GEOPHYSICAL FACT FILE
ELECTROMAGNETIC METHODS 2
EQUIPMENT SYSTEMS
The main electromagnetic (EM) systems used for site investigation purposes are the Geonics EM 31, EM 34-3 and EM 38. The systems work on similar principles but use different operating frequencies, providing a range of depth penetration and resolution for different applications. Low frequency EM systems are utilised for investigating subsurface ground conditions, or finding large underground cavities such as caves and mine workings. Intermediate frequency systems are more useful for locating discrete features such as sinkholes or abandoned mineshafts. High frequency systems work best on small targets such as buried tanks, drums and other metal artifacts.
PROCESSING & INTERPRETATION
The data readings are recorded on a digital data logger during sitework, for later downloading in a PC compatable format for post-survey processing and interpretation. The most commonly used interpretation procedure is contouring, which is carried out with specialist interactive software. Our experts analyse the contoured data in detail, to identify anomalous features relative to background levels. Survey results are tied in to local ground conditions and presented as plans in an engineering compatible format that is readily understandable by the client.
(C) 2008 SUBSURFACE GEOTECHNICAL