Numerical Simulation of Thermal Signatures of Buried Mines over a Diurnal Cycle

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.