Experience in detection of unexploded ordnance (UXO) has seen the overwhelming adoption of digital electromagnetic and magnetic sensors. Each has its advantages and disadvantages. Those seeking the highest standards of detection and remediation performance demand that both be used and only accept analytical discrimination between UXO and non-UXO targets that is defensible. Those funding UXO remediation recognize the need for a single-pass sensor system that can be used efficiently in all terrain conditions, satisfy detection standards at least equal to a combined electromagnetic and magnetic search, and deliver data from which false alarms may be minimized without compromising UXO detection. This project will demonstrate and validate a sensor technology with the potential to reduce UXO remediation costs by enhancing detection performance and delivering discrimination against false alarms that will satisfy regulators.
Sub-Audio Magnetics (SAM) is a patented method by which a total field magnetic sensor is used to simultaneously acquire both the magnetic and electromagnetic response of subsurface UXO. A wire is first laid along a "meandering loop of convenience" surrounding the area to be searched, which may be several acres in size. A time-varying current then is transmitted at a sub-audio frequency of typically 32 hertz. Total field magnetic measurements are acquired at a rate of up to 8 kilohertz while systematically traversing the area within the loop as for a conventional magnetic survey. Post-processing then separates the total magnetic field intensity and the total field electromagnetic transient response. Both are mapped to the position where the measurement was acquired using a Differential Global Positioning System or alternate positioning technology.
SAM has the potential to significantly exceed the individual detection performance (i.e., reliability and depth) of both magnetics and electromagnetics. Joint inversion of independent, co-registered response parameters will deliver discrimination capability not possible from a single detection parameter response, without compromising UXO detection. Achieving a higher probability of detection and a defensible discrimination performance from a single-pass, highly portable detector system will result in the total cost of UXO remediation being significantly reduced through improved search efficiency and a reduced rate of false alarms.