The objectives of these demonstrations were to determine the effectiveness of the MetalMapperTM (MetalMapper) and Time-domain Electromagnetic Multi-Sensor Towed Array Detection System 2x2 (TEMTADS) advanced Electromagnetic Induction (EMI) sensors and advanced software in performing Advanced Geophysical Classification (AGC) to minimize the number of intrusive investigations while still recovering all of the Targets of Interest (TOIs), which include Munitions and Explosives of Concern (MEC) and Industry Standard Objects (ISOs) used for blind seeding purposes. An additional objective was to assist in evaluating the feasibility of transitioning these technologies from federal research models to commercial production models.
A total of three (3) separate instruments were utilized at the various demonstrations noted above:
- Geonics EM61-MK2 (CEMR and 29 Palms),
- Naval Research Laboratory (NRL) TEMTADS (CEMR, 29 Palms, CCR), and
- Geometrics MetalMapper (CEMR, 29 Palms).
All three instruments are time-domain, EMI sensors. Each of the sensors transmits a current through an electrical loop, which induces a primary magnetic field that magnetizes buried (or surface) objects. Turning off the transmit current causes an abrupt change in the magnetic field, which in turn excites eddy currents within the metallic object. These eddy currents then decay as a function of time and are recorded at various time gate measurements. While the basic operational theory of each of these instruments is essentially the same, the size and number of transmitters and receiver coils, as well as time gate measurements, all vary from instrument to instrument. Each of these instruments can be utilized in either dynamic mode, but only the MetalMapper and TEMTADS can be used in cued, or static, mode. The position of each is controlled using a Real-Time Kinematic (RTK) precision Differential Global Positioning System (DGPS) with sub-decimeter accuracy.
These site demonstrations showed that both the MetalMapper and TEMTADS, used in conjunction with the Geosoft Oasis Montaj’s UX-Analyze Advanced software module, were effective in distinguishing TOI from non-TOI, which include munitions debris and other debris, thus reducing the number of potential intrusive investigations. Additionally, each subsequent site demonstration revealed improvements in each advanced sensor, each leading closer to the feasibility of commercial production of said sensors.
To facilitate industry-wide implementation of AGC technology, three key factors need to be addressed: cost, mobility, and reliability. Implementation issues encountered during this demonstration include: 1) the inability of the MetalMapper to efficiently work in randomized grids during a remedial investigation, 2) the MetalMapper tow vehicle digging into unconsolidated sand when turning within a production area, which could have represented an explosive safety hazard, 3) the low height of the TEMTADS, which got caught on short corn stalks sticking out of the ground during dynamic data collection, and 4) the non-repeatable background data at CCR, which decreased the efficiently of the AGC process.