Numerical simulation of thermal signatures of buried mines over a diurnal cycle

Abstract

Three-dimensional thermal and radiometric models have been developed to study the passive IR signature of a land mine buried under a rough soil surface. A Þnite element model is used to describe the thermal phenomena, including temporal variations, the spatial structure of the signature, and enviromental effects. The Crank-Nicholson algorithm is used for time-stepping the simulation. The mine and the surroundings are approximated by pentahedral elements having linear interpolation functions. The FEM grid for the soil includes a random rough surface having a normal probability density and speciÞed covariance function. The mine is modeled as a homogeneous body of deterministic shape having the thermal properties of TNT. Natural solar insolation (both direct and atmosphericscattered components) and the effects of convective heat transfer are represented by linearized boundary conditions. The behavior over a periodic diurnal cycle is studied by running the simulation to steady state. Finite element solutions for the thermal emissions are combined with reßected radiometric components to predict the signatures seen by an IR camera. Numerical simulations are presented for a representative target, a 25 cm anti-tank mine simulant developed by the US Army. The temporal evolution of the temperature distribution and IR signature are presented for both smooth and rough surfaces.

FPGA computation of the 3D heat equation

“…As can be noted, the temperature updating process of a pair of nodes requires a total of ten clock cycles, see Figs. [8][9][10]. It can also be seen in Figs.…”

“…The first term of this expression, q sun , can be estimated in a straightforward manner knowing the ground albedo and the local sun irradiation function [9,10]. In experimental setups, however, it can be easily measured with the help of low-cost equipment, which significantly reduces the complexity of the problem.…”

Analysis of a thermal imaging method for landmine detection, using infrared heating of the sand surface

“…These papers indicate that a typical value for both the characteristic dimension of the discontinuity and its depth beneath the surface will be less than 0.01 m. For the discontinuities detected, the ratio of depth to characteristic dimension rarely exceeds 0.7. Maierhofer et al [3] also used this technique to detect voids in a concrete block where both the characteristic dimension and burial depth of the discontinuity were an order of magnitude greater than those described by Almond et al When this procedure is applied to the detection of landmines, the discontinuity within the homogeneous soil is taken to be either the complete landmine [4,5], an internal component of the mine such as the gas space used to house its firing mechanism [6,7] or possibly even the disturbed soil created when the mine was buried [8]. Most of these discontinuities have a similar location: the upper surface of the mine.…”

“…Each of these heating processes introduces features which can assist or limit the overall detection process. In addition the use of pulsed thermography to detect landmines has been widely investigated both analytically [5,6,10] and experimentally [4,[7][8][9]13].…”

Studying the phenomena related to the IR thermographic detection of buried landmines

“…Another advanced model proposed in [2] enables the study of surface roughness and water mass transfer. Here we shall limit ourselves with some illustrations following from the results described in [1].…”