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The application of thermography to detect buried objects (e.g. antipersonnel mines in the humanitarian demining) has been limited to mine-contaminated regions with homogeneous and vegetationless soils. Realistic non-homogeneity induces considerable noise superposed to the thermal response of the buried object. One source of noise is surface non-homogeneity, interpretable as a quasi-random signal, which screens the thermal response of the buried object. This interpretation allows for noise reduction using advanced thermogram processing algorithms, such as Independent component analysis. We apply it to thermograms obtained using controllable experimental conditions and a realistic three-dimensional, non-stationary heat transfer program. Numerical estimates of the degree of soil non-homogeneity, which can be reduced in thermograms, are obtained for a particular, representative class of buried objects and soil surface non-homogeneity. In particular, the dependence of the results on concentration of surface point-like nonhomogeneities is determined.

Landmines are part of a complex system with variable characteristics that may change with time. If thermography is applied on such a system, the most significant characteristics of resulting thermograms is overcritical noise which has severely suppressed the application of thermography for landmine detection for humanitarian demining. The attempts to realise as much as possible of the thermography potential motivated concentrating onto sources of noise in buried objects thermograms, in particular onto variations in mine orientation relative to the soil normal. The experiments reported in this paper were performed in order to investigate the influence of angle between the local vertical axis and mine symmetry axis, the angle between the local vertical axis and soil surface normal, and the object depth. The influences are quantified and ranked through the statistically planned experiment. The strongest influence is the statistical interaction of depth and angles. According to the statistical test these two combinations are significant influences. The results indicate that the application of modern thermography in humanitarian demining is to be broadened by including the variations in mine orientation.