An analysis of a thermal imaging method for landmine detection using microwave heating

A land mine detection method based on measuring the differing thermal respo nse rates of the sand above and beside a buried dummy mine has been investi gated in laboratory experiments. Differing response rates are created when the sand is heated by a microwave generator, and then cooled by forced conv ection. In the experimental investigation, a surrogate mine(1) is buried in sands which have a water content of 5% and 10% and in sand that is oven-dr ied. The results show that evaporative cooling at the surface of the sand i s the main mechanism controlling the surface temperature. When a substitute mine is buried in sand, the temperature response rate of the surface above the mine changes during the heating part of the process. This change is du e to a reduction in the rate of evaporative cooling in this region. In mois t sand, the surface temperature differences of 1.5 degreesC between the san d above the mine and the sand beside the mine have been measured and a resu ltant infrared photographic image of the mine can be readily observed. The tests involving dry sand show that there is some heating of the sand su rface by vapour condensation. The effect of this condensation is difficult to interpret since the migration of moisture into the sand cannot be evalua ted. When the condensation effect is ignored, the analysis can be used to d emonstrate the change in the values of surface temperature difference durin g cooling. Infrared photographs taken during the dry-sand tests show that t he location of the mine can be observed where the mine is buried at 2 cm, b ut not at 3 cm. (C) 2001 Published by Elsevier Science B.V.