Gichd

Trace and vapour explosive detection, which aims eventually to complement or replace currently used Mine Detecting Dogs (see the corresponding section), consists in the chemical identification of microscopic residues of the explosive compound, either in vapour or in particulate form (or both).

  • Vapour refers to the gas-phase molecules emitted from the explosive´s surface (solid or liquid) because of its finite vapour pressure, and
  • Particulate refers to microscopic particles of solid material (typically down to sub-picogram size - 1 picogram of TNT contains about 2,6 billion molecules) that adhere to and contaminate surfaces that have, directly or indirectly, come into contact with an explosive material.

A sample has to be acquired in the field and either used directly in a portable detector, or transported to the analytical device (a contrast to bulk detection in particular). Trace particle detection can potentially detect samples of explosive material of a few picograms at the detector, equivalent to ppt concentrations. Even greater sensitivities are certainly achievable (chromatography can already achieve this in laboratory systems), but whether this can be done for field portable systems remains to be seen. In practice, the need for a field system depends on the application and working methods. Some users, most notably Mechem in S Africa, have preferred to focus on REST (Remote Explosive Sensing Technique) systems. In the Mechem MEDDS (Mechem Explosive and Drug Detection System) the sample is brought to the detector – dogs in this case! This permits the dogs to work under more closely controlled conditions with fewer distractions, and allows the sample to be sniffed by a larger number of dogs. Cross contamination and handling issues are of great importance when dealing with picogram level samples.

Trace and vapour explosive detection is increasingly seen as a method for Area Reduction and not for locating individual mines. The use of a consistent negative result to declare a defined area free from contamination (Area Reduction) offers such significant benefits that it is is already used by some operators under certain circumstances. Currently the most common method is to use dogs to scan the area.

Several automated trace detection technologies have been in use for quite some time, for example in the aviation security sector and for the detection of drugs, and are described in the referenced documents. Their application to landmine detection has, however, to take into account the effects of explosive transport in soil which are complex and strongly dependent on any water flow and other parameters. Concentrations of vapour in a mined area many be several orders of magnitude lower than in a screening portal in an airport. There is some evidence that weather and soil conditions lead to samples not being repeatable.

Studies and measurements on environmental fate and transport of explosives have been carried out, for example, at the Sandia National Labs, CRREL (USACE Engineer Research and Development Center, Cold Regions Research and Engineering Laboratory), FOI (Swedish Defence Research Establishment), DRES (Defence Research Establishment Suffield, Canada). MECHEM (South Africa) has accumulated practical field experience on the subject as have the partners in the BIOSENS project. In general these studies confirm that there is a large influence of environmental parameters, target history, and other factors, on the variables of interest (explosive vapour and particle concentration), and the quantity of explosive substance available for detection can be very small.

Sensor systems for field application need to have an appropriate sampling system (of the air, vegetation or the soil), possibly including filtering to increase concentration. Suitable operational procedures also have to be defined. Up to now it seems that sensors either have insufficient sensitivity, are too slow or too large to be used in field applications, and the nature of explosive movement from mines - particularly microscopic particles - has made defining procedures very challenging. Some evidence is emerging that sampling is now the key problem.

In Europe the Biosensor project has attracted some attention and is described in a separate section. In this case one of the systems under development is targeted specifically at landmine detection for humanitarian demining, to be employed for verification and area reduction purposes.

In the US a large three-year project was started in 1997 by DARPA (the US Defense Advanced Research Projects Agency) with funding of about 25 million US$. The aim was to develop an electronic dog’s nose that can be used reliably in the field (“Dog´s Nose” project). One of the outputs was the extremely sensitive Nomadics fluorescent polymer explosive detector.

Several further sensing systems, such as Ion Mobility Spectrometers (IMS), have been and are being tested for the detection of landmines.

Significant further work remains to be done on understanding how to obtain samples reliably and with statistical confidence, on vapour and particulate transport mechanisms and other aspects of vapour and particulate detection, as well as on the detectors themsleves. There is not even any general agreement yet on how dogs manage to find mines and what they are actually sniffing.

The huge challenge that the physical environment (particularly the soil) presents for vapour / trace detection is perhaps highlighted by the decision of a US programme which will provides €58M over an eight year period for demining technology to target 60% of this funding towards soil and environment research.

For more information


Record updated on : 13 March 2014
Record id : 11

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