MAGNETICS

Magnetometer and Gradiometer Surveys:-

Measurements of the local magnetic field can be used to detect variations of environmental, engineering and archaeological significance.

By measuring the local magnetic field at discrete intervals within a survey area it is possible to pinpoint areas where the magnetic field is anomalous with respect to the regional average. By measuring the vertical gradient of the magnetic field the sensitivity of the technique to variation in the upper few meters of the sub-surface is increased making the method applicable for detection of ordnance and high-resolution surveys of development sites. Anomalies are often attributable to the presence of ferrous objects and changes in geology.

The local magnetic field is measured with an instrument called magnetometer. These instruments have various operational differences which affect their sensitivity and noise rejection thresholds and the type of survey for which they are suitable.
In the image to the right we are using a caesium vapour magnetometer to locate buried drums and waste on an old landfill site. Note the Differential GPS antenna behind the operator. This set-up allows us to survey a site without setting out survey lines, allows rapid data collection and very accurate positioning frequently with accuracy to better than 1m.
A magnetometer survey over a former landfill site to locate buried drums and map waste distribution

Anomalies found during processing can be represented in single profiles or upon highly detailed maps superimposed upon your CAD-based topographic survey. With our interpretation skills we can also estimate target depth and orientation.

Below is an example of the type of output we can provide following a magnetometer survey. The survey of a former landfill site was completed with a mix of magnetometry and ground conductivity. The magnetometer data have been superimposed on a topographic plan of the site.

Magnetic survey over an infilled landfill site

Applications :-

Brownfield site surveys
Mineshafts, pipelines, utilities
Foundations and pile caps
Unexploded ordnance
Storage tanks
Buried waste & landfill
Archaeology