* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Thermal signatures of land mines buried in mineral and organic soils
Survey
Document related concepts
Plant nutrition wikipedia , lookup
Soil horizon wikipedia , lookup
Soil erosion wikipedia , lookup
Soil respiration wikipedia , lookup
Crop rotation wikipedia , lookup
Terra preta wikipedia , lookup
Canadian system of soil classification wikipedia , lookup
Surface runoff wikipedia , lookup
Soil compaction (agriculture) wikipedia , lookup
Soil food web wikipedia , lookup
No-till farming wikipedia , lookup
Soil salinity control wikipedia , lookup
Sustainable agriculture wikipedia , lookup
Soil microbiology wikipedia , lookup
Transcript
Infrared Physics & Technology 43 (2002) 303–309 www.elsevier.com/locate/infrared Thermal signatures of land mines buried in mineral and organic soils––modelling and experiments K. Lamorski a, P. Prez gowski b, W. Swiderski c,*, D. Szabra c, R.T. Walczak a, B. Usowicz a a Institute of Agrophysics, Polish Academy of Sciences, Doswiadczalna 4, 20-290 Lublin 27, Poland b PIRS, Pregowski InfraRed Services, Zachodzacego, Slonca 36, 01-495 Warsaw, Poland c Military Institute of Armament Technology, Prymasa Wyszynskiego 7, 05-220 Zielonka, Poland Abstract A model of thermal phenomenon in soil developed to determine its thermal signatures in case of buried land mines in presented in the paper. Thermal signature values of a mine buried in two types of soil having different properties were compared using mathematical–statistical modelling. Results generated by modelling have been verified by laboratory experiment. 2002 Published by Elsevier Science B.V. Keywords: Thermal signature; Buried land mines; Modelling 1. Introduction The problem of the mines existing in the soil is an important problem in the world. Experts estimated that nowadays there exist about 120 millions of buried mines left in more than 60 countries around the world. There is a serious threat for civilian populations. Because of little efficiency of traditional methods on detection of buried mines in recent years many worldwide institutions have started the work to improve mine disposal effectiveness. Also in Poland the work has been carried out how to use infrared radiation for mine detection. Our obtained results were presented on many * Corresponding author. Tel.: +48-22-6833403; fax: +48-227819935. E-mail addresses: [email protected] (P. Pregowski), [email protected] (W. Swiderski), [email protected]. lublin.pl (R.T. Walczak). special conferences [1–3]. The basis for the thermovision methods of mine detection is a temperature signature of the mine on the soil surface. Thermal signatures of mines buried in the soil originate from different heat transport parameters of the soil medium and the mine. Efficiency of this methods is strongly connected with external condition and state and structure of the soil. In our existing works [4,5] as and in many other author’s works [6,7] was assumed that soil in which a mine is buried was homogeneous. In natural conditions most often the top layer of soil is organic and bottom layer is mineral. This problem is much more complicated and is considered in this paper. 2. Modelling The main issue in the thermodetection of mines buried in the soil is to determine proper conditions 1350-4495/02/$ - see front matter 2002 Published by Elsevier Science B.V. PII: S 1 3 5 0 - 4 4 9 5 ( 0 2 ) 0 0 1 5 6 - 1 304 K. Lamorski et al. / Infrared Physics & Technology 43 (2002) 303–309 for making measurements. Heat flow in the soil material is determined mainly by soil material properties and boundary conditions on the ground surface. As we have no influence on the natural meteorological conditions, which determines heat flux on the ground surface, we have to do our best to ensure optimal conditions for thermovision measurements. This includes choosing proper times and camera adjustments for making measurements. Good understanding of energy transport phenomena in the soil medium is crucial in this task. In our paper we present a physical model which describes heat transfer in the soil medium. This