Small-scale variability of electromagnetic soil properties and their influence on landmine detection: How to measure, how to analyse, and how to interpret?

摘要

The small-scale variability of physical soil properties has a negative influence on ground exploration with physical sensors. This particularly holds true for small target objects like landmines. Studies were carried out to determine magnetic susceptibility, electric conductivity and dielectric permittivity of natural soils. The spatial variability of the field data is quantitatively characterised by means of geostatistical analysis. We present field measurements on different soils types in Germany and on former minefields in Mozambique. The spatial distribution of magnetic susceptibility is governed by the mineral composition of the soil and its stone content. The correlation lengths are in the range of a few meters. In contrast, electric conductivity and permittivity is mainly determined by soil moisture. Due to the small-scale variability of topsoil water content, these two electric properties often feature very small correlation lengths in the range of decimeters. By way of example, the influence of soil variability on landmine detection is illustrated for radar sensors. Geostatistical simulation techniques are used to generate random soil models which are used for realistic finite-differences (FD) calculations of electromagnetic wave propagation. Permittivity variations appear to have a greater influence on radar detector performance than conductivity variations and can mask the signals from the mines.