Vehicular-towed magnetometer arrays have been used for munitions and explosives of concern (MEC) detection since the late 1980s. However, most vehicles are highly ferromagnetic due to their ferrous frame, skin, and drive train, and the resulting magnetic self-signature can easily overwhelm the signal from subsurface objects and render the data useless. Further, because the vehicle signature is induced by the Earth’s magnetic field, it is not constant; it changes primarily with the vehicle’s orientation relative to north, and secondarily with the vehicle’s pitch and roll. Several successful vehicle-towed magnetometer arrays have addressed the vehicle signature problem through the use of custom-built nonferrous, aluminum-framed vehicles that minimize vehicle self-signature. However, the cost of these vehicles was in excess of $100,000, putting them out of range of commercial unexploded ordnance (UXO) contractors. The logical question is: Is this kind of expensive custom vehicle absolutely necessary to acquire high-quality towed array magnetometer data, or can a contractor employ a vehicle with a higher signature and filter out its effects?
The objectives of the demonstration were:
Under this project, the demonstrators tested a number of COTS side-by-side utility vehicles (UTV) and an all-terrain vehicle (ATV) for their applicability as tow vehicles for a towed magnetometer array by measuring their magnetic signature and determining if the signature can be removed through simple filtering techniques to yield data of a similar quality to data obtained using a custom-built vehicle.
SAIC selected what it felt was the best compromise of low signature, cargo space, terrain-handling capability, and ride—the aluminum-framed Club Car XRT 1550—purchased it, and adapted it to pull SAIC’s full-sized VSEMS mag/electromagnetic (EM) 61 towed platform (developed under ESTCP project MR-200208). The demonstrators found that this vehicle engenders only a moderate signature in the data and that this signature can be easily removed with the de-median filter in Geosoft Oasis Montaj that is already commonly employed for filtering geophysical data.
Because the sensors are not only COTS but the very sensors already well-used for MEC DGM, training is minimal. However, due to the number and variety of sources of noise (of which directionally varying magnetic signature is only one), background or experience in magnetometry is necessary to build a system that collects high-quality magnetometer data.