·Table of Contents ·Workshop - Landmine Detection Equipment | Buried mine and soil temperature prediction by numerical modelP. Pregowski,PIRS, Pregowski InfraRed Services, Warsaw, PL, Email : pirspp@warman.com.pl W. Swiderski, Military Institute of Armament Technology, Zielonka, PL, Email : zak_13@witu.mil.pl R.T. Walczak, K. Lamorski, Institute of Agrophysics, Polish Academy of Sciences, Lublin, PL, Email : rwalczak@demeter.ipan.lublin.pl Contact |
Fig 1 : |
Formula applied above, proposed by Wijk and de Vries, is too general to solve considered problems.
The method of our modelling can to be shortly characterised as follows. We assume that there is no natural spatial heterogeneity of soil thermal parameters, and that the heat and water fluxes depend on the atmospheric conditions, following to the formula : R_{n}+H_{s}+LE+G=0 where: R_{n} - net radiation at the soil surface, H_{s} - sensible heat flux exchanged between soil surface and atmosphere, L - latent heat of vaporizing, E - water flux at the soil surface, G - heat flux at the soil surface.
The following processes were taken into account: water conductivity resulting from soil water potential gradients; thermal conductivity resulting from temperature gradients; surface soil processes: vaporising and energy exchanging with the environment; variability of thermal properties caused by mine buried in soil, and by differences in water content and soil density. Flux of energy in the soil is calculated from the Fourier's equation using the of average value of thermal conductivity coefficient "l
" calculated on the base of model elaborated in Lublin Institute of Agrophysics[8]. Transport of water in the soil profile is calculated using Richard's equation and water retention in the soil using Mualem-Van Genuchten model. Mine is to be considered as a roller, so the whole system, soil-buried mine, has axial symmetry, what simplified the calculations a lot. Differential equations, which describe heat and water transport in the soil, are spatially approximated using finite differences method on a rectangular grid. For these approximation for the space net, Crank-Nicholson's method was partly modified.
Fig 2 : | Fig 3 : |
Fig. 4 presents thermal visibility of the mines buried at depth of 5cm, - resulted from various amplitudes of the solar irradiation(200-500)Wm^{-2} and unchanged cyclic changes the air temperature and the solar heating versus time. Inversions of thermal signatures and their delay in time, caused by both differences between solar activity and air temperature maximums as well as top layer thickness influence, are clearly seen. Fig. 5 shows simulated temperature distributions in soil at the end of heating (a) and after long cooling (b). Fig. 6 is simulation of thermal signature of the buried mine at the end of heating.
Fig 4 : | Fig 5 a,b: | Fig 6 : |
Fig 7: collects example of IR thermograms of plastic mine at various time of heating/cooling process. |
Thermograms as above were obtained at laboratory, under controlled conditions, with the aim to verify and to tune the numerical model. Similar tests in the field, altough much more complicated and time consuming, are planned for this summer and autumn and will be executed on the specialised agro-climatical stand in IA PAS Lublin.
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