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GSI NEW EQUIPMENT
Over the past year the GSI has taken delivery of some new equipment. In this article we outline some of these.
Marine Geology and Geophysics Programme
The Geological Survey of Ireland (GSI) took delivery of a 7.4m Rigid Inflatable Boat (RIB) from Redbay Boats at the end of June 2007 for use in support of INFOMAR survey operations. INFOMAR is the successor to the Irish National Seabed Survey (INSS) and represents a second generation advanced seafloor mapping managed jointly by the GSI and the Marine Institute. The new vessel, known as the RV GEO, is propelled by a 250HP Yamaha Diesel Inboard power unit giving a top speed of 33kts and incorporates a fully enclosed wheelhouse with state of the art navigation, communications and electronics.
The arrival of the INFOMAR RIB greatly extends the program participants' capabilities, allowing easy access and rapid deployment to Irish coastal waters where the RV GEO will be used for crucial INFOMAR support operations. Ground-truthing / seabed sampling, tide-gauge deployment and wreck surveys using side-scan sonar are just some of the tasks envisioned for the new vessel.
The concept was demonstrated recently in Mulroy Bay, Co. Donegal when a team of scientists from Vancouver based Quester Tangent (QTC) and the GSI attempted a successful ground-truthing operation of LIDAR derived seabed classification, using Grab Samplers, ROV and Drop Video. LIDAR seabed classification, which seeks to divide large areas of aerially sensed seafloor into individual classes based on physical properties, is as a technique, still in its early phases of development by QTC in association with GSI.
The vibracorer consists of a six meter metal tube approximately 20cm in diameter, which contains an interior plastic pipe, or liner used to gather a core of sediment from the upper few metres of the sea bottom. The tube is set within a large support frame in order to keep it upright on the seabed. Once securely on the seafloor, the vibracorer is driven down into the substrate by a pneumatic vibra-head. This heavy vibra-head uses a combination of gravity and low amplitude, high frequency pneumatic vibrations in order to penetrate the seafloor and gather undisturbed cores of marine sediment. The low amplitudes (a few millimetres) combined with the high frequencies (3,000 – 11,000 vibrations per minute) serve to mobilise a thin layer of material on either side of the plastic core liner, which causes the sediment to behave in an almost fluid manner and allows easy penetration of the seafloor by the vibracorer.
Initial tests of the device in Galway Bay on board the R/V Celtic Explorer prior to the April 2007 INFOMAR seabed survey, produced an important dataset with cores averaging five meters in length from a range of sediment types including sand, mud and gravel. The retrieved cores represent actual sedimentary layers throughout the area, and will allow geologists and researchers to make 3D interpretative models of its shallow geological make-up. Ground-truthing or adding physical data to the INFOMAR shallow seismic (subbottom) datasets will be a major benefit of the new device. In addition, the vibracore can be used to investigate pollutant dispersion and has been used successfully in a range of applications from marine archaeology to mineral exploration. It is expected that use of the new INFOMAR vibracore rig will make a unique and invaluable contribution to the understanding of Ireland's marine resource throughout its operational life.
Furthering INFOMAR's seismic capabilities, the program has also acquired SPARKER seismic profiling instrumentation. The Geo-Spark 200 delivered by Dutch based Geo-Resources, is the latest in SPARKER technology providing high resolution (<30cm) seismic profiles of the Shallow subbottom strata. The device achieves this level of accuracy due to its multi-tip array of sparker nodes, which are evenly spaced and set in-phase producing a very strong downward projection of acoustic energy. The system which is designed to be towed on or just below the water-surface can be used in water-depths of up to 500m, easily exceeding INFOMAR operational requirements. High resolution seismic profiles of up to 300m depth can be imaged using the Geo-Spark 200 depending on the composition of the water column, sea conditions and the nature of the underlying geology.
The availability of this system to INFOMAR survey projects, will result in a clearer understanding of Irelands near-shore shallow geology and could aid in the detection of geo-hazards such as shallow gas.
FIELD PORTABLE XRF
The Niton XL700 is a portable XRF (X-ray fluorescence) analyser that allows semi-quantitative geochemical analyses to be carried out in the field. In the laboratory, the analyser is capable of fully quantitative analyses on prepared samples with detection limits of 20 – 40 ppm for metals such as Pb, As and Cu. The analyser is being used to characterize abandoned mine sites as part of the Historic Mine Sites project. In situ analysis allows for rapid identification and analysis of contaminated substrate. It has been used successfully in the field to analyse and screen mine spoil, tailings, concentrator waste and even stream sediments.
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