Pulsed induction sensors (particularly the Geonics EM61 Mk2) and total field magnetometers are the two primary sensors employed for detection of munitions and explosives of concern (MEC) on formerly used military properties. While these two sensors have a broadly overlapping performance envelope, each sensor has unique strengths. The EM61 is the better sensor for detection of small and nonferrous projectiles, while the magnetometer excels at detection of large, deep objects. Unfortunately, codeployment of the two sensors is normally impossible due to the active nature of pulsed electromagnetic (EM), which creates noise on any nearby magnetometer. ESTCP project MR-200208 developed the technology needed to codeploy these two sensors through the process of interleaving (sampling the magnetometer only between the EM61’s pulses when the EM61 is quiet) and deployed that technology on a vehicular platform named Vehicular Simultaneous Electromagnetic Induction (EMI) and Magnetometer System (VSEMS).
Under this project, a Man-Portable Simultaneous EMI and Magnetometer System (MSEMS) was developed. The objectives of the demonstration were 1) to validate that the new smaller, lighter interleaving electronics worked as designed; 2) to determine whether the MSEMS system constructed around that new hardware was usable for real-world Digital Geophysical Mapping (DGM); and 3) to determine the most optimal of two physical configurations.
MSEMS is a man-portable evolution of the interleaving electronics in VSEMS. The VSEMS’ interleaving electronics were too big, bulky, and power-hungry for a man-portable application and had interface requirements that were specific to the vehicular configuration. These electronics were redesigned for MSEMS. MSEMS mounts on a commercial off-the-shelf (COTS) EM61 system with its native backpack, coil, and wheels; concurrently collects magnetometer and EM61 data; and is operable by a single person.
The interleaving hardware was made smaller and lighter to enable man-portable deployment. A box with standard interfaces was developed that allows any geophysical contractor with EM61s, total field magnetometers, and Global Positioning System (GPS) equipment in inventory to connect them to the interleaving hardware and collect high-quality, concurrent magnetometer/EM61 data. Two physical configurations were developed using this hardware: 1) a configuration with an unmodified EM61 and the magnetometer four feet in front of the EM61 coil and 2) a configuration using an EM61, whose pulse repetition rate was slowed to allow the magnetometer to acquire interleaved data when placed in the middle of the EM61 coil.
The system was demonstrated at Yuma Proving Grounds (YPG), Arizona. This deployment validated the system’s ability to collect high-quality concurrent magnetometer and EM61 data at 75 Hz with the magnetometer four feet in front of the EM61 coil and supported by a third wheel, and raised sufficient questions about signal to noise in the 15 Hz magnetometer-in-the-middle mode that the project team elected not to pursue it further. Important bugs were unearthed and fixed, and feedback from experienced operators was obtained.
This configuration has since been used on several government and commercial MEC and hazardous toxic radioactive waste surveys. A patent has been granted for the method and apparatus of interleaving magnetometer data between EM61 pulses. The box containing the interleaving hardware is the basis for the magnetometer/EM data acquisition hardware in another ESTCP project. There is commercial interest from three firms in purchasing an interleaving box.