model is used for analysing heat transfer and mine signatures creation in layered soil medium, under natural conditions. Heat capacity and heat conductivity of mine may in general differ from surrounding soil heat transport properties. That makes it possible to detect mines by measuring soil surface temperature which is not homogeneous due to mine inclusion in soil medium. Heat flux qT in a soil medium may be described by the Fourier’s law (1) where k (W/m K) is thermal conductivity and rT (K/m) is a spatial gradient of temperature T. qT ¼ krT ð1Þ If there are no sources thermal in soil medium we can describe the energy conservation law in the form of continuity equation (2). Cv oT ¼ rqT ot ð2Þ Finally heat transport in the soil may be described in general by the following equation, which is a consequence of the energy conservation law and Fourier’s law. Cv oT ¼ rðkrT Þ ot ð3Þ This parabolic partial differential equation describes heat transport in isotropic, non-homogeneous medium. Volumetric heat capacity Cv (J/ m3 K) and heat conductivity k depend in general on spatial position. It is a well known fact [8,9] that the heat capacity of soil Cv and soil heat conductivity k depends on temperature and soil moisture. Due to that fact we have to take into account soil moisture content changes in our model. As it is described by Darcy’s law, water flow in porous materials takes place due to gradient of soil water potential. This is described by equation (4) where the soil water potential is a sum of two components. Pressure head h (m) which is associated with interactions between soil particles and water, is a function of soil moisture content. The second part of soil water potential is gravity head which is a consequence of gravity forces affecting soil water. Gravity head is simply a distance from somewhere defined reference level. In (4) qw (kg/m2 s) is a water flux, ql (kg/m3 ) is a water density and K (m/ s) is a soil water conductivity. qw ¼ ql Krðh þ zÞ ð4Þ The soil water conservation law we can write in the form of following equation, o ð ql h Þ ¼ rqw ot ð5Þ where h is a volumetric soil water content (m3 /m3 ). Darcy equation combined with a conservation law, gives Richard’s equation which describes soil water transport phenomena in the soil medium. Cw oh ¼ rð Krðh þ zÞÞ ot ð6Þ In this equation we have taken into account functional dependence between pressure head and soil moisture content h ¼ hðhÞ. Differential soil water capacity Cw (m1 ) which appears in this formulation of Richard’s equation is described by the following formula: Cw oh oh ð7Þ Eqs. (6) and (3) describe heat and water transport phenomena in any geometry despite of coordinate system. If we assume that soil transport parameters may only depends on vertical coordinate, and if we assume that other mines are far enough (Fig. 1), then we can describe our problem of heat and moisture transport in axial coordinates. Eqs. (6) and (3) take the following form in axial coordinates, when we K. Lamorski et al. / Infrared Physics & Technology 43 (2002) 303–309 305 The net radiation at the soil surface Rn (W/m2 ) is an energy flux exchanged at the soil surface due to radiation phenomena. Water flux of the water evaporating from the soil surface E (kg/s m2 ) generates energy flux due to latent heat of vaporisation L (J/kg). Sensible heat flux HS (W/m2 ) is exchanged between soil surface and atmosphere due to air convection. The soil surface is cooled or heated due to differences in air temperature and soil surface temperature. G is a net heat flux at the soil surface (W/m2 ), which is taken as a Neumann’s type boundary condition for the heat transport equation. The net radiation at the soil surface Rn is described by: Rn ¼ ð1 alÞIG þ R1 Sem ð11Þ where al is albedo of soil surface, IG is a global incoming radiation (W/m2 ), R1 is long-wave radiation of atmosphere (W/m2 ) and Sem is energy flux radiated from the soil surface due to its temperature. The long-wave radiation of atmosphere is calculated from the following formula [10]: 4 Fig. 1. The geometry of considered space in the model. discard dependence