An object, made partly or wholly of metals, has a distinct combination of electrical conductivity, magnetic permeability, and geometrical shape and size. When the object is exposed to a low-frequency electromagnetic field, it produces a secondary magnetic field. By measuring the broadband spectrum of the secondary field, we obtain a district spectral signature that may uniquely identify the object. Based on the response spectrum, we attempt to 'fingerprint' the object. This is the basic concept of EMIS. From numerous surveys that we have conducted using our multifrequency electromagnetic sensors (GEM-2 and GEM-3), we have accumulated significant evidence that a metallic object undergoes continuous changes in response as the transmitter frequency changes. These observations made over may UXO targets suggest strongly that the EMI anomaly measured in a broad band offers an ability to both detect and identify a target. The frequency-dependent structure of the difference was also reproducible and consisting over a range of depths. Therefore, we have established that the FEM-3 is capable of delivering broadband EMI data with ample target-specific information content for the purpose of target classification and identification.
Although commercially available geophysical sensors are capable of detecting UXO at nominal burial depths, they cannot reliably discriminate between UXO and clutter. As a result, an estimated 75% of remediation funds are spent on nonproductive excavations. During the past few years, we have been studying the merits of using multifrequency EMI data for discriminating between UXO and non-UXO targets and believe the method has tremendous potential. The EMI spectral response of an object is a function of its electrical conductivity, magnetic permeability, shape, size, and orientation relative the primary exciting field. By measuring a target's spectral response, we obtain its characteristic frequency-dependent signature.
The pyrolysis of TNT and other explosive compounds generates signature compounds that can be efficiently detected by electrochemical sensors. This concept was implemented in the development and testing of a sensor probe for the Site Characterization and Analysis Penetrometer System (SCAPS) for the in situ detection of TNT, RDX, HMX, and other nitrogen-containing soil contaminants. This paper describes the results of laboratory studies and field tests conducted to determine the feasibility of employing electrochemical sensors for detecting subsurface explosives contaminants. A method for the in situ pyrolysis of explosives contaminants in soils was developed, and laboratory tests determined that electrochemical sensing of the pyrolysis products was sensitive, selective, reversible, and capable of broad dynamic range. A penetrometer probe that accommodates the electrochemical sensors (including power supply and signal conditioning electronics), the pyrolyzer unit, the pneumatic components, and geophysical sensors for soil classification was designed and fabricated. Results of tests conducted at the Louisiana Army Ammunition Plant during September 1994, which demonstrated the performance of the SCAPS sensor under actual field conditions, are presented.
A remote minefield detection system (REMIDS) developed as part of the U.S. Army's Standoff Minefield System Research Program is presented. This helicopter-mounted system based on an active/passive line scanner, real-time processing, and display and navigational equipment obtains image data in three principal coregistered channels via line scanning. Two channels provide near-IR linear polarization reflectance vector information while the third channel provides passive thermal information. Numerous flight tests showed that the REMIDS system is capable of detecting mines during both day and night flight. Polarization is confirmed to be are a good discriminator between man-made and natural objects. Active polarization and reflectance information proved to be superior to thermal data in several natural scenarios including arid regions, overcast conditions, and diurnal thermal crossover periods.
Conference Committee Involvement (3)
Detection and Remediation Technologies for Mines and Minelike Targets X
28 March 2005 | Orlando, Florida, United States
Detection and Remediation Technologies for Mines and Minelike Targets IX
12 April 2004 | Orlando, Florida, United States
Detection and Remediation Technologies for Mines and Minelike Targets VIII