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The ability to interrogate objects buried in soil and ascertain their chemical composition in-situ
would be an important capability enhancement for both military and humanitarian demining. Laser
Induced Breakdown Spectroscopy (LIBS) is a simple spark spectrochemical technique using a
pulsed laser. Recent developments in broadband and man-portable LIBS provide the capability for
the real-time detection at very high sensitivity of all elements in any target material because all
chemical elements emit in the 200-940 nm spectral region. This technological advance offers a
unique potential for the development of a rugged and reliable man-portable or robot-deployable
chemical sensor that would be capable of both in-situ point probing and chemical sensing for
landmine detection.
Broadband LIBS data was acquired under laboratory conditions for more than a dozen different
types of anti-personnel and anti-tank landmine casings from four countries plus a set of antitank
landmine simulants. Subsequently, a statistical classification technique (partial least squares
discriminant analysis, PLS-DA) was used to discriminate landmine casings from the simulants and
to assign "unknown" spectra to a mine type based upon a library classification approach. Overall, a
correct classification success of 99.0% was achieved, with a misclassification rate of only 1.8%.
This performance illustrates the potential that LIBS has to be developed into a field-deployable
device that could be utilized as a confirmatory sensor in landmine detection. The operational
concept envisioned is a small LIBS system that is either man-portable or robot-deployed in which a
micro-laser is contained in the handle of a deminer's probe, with laser light delivered and collected
through an optical fiber in the tapered tip of the probe. In such a configuration, chemical analysis
could be readily accomplished by LIBS after touching the buried object that one is interested in
identifying and using real-time statistical signal processing techniques to accomplish "mine/no-mine"
discrimination and even object identification if a material library could be constructed prior
to analysis.
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