Applied Acoustics on an Arctic Roll
Applied Acoustic Engineering’s range of sub-bottom profiling equipment has recently won critical acclaim during a number of operations in the harsh working conditions north of the Arctic Circle, firstly as part of a research study by the University of Bergen and secondly in the search for hydrocarbons beneath the seabed.
Scientists from Bergen, Norway, have been conducting studies to determine the origin of the Alpha Ridge north of Greenland which required them to obtain seismic data from the seabed underneath autonomous drifting buoys placed on multi-year ice. Personnel from the university had developed their own sparker sound source to suit their specific requirements, but needed an energy supply to operate remotely, in sub-zero temperatures, for a period of approximately 6 months, recharging itself from its own power supply.
Applied Acoustics’ technicians, in conjunction with the university, tackled this challenge by developing a novel seismic energy supply capable of firing a 4.8KJ shot using energy harnessed from the sun. A series of solar cells were incorporated into the unit to recharge the capacitor banks easily and sufficiently, creating a viable and environmentally friendly way round what could have been a major obstacle. The successful arrangement meant that with the buoy drifting at an average speed of 5km/day, the system could fire the sparker every 50m of movement.
The reflected seismic energy, received by a single hydrophone, was digitised and recorded, and sent to Bergen via the Iridium Satellite Network. This enabled the University’s scientists to monitor the operation remotely, returning to the region to retrieve the equipment at the end of the project. Three of these drifting seismic buoys are planned for further deployment in the Spring of 2009.
Elsewhere in the Polar region, Applied Acoustics’ geophysical capabilities have been put to the test in a very different way. Their 6000J Delta Sparker with CSP-S energy source have been utilised in geohazard surveys off the northern Alaskan coast to establish the presence, or not, of shallow gas, active faulting and potential hydrate zones. The Ultra High Resolution (UHR) multichannel seismic surveys utilised a 48-channel streamer at 6.25m spacing in conjunction with the multi-tip Delta Sparker array.
The deployment of the CSP-D and Delta Sparker system offered speed of mobilisation as it required only a two-man operation and a readily available single-phase generator on a vessel of opportunity rather than a cumbersome air compressor and air-gun arrangement on a dedicated platform.
The Automatic Variable Input Power (AVIP) circuitry of the CSP-S also proved important. By smoothing the input voltage to the energy source, a soft start is provided which gradually increases the power output, reducing the load on the equipment and keeping generator requirements to a minimum.
The project was mobilised in the western Alaskan port of Nome in October 2008 and in order to maximise weather conditions the survey was performed ‘single pass’ with good quality high resolution data achieved.