DOF Subsea completes geophysical work for E39 bridge

12 March 2019

In September 2018 DOF Subsea Norway (DOF) was awarded a contract by Norwegian Public Roads Administration, Statens Vegvesen (SVV), to undertake a 5km2 geophysical survey in Bjørnafjord, Norway.

The purpose of the investigation was to provide background data for the engineering design of a bridge over the fjord as part of the Ferry Free E39 project. This will ultimately see the nine ferries previously forming part of the 1330km north-south road in Norway and Denmark replaced by bridges, thereby reducing the total distance by 50km and journey time by up to eight hours. Work included complementary high resolution geophysical surveys (bathymetry, shallow seismic and sidescan sonar) of an area approximately 5.5km long by 800m wide.

Rather than adopting the well-established geophysical survey techniques for such topographically challenging environments, DOF opted to execute the project using the previously untested combination of a HUGIN AUV, Chercheur, owned and operated by Canada's Ocean Floor Geophysics, and their own small survey catamaran, GeoCat.

A low logistics shore-based launch of the AUV, supported by the small survey vessel equipped to provide positional updates to the HUGIN, eliminated the requirement for a traditional Remotely Operated Vehicle (ROV) and associated large offshore vessel whilst still providing the high data quality required for the project. 

The AUV containers were set up at a suitable quayside location, with a storage area and processing office also established nearby. Working during daylight hours only, the data was collected in less than a week.

In addition, detailed acoustic surveys were also carried out at a number of possible anchor locations in order to identify any objects with a 0.5m diameter, or more, which could potentially obstruct anchor placement. 

Furthermore, when the AUV was not permitted to navigate between the anchors of an established fish farm situated in the survey area, Geocat's hull-mounted seismic and multibeam echo sounder systems were utlised instead.

In all, 180km of data was safely and efficiently collected with the state-of-the-art AUV survey suite which included multibeam (MBES), sub-bottom profiler, sidescan and synthetic aperture sonar. The advanced terrain following algorithms of Chercheur afforded excellent data quality even in the very rough, undulating and rocky topography, ranging from 40m to 560m water depth, with slopes exceeding 60°.

This was the second low logistics shore-based project undertaken using DOF Subsea's GeoCat and the Ocean Floor Geophysics AUV; the first being a subsea pipeline inspection in the North Sea in March 2018. 

DOF Subsea UK Ltd
Horizons House
81-83 Waterloo Quay
Aberdeen
AB11 5DE
UK
T: +44 1224 614000
F: +44 1224 614 001

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