Soil impact on metal detector performance and soil characterisation maps

Transcription

1 Soil impact on metal detector performance and soil characterisation maps H. Preetz & J. Igel Leibniz Institute for Applied Geophysics, Hannover, Germany UNMAS/GICHD Mine Action Technology Workshop 2010 Influences on the detectability of targets Detection technique Human factor Probability of detection Environmental conditions Target characteristics Soil Weather etc. Man-made clutter 1

2 Metal detector mode of operation primary field transmitter coil receiver coil eddy current secondary field mine relevant parameter magnetic susceptibility κ electric conductivity σ Time domain metal detector at frequency dependent susceptibility Transmitter coil Receiver coil I(t) U ind (t) t Soil Metal object Induced voltage (V) half space with metal object susc. t -5/2 t -1 Time (s) 2

3 Soil parameters with influence on metal detectors Physical parameters - magnetic susceptibility κ - frequency dependence of magnetic susceptibility - electric conductivity σ Soil parameters - mineral compound - bulk density - soil moisture - soil texture etc. Heterogeneity of the parameters - bulk density - stone content - vegetation etc. Namaacha / Mafavuka magnetic susceptibility m m SI * 10exp Measurement and classification of magnetic susceptibility European standards workshop agreement CEN/CWA (2003) Classification Magnetic susceptibilityκ 10-5 SI neutral 0-50 moderate severe very severe >

4 Magnetic susceptibility of tropical soils neutral moderate severe very severe 200 appr. 600 soil samples from 15 countries of tropical regions from our soil archive number of readings very severe 15% severe 21% moderate 30% neutral 34% magnetic susceptibility [SI x 10-5] more than 1/3 of all investigated soil samples show severe influence on MD Magnetic susceptibility of soils with different parent rocks dependence on parent rock dependence on degree of weathering very severe susceptibility [SI x 10-5 ] severe moderate neutral ultrabasic basic acidic clay, clay slate phyllite sandstone parent material 4

5 - Classification system - soil influence on metal detectors Parent Rock ultrabasic basic/ intermediate acid Clay/ -slate Ignoring Weathering Degree of Weathering strong medium low Phyllite - Sandstone Limitations of metal detector: neutral (0 50 * 10-5 SI) moderate (50 500) severe ( ) very severe (> 2000) Example: Geological map of Southern Mocambique 5

6 Example: Soil map of Angola Editing of the soil map 6

7 Classification of soils in Angola according to the degree of weathering Degree of weathering (schematic) Soil types according to FAO (1990), WRB (2006) Soil map of Angola (Min. do Ultramar, 1965) Degree of weathering according to Preetz et al. (2008) (all other soils) (low) Nitisols (NT) Lixisols (LX) Acrisols (AC) Ferralsols (FR) Plinthosols (PT) slightly leached to leached soils (Lessivés) fersiallitic soils paraferralitic soils, slightly ferralitic soils slightly ferralitic soils, typical ferralitic soils soils with lateritic materials near the surface 3 10 (low) 3 10 (low) 1 3 (moderate) 0 1 (high) 0 1 (high) Classification of the FAO soil types according to magnetic susceptibility Parent Material Soil Types Magnetic Susceptibility Median (90 % Quantile) basic / ultrabasic volcanic rocks Ferralsols / ferralic... Plinthosols / plinthic.. Acrisols... (all other soils) acid volcanic rocks / claystones / phyllites / sandstones Ferralsols / ferralic... Plinthosols / plinthic... Acrisols... (all other soils) neutral moderate severe very severe 7

8 Prediction of magnetic susceptibilities (median) Prediction of magnetic susceptibilities (90 % quantiles) 8

9 Incorporation of impact communities according to SAC Conclusions Soil characterisation can be helpful when planning demining operations The crucial soil parameter, magnetic susceptibility, is easy to measure A classification system has been created Easily available geodata from soil maps or geological maps for instance can be used for that The classification system can be intersected with geodata by means of a GIS Predictions on potential failures of metal detectors can be made with this system Journal of Mine Action, 13.1,