The ability to detect buried land mines under a wide variety of environmental conditions is an important Army requirement. Both for interpreting signatures of mines and to ensure appropriate modeling of mine and background signatures, it is important to understand the phenomena that result in different signature patterns. The dynamic signatures can change quickly in time due to changing meteorological conditions and their impact on the mine, the soil, and on the mine-soil interaction. In field tests, infrared measurements of surface and near surface mines have shown anomalous concentric thermal signatures around the mine. The cause of these irregularities is not known. We conduct numerical multidimensional finite element calculations to investigate interactions between the meteorological conditions, the mine, and the nearby soil to elucidate the cause for these signatures. Both in-situ temperature measurements and model results show that thermal interactions between the mine and the soil are responsible for the signatures. The warm area around the mine in the nearby soil is predominant primarily at night. The warm ring effect is most likely to exist in dry soil and for mines whose heat capacity exceeds that of the soil, resulting in thermal dominance of the mine in the coupled mine-soil thermal regime. Wet soils are less likely to display the thermal contrast of the warm ring. Improved understanding of physical interactions between the mine and the background may facilitate improved discrimination between signatures of mines and of false alarms.
Areas subject to military conflict or military training sometimes contain unexploded ordinance and/or explosives residues resulting from detonations. A variety of past field and modeling studies have investigated the behavior of explosives in soils in warm climates, but the behavior in cold climates, including frozen soil and snow, has been less studied. In northern areas of military conflict, and at Army military training grounds in cold regions, winter weather exists for many months of the year. The impact of temperature and moisture changes in the soil, due to changing weather conditions, can have a large effect on the fate and transport of the explosives. The basic transport parameters for the behavior of the contaminant in frozen soil are unknown, yet these parameters are needed for problem assessment both for simple estimates and full numerical studies. In this paper we discuss sample results of controlled laboratory experiments performed to investigate the diffusion of 2,4-DNT through sand, under two conditions each of temperature and moisture. Based on the experimental data we present preliminary effective diffusion coefficients for the conditions. The concentrations show clear transport of the contaminant due to vapor diffusion and sorption. Sorption is a controlling feature of diffusion of explosives in sand. Diffusion rates and concentration on the particles increase with temperature. In both frozen and unfrozen sand, higher moisture content causes faster diffusion rates but lower particle concentration levels than in the corresponding dry cases.
The detection of buried mines is important to both for humanitarian and military strategic de-mining both at home and abroad, and recent efforts in chemical detection show promise for definitive identification of buried miens. The impact of weather has a large effect on the fate and transport of the explosives vapor that these systems sense. In many areas of military conflict, and at Army military training grounds in cold regions, winter weather affects military operations for many months of the year. In cold regions, the presence of freezing ground or a snow cover may provide increased temporary storage of the explosive, potentially leading to opportunities for more optimal sensing conditions later. This paper discusses the result of a controlled laboratory experiment to investigate explosives diffusion through snow, quantitative microscopy measurements of snow microstructure including specific surface, and verifications of our transport model using this data. In experiments measuring 1,3-DNB, 2,4-DNT and 2,4,6-TNT we determined an effective diffusion coefficient of 1.5 X 10-6 cm2/s from measurements through isothermal sieved snow with equivalent sphere radius of 0.11 mm. Adsorption is a major factor in diffusive transport of these explosives through snow. The data was used to verify our finite element mole of explosives transport. Measurements and model results show close agreement.
KEYWORDS: Explosives, Atmospheric modeling, Land mines, Diffusion, Mathematical modeling, Systems modeling, Chemical species, Liquids, Soil science, Solar radiation models
The detection of buried mines is important to both the military and to civilians, and the possibility of chemical detection may provide a more definitive identification. Understanding the transport of explosive vapors through soil or snow is a major step in the detection problem. In cold regions, the presence of freezing ground or a snow cover complicates the situation, yet also may provide temporary storage of the explosive, potentially leading to opportunities for more optimal sensing conditions later. This paper discusses preliminary work towards adapting an existing 2D heat, mass, and chemical vapor transport model to the problem of explosives transport. The model, originally developed for simulating heat and mass transport through snow under a variety of meteorological conditions, shows promise for simulating explosives vapor transport for buried mines.
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