The magnetometer is used to detect variations in the total magnetic field of the underlying seafloor and sub-seabed geology on the basis of anomalies in the Earth’s magnetic field, caused by the presence of ferrous iron on, or below, the seafloor. Materials high in ferrous or ferric compounds may include wreck debris, pipelines, unexploded ordnance, sites of archaeological interest or volcanic rocks; presenting significant challenges to site-developers.
In recent years the company has developed various tow configurations to allow deployment of multiple magnetometers. Most recently, this has involved using the EIVA ScanFish, accommodating 4 magnetometers on a 5m fixed wing, enabling wider coverage along each survey line. The terrain-following operation mode of the Scanfish ROTV ensures a fixed height above the seabed, improving both the quality of the resultant data and efficiency of acquisition. From our 24hr 27.5m DP1 catamarans Bibby Tethra and Bibby Athena, we also have the option of deploying multiple Scanfish systems, greatly improving efficiency without comprimising data density and quality.
On our 12hr inshore vessels, we employ various methods including fixed multiple gradiometer frames, piggy-backing sensors behind side scan sonar towfish and soft tow configurations.
Our specialist processing geophysicists combine the traditional analysis techniques of “First Principle” magnetic assessment with Oasis Montaj software using the latest ‘UX’ extensions, allowing accurate localisation and analysis of UXO targets. While providing a comprehensive workflow, this systematic approach reduces the incidences of false-positive target identification. All targets are cross referenced with other datasets, including side scan sonar data.
Flown at an altitude of 3.5m above the seabed, the d'ROP and SBI combination images the sub-seabed to a depth of 5m, greater than electromagnetic (EM) techniques can achieve, with a 5m survey swath The use of the sub bottom imager allows for not just identification and positioning of buried items, but also allows for an estimation of size and orientation of any buried feature. Generating highly repeatable chirp acoustic signals, the reflected signals are detected by a 40 channel hydrophone array, processed using a combination of coherent synthetic aperture and beam forming techniques generating true 3D acoustic data volumes. SBI rendered images are used to identify acoustic anomalies, consistent with the buried objects, infrastructure, and geohazards.
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