A magnetometer measure variation in the earth’s magnetic field and can be used to detect anthropogenic features on the seabed, buried on land or alternatively to assist in the mapping of geological features.
Small local anomalies result from the contrasting levels of magnetic susceptibility which exist between in-filled ‘cut’ features or structures and the local substrate or bedrock.
Magnetometer surveys are used in a variety of fields, and are particularly well suited to the detection and mapping of all sizes of ferrous objects including anchors, chains, cables, pipelines, ballast and other scattered shipwreck debris, munitions (UXO), aircraft, engines and any other magnetic objects.
We have invested in the industry-leading Geometrics G-882 Cesium-Vapour Marine magnetometer, c/w altimeter, to ensure we produce reliable, high quality results when undertaking magnetometer surveys.
Where UXO detection is required, surveys are usually undertaken along pre-determined grid lines (often following desk-top analysis of historical records) with data logged at an average of four readings per metre. On-site data processing allows results to be monitored and modified as required relative to local conditions.
We have extensive experience of using magnetometer systems as part of a UXO detection surveys, providing supplementary information via both multibeam bathymetry and side-scan sonar systems.
Magnetometers are also used in a broader prospecting role to initially locate areas of ‘magnetic activity’ and to help determine the extent of anomalies associated with previously identified features. Objects as small as a screwdriver can be detected provided that the sensor is close to the seabed and within practical detection range.
Often two magnetometer sensors are mounted in a gradiometer format, which measures the magnetic gradient between two sensors arranged on a horizontal separation, normally 1m or 2m apart. Readings can be automatically logged allowing large amounts of data to be recorded and stored quite rapidly.
Post-processing is undertaken within proprietary software that allows data to be checked & verified and processed in profile form. The software reliably converts high volumes of magnetic data into modelled grids and provides target locations, depths, size and apparent weight calculations.
Surveys can be used specifically for object detection or alternatively for wide area geological analysis in order to assist in the interpretation of sub-seabed structure and morphology. Deliverables include written reports with data exported in industry-standard formats such as AutoCAD, ASCII, PDF & XYZ files.