Detection and especially discrimination of buried unexploded ordnance (UXO) from metallic clutter is a persistent, expensive, and pressing problem. While it is not yet clear whether or which other technologies might be best used in conjunction with electromagnetic induction (EMI) for UXO discrimination, it is clear that EMI is currently a front runner in the development of new, more effective approaches.
The objective of this project was to develop a vector (multi-axis) handheld ultra-wideband (UWB) EMI sensor and supporting data processing software and models for close interrogation of anomalies to allow a higher level of UXO discrimination in the vicinity of a noteworthy magnetic response.
This project built on the SERDP Exploratory Development (SEED) project MR-1353. The EMI sensor, GEM-3D+, design includes frequency domain vector receivers and a “beacon” positioning system. The signal processing is based on high-fidelity, physically complete forward modeling with the Standardized Excitation Approach (SEA), rigorous instrument characterization, and on advanced processing techniques such as magnetic field pattern matching, general inversion for equivalent magnetic charge capacity, optimization by Differential Evolution, and classification with Support Vector Machines.
The GEM-3D+ was constructed along with a positioning system with subcentimeter accuracy at a range of about 2 meters. This instrument has been successfully used to acquire data both under laboratory conditions and in test plots with emplaced targets. Results from all blind tests indicate the GEM-3D+ can acquire diverse and accurate vector data with a signal to noise ratio (SNR) similar to or better than prior GEM models. Single target inversion results for laboratory blind tests were 100 percent accurate. Blind tests from the test plots, with either one or two targets in close proximity, were also encouraging though less accurate. A “beacon” positioning system, which uses the primary field of the GEM-3D+ itself to locate the sensor head, was developed and successfully deployed. Early ground and stiffness sensitivities were overcome with limited redesigning of the main sensor head. The GEM-3D+ successfully acquires three axis data of the secondary field near the center of the instrument head while remaining portable for operators.
In addition to the hardware advances made during this project, the accompanying software and models are of note. The Normalized Surface Magnetic Charge (NSMS) and Standardized Excitations Approach (SEA) models were advanced and adapted for the GEM-3D+. A method to extract an absolute scale which translates GEM-3D+ ppm into physical quantities (Amps/meter) was also derived.
The GEM-3D+ is an EMI instrument capable of vector sensing of magnetic anomalies while being well located within a limited range. For cued interrogation of anomalies, the GEM-3D+ provides frequency domain data of the secondary EMI field suitable for inversion and discrimination with high fidelity, rigorous models.