Introduction to the Mine Problem

In spite of recent advances in detector technology, metal detectors, mine probes, and canines remain as the most widely utilized mine detection tools. All of these methods have been utilized with some success, but all have limitations. For example, metal detectors must be operated at extremely high gain settings to obtain adequate sensitivity to detect low-metal-content mines. This is an issue because minefields are often littered with metallic objects (e.g., fragments from exploded munitions). Hence, false alarms are common, limiting the utility 

In an effort to address the problem of detection of low-metal-content mines, DARPA funded development of new sensor technologies that focused on detection of the single material unique to all landmines—the explosive. The Fido sensor was one of several explosives vapor detectors developed under this program. Unless specified otherwise, the data presented in this section was collected during field tests of this sensor. 

As discussed previously, military-grade TNT is not a pure material, containing additional nitroaromatic constituents at concentrations of up to several percent by mass [4], Some of these explosive-related compounds (ERCs) have been shown to be significant contributors to the chemical fingerprint of a landmine [5, 7], Of the ERCs found in TNT, those that are most prevalent in the headspace vapor of TNT include 2,4-DNT, 2,6-DNT, 1,3-dinitrobenzene (1,3-DNB), and 

3 pg per mine per day. Flux rates were also measured into water. The flux rate of 2,4-DNT from a polystyrene-cased PMA2 AP mine into water was a factor of 30 larger than into air, and for TNT was a factor of 400 larger. It was estimated that the flux rate into wet soil would be intermediate between the air and water values. This has important implications for sensing mines since soil moisture content will likely influence the rate of release of ERC from mines. 

These studies have resulted in a better understanding of the conditions that are necessary to produce vapor concentrations of ERC at the surface of the ground sufficient for mine detection using our sensor. 

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