Development over the last two decades of electromagnetic induction (EMI) sensing technology has enabled more accurate identification of unexploded ordinance (UXO) and soil properties. False alarm rates and false negative rates for modern EMI sensors have reduced the cost associated with range cleanup dramatically. However, all EMI UXO sensors continue to have at least two problems associated with safer and more cost-effective cleanup. The first problem centers around requiring a human to push or otherwise operate a sensor on the ground potentially in harm’s way rendering the data acquisition phase of remediation costly and dangerous. The second challenge involves the data interpretation side of EMI sensing. The soil conductivity generates a response that can contaminate EMI data, though in some applications ascertaining soil properties are the goal of the sensor. We developed a lightweight time domain EMI sensor aimed at UXO detection and classification suitable for flying on a UAS platform. This sensor is designed to detect larger targets at up to 2 m from the transmitter and receiver coils. Additionally, we created a time domain sensor suitable for ascertaining the conductivity and magnetic permeability of soils in the top several meters, also suitable for UAS deployment. Both sensors have balanced payloads weighing less than 12 pounds. We present the sensors as well as preliminary calibration and field data demonstrating the efficacy and potential of these sensors to render the process of acquiring UXO data and soil property data less expensive, more efficient and safer.
Detecting and locating underground metallic and non-metallic pipes and utilities remains a pressing problem for the US Department of Energy. Old and deteriorating pipes pose a public safety and environmental hazard but often can be difficult to locate due to poor mapping or broken tracing wires. Many geophysical sensing techniques have been applied to the problem, including: acoustic methods, ground penetrating radar, passive magnetic fields, and low frequency electromagnetic fields – each with its own advantages and pitfalls. This paper investigates a new technique for detecting subsurface pipes: high frequency electromagnetic induction (HFEMI) sensing. Utilizing a frequency range of 10 kHz – 15 MHz, HFEMI has been used successfully in the past for detecting and locating low-conducting subsurface targets such as improvised explosive devices (IED). In this paper, we show HFEMI can be used to induce a linear current in a target pipe which produces a secondary electromagnetic field that can be detected by an above-ground magnetic field receiver. Comparisons between numerical and experimental studies are presented for subsurface elongated conductors. The data is inverted and then validated against ground truth.
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