Many soil physical and chemical properties interfere with landmine detection. Prior knowledge of these properties would improve detection technology selection and increase demining safety and efficiency. Developments in rapid mapping of these properties over wide areas is essential to meet military and economic constraints. Fusion of multiple detection technologies is also essential to overcome detection signal interferences. For these purposes, rapid mapping by use of remote sensing is being tested, starting with electrical conductivity mapping by radar remote sensing. Laboratory induced-polarization (IP) is also being tested to develop techniques to discriminate between electromagnetic signals from metallic particles in landmines and in soil, for regions with detection interference. Key physical models of soil are being developed for fusion of various landmine detection systems and to explain remote sensing responses to soil.
Radar satellite tests carried out over the Canadian Forces Base Suffield (CFBS; Alberta, Canada) in 2004 and 2005 indicated 10 areas for possible high clay content and electrical conductivity. Eight of these were validated by soil maps and Landsat clay images. Two had high organic content with physical characteristics not known at present. Studies on soil with fine-grained iron-oxide powder and on iron with varied degrees of corrosion show that spectral-IP is sensitive to iron or iron-oxides regardless of their state. Soil has layered structure consisting of various grain-size combinations, but its physical characteristics are significantly influenced by whether its clay content is above or below a critical clay content (15 to 25 %). Results of these tests are discussed in this paper with explanations using the soil physical model.
Many soil physical and chemical properties interfere with landmine detection signals. Since prior knowledge of these property distributions would allow appropriate technology selection and efficient demining operations, rapid mapping of these properties over wide areas are considered for meeting military and economic constraints. As soil electrical conductivity (EC) interferes with widely used detection systems, such as metal detectors and ground penetrating radar, we have started with developing a rapid mapping technique for EC using remote sensing. Electromagnetic surveys are proven methods for mapping EC, but do not provide all information required for demining. Therefore, EC prediction by imaging of soil moisture change using radar satellite imagery acquired by RADARSAT is being tested in eastern Alberta (Canada) and northern Mississippi (U.S.A.). Areas of little soil moisture change with time are associated with high moisture retention and high clay content, suggesting higher EC. These soil characteristics are also associated with trafficability.
RADARSAT soil moisture change detection images for eastern Alberta identified five areas with possible high moisture retention characteristics. Validation by soil and trafficability maps verified the predictions for more than half of the areas. Lack of some prediction accuracy is considered due to image acquisition timing and lack of physical property knowledge of some soil constituents.
Physical properties, such as soil moisture, magnetic susceptibility and electrical conductivity (EC) are sources of signal interference for many landmine detectors. Soil EC mechanisms and their relationship to moisture are being studied to increase the soil EC prediction accuracy by radar remote sensing, airborne and ground electromagnetic (EM) methods. This is required for effective detection operations in problematic regions of the world. Results indicate that responses of free water and bound water to drying rates and EC are very different, to the extent that moist clay-poor soil may have lower EC compared to dryer clay-rich soil at certain moisture contents. These suggest that soil EC prediction should start with analyses of radar remote sensing data acquired on separate days, followed by high frequency airborne EM surveys, and validation by ground EM surveys and laboratory soil sample analyses. Due to the various expertise required, a team of relevant experts (e.g., geology, geophysics, remote sensing, petrophysics, agriculture, soil physics, electrical engineering and demining) should be organized to provide information on detector viability for demining in problematic areas in the world. It is also proposed to develop wide frequency band EM systems to provide much of the required information in one measurement.
Factors controlling the distribution and intensity of soil magnetic susceptibility (MS) and electrical conductivity (EC) were investigated. The purpose was to determine the factors to be considered in predicting MS and EC characteristics of soils in landmine-affected areas and in developing effective landmine detection systems and strategies. Results indicate that knowledge of bedrock geology, soil weathering and transportation (wind and water) history is essential to predict soil MS and EC characteristics. These factors determine the distribution, concentration and mineral type (e.g. ferromagnetic and clay minerals) in soil. For example, fluctuating water tables in tropical climates could produce soils rich in ferromagnetic minerals at the surface, even though their source (bedrock) may have low iron content. Also, subsequent weathering may change these minerals to high or low MS values. Although high clay concentrations homogeneously distributed may not produce high soil EC values, a low clay content concentrated in a single layer may produce extremely high EC values. These suggest that bedrock geology, agricultural soil, air photo and airborne geophysical survey maps can be used for predicting soils MS and EC characteristics of landmine-affected areas. Laboratory and surficial geophysical surveys are techniques for use in validation.
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