Today more than 75 countries are affected by landmines and/or unexploded ordnance (UXO). Since landmines are one of the cheapest weapons they are widely used and remain as a deadly hazard to civilians even many years after the end of armed conflicts. The recent number of officially registered casualties is nearly 6000 per year whereas the number of unknown victims is high. One of the reasons for the broad spread of landmines is the low cost of production which is partially only between 3 – 5 USD. However, the costs for clearing of a single landmine are between 300 and 500 USD.
Electromagnetic technique is widely used for the detection of landmines that are buried in soils. Among numerous search methods the metal detector remains the most common tool in landmine detection which is due to its low price and easy usability. UXO are usually easy to detect because of their high metal contents. In contrast, anti personnel mines are often difficult to find because of their low metal content which holds true in particular for modern mines.
The “soil problem” when using metal detectors occurs frequently in the following way: The instrument works on the basis of electromagnetic induction and detects metallic objects in the ground. However, modern anti personnel mines contain only little metal so that the operator of the metal detector is forced to work with the instrument in the most sensitive mode. The sensitive setup of the instrument evokes in turn a high false alarm rate which is caused either by small metal particles in the soil or by certain soil properties. Especially tropical soils often impede the performance of metal detectors used for landmine detection. False alarm rates of up to 1000 : 1 are not rare. The aim of our investigations is in particular to characterise and classify the crucial magnetic soil properties and to determine their influence on the performance of metal detectors.
Recently, dual sensors are more and more used which promise to reduce the false-alarm rate by combining both, a metal detector and a radar sensor. As opposed to metal detectors, ground-penetrating radar (GPR) can even detect mines which contain no metal parts. When searching for mines with GPR, it is in particular the small-scale variability of electric and dielectric soil properties playing a crucial role. Electric conductivity and dielectric permittivity show to correlate with soil-water content which, in turn, is strongly affected by precipitation, soil texture, vegetation and other related soil properties. Therefore, these soil properties are highly variable in space and time. Under disadvantageous conditions, i.e. if the contrast between the mine and soil is weak and soil moisture is heterogeneous, the GPR signature of the mine can hardly be discriminated from the background noise cased by the soil.
In order to determine soil influence on the used detectors, the following physical soil properties are analysed:
The physical properties are analysed in the lab and in the field. A part of the lab analysis is carried out in the rock magnetic laboratories of section S5 in Grubenhagen directed by Dr. Christian Rolf.
In a nutshell, the issues and objectives of the project are: