Detection and discrimination of unexploded ordnance (UXO) can be seriously hindered by the presence of magnetic rocks and soils. In regions of highly magnetic soil, magnetic and electromagnetic (EM) sensors often detect large anomalies that are of geologic, rather than metallic, origin. Under SERDP exploratory development (SEED) project MR-1285, the research team used numerical simulations to examine the effect of magnetic soil on the static magnetic method and time-domain EM method in UXO discrimination problems. The team assessed the level of soil response that severely affected the reliability of current discrimination algorithms based on geophysical inversion. It was clear from this research that the successes of these, and other, data processing algorithms require an understanding of the spatial characteristics of the susceptibility and the dependence of susceptibility on frequency.
This project focused on practical questions regarding the physical understanding of magnetic soils, how to generate useful site characterizations of magnetic properties, and how to use information from the site characterization to process magnetic and EM data. Specific technical objectives include: (1) understand the geologic origins and physics of soil magnetization, (2) develop protocols and practical procedures for characterizing site magnetization, (3) develop methods and procedures for removing the effects of soil responses from magnetic measurements, and (4) develop methods and procedures for preprocessing EM data.
In this project, the research was guided by practical questions that arise from four sites with different magnetic soil properties. The spatial distribution and frequency dependence of susceptibility were studied and its effects on different sensor modalities quantified. The geological factors governing the spatial and grain size distribution of magnetic iron oxides, and hence their susceptibility, also were studied. New filtering techniques that incorporate geostatistical information and a physical understanding of the phenomenon of complex magnetic susceptibility were developed.
Through fundamental knowledge of the spatial distribution and frequency dependence of susceptibility and its effects on different sensor modalities, new filtering techniques have been developed that incorporate geostatistical information and a physical understanding of complex magnetic susceptibility. These approaches identify and remove the effects of magnetic soil from geophysical data in UXO clearance.
This project addressed one of the Department of Defense’s most pressing environmental problems; that is, the efficient and reliable identification of UXO, particularly in magnetic environments, without the need to excavate large numbers of non-UXO at high costs.