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New Universities' High-Resolution Geophysical Equipment Pool

As a result of a successful bid to the higher education funding councils for Wales and England through the Joint Research Equipment Initiative, a consortium of UK Universities have acquired a suite of geophysical equipment designed for surveying the detailed surface and sub-surface structure in shallow water. Neil Mitchell from the Department of Earth Sciences at Cardiff University outlines how the equipment will be put to use.

Consortium representatives, from left to right: Tim Henstock (Southampton Oceanography Centre), Jenny Collier (Imperial College), Neil Mitchell (Cardiff University), Davie Firth (Reson), Thierry Schmitt (Cardiff University), Mark Laurence (St Andrews University), John Fraser (Reson) and Lisa McNiell (Southampton Oceanography Centre).

UK marine geophysics this year is smiling with the award of £0.5M to fund a suite of high-resolution seabed imaging equipment consisting of portable multibeam echo-sounders, Chirp sediment profiler, sidescan sonar and boomer system. The equipment pool has been acquired and is operated by a consortium comprising the universities of Cardiff, Imperial College, Southampton, Leeds and Durham.
Imaging shallow- to moderate-water depth environments and monitoring variations in their morphology and character has become an exciting new research field for the marine geoscience community. Innovations in marine acoustic technology enable us for the first time to accurately survey and quantify the morphology of sea-, river- and lake- beds. Such capability permits short- and long-term monitoring of environmental change, which has application to a range of scientific problems, societal issues and economic interests.

As a result of a successful bid to the higher education funding councils for Wales and England through the Joint Research Equipment Initiative, a consortium of UK Universities have acquired a suite of geophysical equipment designed for surveying the detailed surface and sub-surface structure in shallow water. The award was provided by the HEFCW and HEFCE, and backed by the consortium universities and by the NERC Challenger Division of the SOC. The consortium was formed to build a capability that can address issues across a broad range of academic disciplines encompassing earth, environment, geohazards, coastal engineering and archaeological research.

To address these diverse objectives, the suite of acoustic tools is designed to image the seabed and its subsurface over a wide range of water depths and depths of penetration into sediment and with a range of resolutions. We will be able to obtain bathymetric data in combination with backscatter intensity to provide geological and biological information about the seafloor, e.g., sediment bedforms, geological structures, and benthic fauna. In addition, we will be able to image the seismic structure beneath the seafloor, which will document the evolution of processes responsible for moulding the seafloor, for example sea-level changes. To aid ease of use, the equipment can be air-freighted to vessels of opportunity world-wide.

The equipment suite consists of two high-resolution Reson SeaBat portable multibeam echo-sounders (SeaBat 8101 and 8160 with TSS POS/MV inertial motion sensor), a GeoAcoustics dual frequency sidescan sonar and Chirp sediment profiler, and a boomer with multichannel streamer and recording system. The multibeam sonars together can survey over 1-3000 m range of depths and are the first such high-resolution portable systems to become available to UK academia (Figure 1). The high-frequency sidescan can be co-operated with the chirp subbottom profiler to give co-registered data. The boomer recorder system is designed to allow seismic industry techniques to be applied to high-resolution data.

Figure 1. The deeper water multibeam sonar array installed on a small tug in Cardiff Bay.

Science projects underway and planned
The original equipment proposal was based on a wide range of science, engineering and archaeology. Following initial trials with the multibeam sonars last summer, a project was started studying the morphology of tidal sand banks and their interaction with headlands. The surveyed area covers the Gower coastline (Figure 2) where there is a public perception that commercial dredging for aggregates is affecting sands on the South Gower beaches. There has been very little independent research done in this area and the public debate of the erosion issue is poorly informed, so this initial project is intended to contribute a scientific study.

Figure 2. First results from the high-resolution multibeam sonar showing sand waves off the Gower coastline (image courtesy of Mr Thierry Schmitt, Cardiff University).

This March the high-resolution sidescan sonar was used to image the site of an artificial reef about to be built in Loch Linnhe. The aim of the project is to investigate the feasibility of using artificial reefs as tools in fishery protection and enhancement for fishing communities on the west coast of Scotland. Following a successful pilot study, the plan now is to deploy 1,250,000 concrete blocks, which will make it one of the largest of its type in the world. Repeat sidescan sonar surveys throughout the reefs development will compliment the extensive biological and sedimentological surveys.

Later this year it is hoped to use the whole suite of tools to study ancient river valleys off the south coast of England that flooded at the end of the last ice age. Our aim is to determine the morphology of the valley systems in order to reconstruct their evolution in response to Late Quaternary sea-level changes. The project has application to predicting the distribution of offshore gravels, which is of commercial interest to aggregate extraction companies. The project is also of great interest for archaeologists and palaeoanthropologists, because it seems likely that these submerged river valleys formed favoured routes for migration of Paleolithic man into the UK from the European mainland. Our surveys will enable identification of potential sites of submerged archaeological resources that will contribute to our understanding of the patterns of hominid colonisation of southern England.
Deep-water mapping of volcanic islands, such as the Canaries, has revealed some huge landslides. These giant landslides are infrequent, however, occurring once every 100,000 years, so they are probably not a major threat to island populations. It is suspected that smaller landslides around the coasts of volcanic islands are much more frequent and hazardous, so the equipment is intended to be used to image and study island coastal areas. The first experiment of this type is likely to happen around the Azores.

Next year the equipment will be deployed in the Gulf of Corinth (Greece) to image seismogenic faults within the basin (Figure 3). Movement on these faults has caused some catastrophic earthquakes during historical and ancient historical times. It is hoped that the new information from these systems will help to understand the earthquake cycle there and so help the local population develop schemes to reduce their exposure to the earthquake hazards.

Figure 3. Tectonic map of the Gulf of Corinth continental rift indicating positions of major faults to be surveyed.

Additional information
Although the equipment is primarily intended for the research groups comprising the pool consortium, requests to use the equipment from other academic, government or commercial groups are welcome. For more information, please visit the website http://www.ocean.cf.ac.uk/people/neil/jrei/index.html.

Members of Consortium
Cardiff University, Dept of Earth Sciences, Dr. Neil Mitchell
Imperial College, Dept. of Earth Science & Engineering, Dr. Jenny Collier, Dr. Sanjeev Gupta
Southampton University, School of Ocean & Earth Science, Dr. Tim Henstock, Dr. Lisa McNeill
Durham University, Dept. of Geological Sciences, Prof. Roger Searle
Leeds University, School Of Earth Science, Dr. Richard Collier

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