Moisture Effects in Soils Using a Frequency Domain Metal Detector

It is reported by experienced deminers that the existence of moisture in soils complicates the detection of buried land mines. In this work we examine the influence of water in two different sample soil types (sand and clay soil) on the magnetic field induced by a mine surrogate and thus on the quality of the detector's audible signal when using a frequency domain metal detector. The results of our studies prove that with increasing moisture content the amplitude of the received response voltage in both operating frequencies is diminished and that the level of diminution depends on the soil type. To investigate the influence of different soils and moisture levels a comprehensive measurement activity has been accomplished. The received signal data have been smoothed and evaluated statistically. For this purpose firstly the voltage intervals defined by the overall extreme values of the pure soil measurements are evaluated, so the intervals include all inhomogeneities of the ground, and compared with other different test scenarios containing mines. The additional obtained result that the extremal intervals of the wet soils converge to the corresponding intervals of dry soils when desiccating underlines the expected influence of moisture content. As a first try to categorize and differentate mines buried in different depths, soil types and moisture levels, a self organizing feature map to merge and categorize the high-dimensional, complex spatial signal vectors obtained when moving the sensor head over a mine buried in the ground has been trained and applied to the test data.