on angle u in axial coordinate system, which is the result of the assumed spatial homogeneity of soil profile: oT 1 o oT o oT ¼ rk k Cv þ ð8Þ ot r or or oz oz oh 1 o oh o oh ¼ rK K Cw þ þ1 ð9Þ ot r or or oz oz We have a system of two non-linear time dependent partial differential equations of parabolic type in two dimensions. We have to determine boundary conditions, initial conditions and functional dependence of transport parameters to solve them. On the bottom of calculation area and on the sides there are no-flow Neumann boundary conditions. Heat flux through soil surface may be calculated from the energy balance equation. Rn þ HS þ LE þ G ¼ 0 ð10Þ 1:2 R1 ¼ rðTa þ 273:16Þ ½0:605 þ 0:048ð1370Ha Þ ð12Þ where Ta is temperature of air (C) and Ha is absolute air humidity (kg/m3 ). Sem , is calculated as follows: Sem ¼ erðTs þ 273:16Þ4 ð13Þ where e is a soil surface emissivity, r is the StefanBoltzmann constant (W/m2 K4 ), TS is temperature of the soil surface (C). Evaporation rate and a sensible heat flux are described by the Penman type equations [10]. The Mualem and Van Genuchten model (14) of soil water retention curve is used to describe the dependence between soil moisture and pressure head. This model does not describe hysteretic behavior of soil moisture–pressure head dependence, which is common in real soils, but it is simple in adaptation in practical calculations. Soil water residual capacity hR (m3 /m3 ) is the amount of water which is bounded on the soil particles even in a dry state. The other parameters of that model are: hS (m3 /m3 ) is a volumetric saturated soil water 306 K. Lamorski et al. / Infrared Physics & Technology 43 (2002) 303–309 content, a and n are parameters without clear physical meaning. 11=n 1 h ¼ hR þ ðhS hR Þ ð14Þ n 1 þ ðahÞ Differential soil water capacity described by the Eq. (7) when using soil water curve formula (14) takes the form: n Cw ¼ n ð12n=nÞ ð1 nÞðahÞ ðhS hR Þð1 þ ðahÞ Þ h ð15Þ Soil water conductivity may be expressed as follows [4] in Eq. (16) when using the Mualem– Van Genuchten model for water retention. n o2 nþ1 n ð1n=nÞ 1 ðahÞ ½1 þ ðahÞ KðhÞ ¼ KS ð16Þ ðn1=2nÞ ½1 þ ðahÞn Soil heat capacity and soil heat conductivity may be calculated using a statistical model described elsewhere [2]. 3. Measurements In order to test the model introduced above at different but controlled in laboratory conditions the laboratory set-up was built (Fig. 2). Temperature profiles in soil consisted of top organic and bottom mineral layers were registered in the middle of experiment. There are two basic categories of soil material existing frequently in nature. Organic Fig. 2. Testing set-up. Table 1 Components of soils Organic matter Quartz Other minerals Zagrody (m3 /m3 ) Kuwasy (m3 /m3 ) 0.028 0.815 0.156 0.767 0.12 0.221 layer is determined buy the soil obtained from localities of Kuwasy and mineral from localities of Zagrody. These compositions of the soils are introduced in Table 1. All investigations were carried out using the AGEMA SW TE and LW thermal cameras and set of instruments for measuring: temperature on buried mine, temperature on profile of the soil, temperature on surface of the soil, moisture of the soil, irradiance of the surface and state of external conditions. The measurement field takes the central part of the set-up and the wooden specially isolated container with dimension 900 750 300 mm. The temperature sensor and plastic mine (radius 320 mm and height 85 mm) were placed inside the soil filled container in precisely determined spots. The mine was placed in the middle of the measurement field. Inside edge installed lamps determined dimensions of the container. 