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Landmine detection problem: The role of the soil DETERMINATION OF SOIL MOISTURE. Vlado Valkovi ć Department of Experimental Physics, Ruđer Bošković Institute, Bijenička c.54, 10000 Zagreb, Croatia .
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Department of Experimental Physics, Ruđer Bošković Institute, Bijenička c.54, 10000 Zagreb, Croatia.
Co-authors:Jasmina Obhođaš, Davorin Sudac, Karlo Nađ, Ruđer Bošković Institute, Zagreb, Croatia;Giancarlo Nebbia, Giuseppe Viesti, Istituto Nazionale di Fisica Nucleare,Sezione di Padova, Padova, Italy
Work done under for Project: DIAMINE, Contract IST-2000-25237, under subcontract between Istituto Nazionale di Fisica Nucleare, Padova, Italy and Ruđer Bošković Institute, Zagreb, Croatia
There are 19 soil samples collected for the soil bank available for testing procedures when capabilities of mine detection methodologies are going to be evaluated. These soils represent different soil types, vegetation, ground configuration and climate zones in landmine contaminated areas of Croatia. Preliminary determination of some basic physical and chemical properties (texture, silicate analysis, major and trace element analysis) for all soils has been performed.
Soil moisture variations have been monitored at six locations in Croatia. Locations were chosen with the aim of covering different Croatian climate zones and representative types of soil in landmine affected areas. The locations are: Zagreb and Karlovac in the western part of Croatia, three locations in Zadar and its surroundings representing the south ofCroatia, and Križevci in the northern part of Croatia
Surface soil moisture variability for different soil types at different locations were measured by using two methods: Theta probe (Manufacturer: Delta-T, UK), ML2, responding to dielectric properties of soil, and gravimetric method.
Each time a surface area of 80 cm by 80 cm was investigated by measuring soil moisture at points separated by 20 cm. Probe ML2 contains 3 rods arranged in a circle around a central rod. This creates a defined cylindrical zone of measurement, 60 mm long x 26.5 in diameter (mass ~50 g).
For the gravimetric method top 4 cm of soil were collected with plastic cup of diameter d= 55 mm ( mass ~100 g). Since the ML2 probe displays result in w% determination of soil density was required for comparison of two sets of data.
The errors of the measurements were as follows: for ML2 probe the error was ≈5%, while for gravimetric method the relative error was estimated to be ≤10%.
Surface soil moisture (mass %) variations (locations Zagreb-graphs a. and b.; Zadar – Punta Mika, graphs c. and d.) as measured on undisturbed pseudogley with grass cover. (a and c) with ML2 probe, depth of measurements: 0-6 cm; calculated assuming w=1.2742 g/cm3. (b and d) with gravimetric method, depth of measurements: 0-4 cm.
The problem of landmine detection and identification is a problem of detection and identification of theexplosive and its casing buried in the soil. Soil, due to its elemental composition and themoisture content, produces a background or noise in thespectroscopic measurements done for landmine detection and/or identification. The goal of spectroscopical methods is to maximize the signal to noise ratio.
Since theneutron backscattering technique, NBT, measures the number of hydrogen atoms, we have introduced a concept of the critical value corresponding to the equality of the number of hydrogen atoms in the interrogated object and the surrounding soil. This critical value is characteristic of soil type and landmine type.
Soil water content is the key attribute of soil in NBT landmine detection application. If the critical value of the soil water content is reached, the detection of landmine explosives is not possible. The critical value is reached when the density of the hydrogen atoms in the landmine is equal to that in the background soil.
It is recommended that soil moisture content for NBT application do not exceed 10 kg.kg-1 (10 % Mass).
According to preliminary results of soil moisture monitoring of different types of soils in different parts of Croatia, with the aim to cover versatile textures and structures of soils and versatile hydrometeorological regimes, the values of soil moisture often exceed the NBT soil moisture critical value. Considering this, the results presented here suggest that NBT is not suitable for landmine detection in Croatia, but it could be recommended to countries with arid climate were arid soils with soil moisture below 10 % Mass are quite common.