame were used in addition to those attached to each of the magnetometers in order to aid the submersion and stability of the gradiometer. This system was chosen for its high performance in shallow water with high sensitivity and fast sampling rate with a resolution of 0.02nT at 0.1 second sample interval and an absolute accuracy of <3nT throughout the range. The system only suffers a heading error of +/- 1nT error through a 360° arc. The gradiometer data were recorded in Geomatrix software Maglog and exported into ASCII files in real-time, where the raw and corrected position, field value, altitude and depth for each of the magnetometers were recorded in a single string. All magnetometer layback values were applied to the raw data in Maglog during recording and detailed on survey logs. In cases where the layback calculation failed the gradiometer data were corrected during the processing stages.
Minimal Distance:
5 urn:ogc:def:uom:EPSG::9001
INSPIRE Implementing rules laying down technical arrangements for the interoperability and harmonisation of unknown theme
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Metadata about metadata
c5bc60cd-04eb-3862-e044-0003ba9b0d97
British Geological Survey (BGS)
The Lyell Centre, Research Avenue South,
Edinburgh,
EH14 4AP,
UK