4. Results In Figs. 3–6 there are presented values of thermal parameters of mineral (Zagrody) and organic (Kuwasy) soils. These soils were used in computer simulation as well as in laboratory experiment. Values of the soil heat capacity and thermal conductivity were calculated using the model described earlier. These thermal parameters of soils are very different. This is caused by the different content of water and of organic material. Thermal conductivity of organic material, which is a basic component of organic soil is much lower than of quartz. This fact decides on values of thermal parameters of soils. In Fig. 7 is shown a comparison of change of temperatures in soil profile obtained from computer simulation and results obtained in laboratory experiment. These results were obtained for a soil profile where the top layer of organic soil was K. Lamorski et al. / Infrared Physics & Technology 43 (2002) 303–309 Fig. 3. Conductivity of sample mineral soil. r is bulk density (mg/m3 ). Fig. 4. Heat capacity of sample mineral soil. Fig. 5. Conductivity of sample organic soil. Fig. 6. Heat capacity of sample organic soil. 307 308 K. Lamorski et al. / Infrared Physics & Technology 43 (2002) 303–309 Fig. 9. Results of laboratory experiment. Fig. 7. Comparison of change of temperatures in soil profile by simulation and experiment. 3 cm and under it was immediately buried a mine placed in the middle of the soil containers. The centre soil was warmed by lamps about 60 minutes with power 500 W/m2 , water content w:c: ¼ 0:3. At the start external temperature was 20 C and then we cooled freely by 60 min at speed wind of 0.05 m/s. In Fig. 8 is shown an example of simulation of dynamics heat propagation for a laboratory system as in Fig. 2 and assumptions as above: Patterns of temperature in half vertical section of the Fig. 8. Computer simulation results. soil from the centrally placed mine for conditions as above. In Fig. 9 are shown examples of thermograms obtained in the middle of research of plastic mines in the laboratory set-up of Fig. 2. Thermograms from cameras LW present typical effect of thermal inertia in generating signatures of plastic mines. They introduce heating and cooling phase of mines for conditions as above. 5. Conclusions • Developed model made possible analysis of flow of energy in a soil–mine system and simulation of thermal signatures dependences on properties of soil and mine. • The laboratory experiment confirmed correctness of the accepted assumptions for the developed physical–mathematical model of heat and water flow in the soil. • Prediction of thermal signature of buried mines in mineral soil with the top layer of on organic type is much more complicated than for sandy soil. • We confirmed the large influence of the soil superficial layer on thermal signatures creation of buried mines. • Different external conditions and thermal features of the very dry and very wet soil or density K. Lamorski et al. / Infrared Physics & Technology 43 (2002) 303–309 differences of soils show that detection of the same mine could be possible provided that quite different criteria were used. References [1] P. Pregowski, W. Swiderski, Using of comparison method in IR thermal detection of buried mines, SPIE 3392 (1998) 781–800. [2] P. Pregowski, W. Swiderski, Detection of minefields using IR sensing and time-domain treatment method, SPIE 3079 (1997) 705–714. [3] P. Pregowski, W. Swiderski, R.T. Walczak, Surface and volume effects in thermal signatures of buried mines: experiment and modelling, QIRT (1998) 233–238. [4] P. Pregowski, W. Swiderski, D. Szabra, B. Usowicz, R.T. Walczak, Experimental Verification of Thermal Signature [5] [6] [7] [8] [9] [10] 309 Model for Mines Buried in the Sand, WITU, Zielonka, 2000, pp. 61–72, ISSN 11230–3801. K. Lamorski, P. Pregowski, W. Swiderski, R.T. Walczak, Buried mine and soil temperature prediction by numerical model, SPIE 4038 (2000) 1392–1403. S. Svaic, J. Stepanic, M. Malinovec, Detection of underground objects using thermography, in: 15th WCNDT, Roma, 2000, p. 768. A. Kamoi, Y. Okamoto, M. Eto, Experimental study on the effect of environmental fluctuations affecting thermal images of infrared radiometer, Thermosense XXII 402 (2000) 374–381. D.A. De Vries, Thermal properties of soil, in: W.R. van Wijk (Ed.), Physics of Plant Environment, North-Holland, Amsterdam, 1963, pp. 210–235. B. Usowicz, Statistical–physical model of thermal conductivity in soil, Polish J. Soil Sci. 25 (1) (1992) 25–34. D. Hillel, Environmental Soil Physics, Academic Press, San Diego, 1998.