16-10-2010, 01:53 PM
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LAND MINE DETECTION IN BARE SOILS
USING THERMAL INFRARED SENSORS
Sung-ho Hong, Timothy W. Miller, Brian Borchers, and Jan M.H. Hendrickx
New Mexico Tech, Socorro NM 87801
Henk A. Lensen, Piet B.W. Schwering and Sebastiaan P. van den Broek
TNO Physics and Electronics Laboratory, The Hague, The Netherlands.
ABSTRACT
Soil surface temperatures not only exhibit daily and annual cycles but also are very variable in space and time. Without knowledge of the spatial and temporal variability of soil surface temperatures, it will be difficult to determine what times of day are most suitable for mine detection using Thermal Infra Red (TIR) technology. In this study we monitor the spatial and temporal variability of soil surface temperatures under a range of soil texture and soil moisture conditions on undisturbed plots and plots with a buried anti-tank mine in arid New Mexico. We also analyzed soil surface temperature measurements taken at the test facility for land mine detection systems at the TNO Physics and Electronics Laboratory under the temperate climatic conditions of The Netherlands. The measurements in both areas show a cyclic behavior of the thermal signatures of the mines during the day and night that can be predicted by physics of the mine-soil-sensor system. However, unexpected behavior of the thermal signatures in a silt loam demonstrated that prediction of thermal signatures of buried mines is not straightforward. Keywords: landmines, detection, thermal infrared, thermal signature, test facility. 1. INTRODUCTION Many sensors for landmine detection are affected by the water content, temperature, electrical conductivity and dielectric constant of the surrounding soil. The most important of these is soil water content since it directly influences the three other properties. Simunek et al. (2001) have conducted a modeling study to evaluate how soil texture and water affect the thermal signatures of land mines. They concluded that the maximum temperature difference between the soil surface above the mine and away from it, i.e. the strong thermal signature, depends in a complex manner on the thermal properties of the soil which depend on soil water and soil texture as well as the soil heat flux which changes with geographical location and time of the year. The strong thermal signature seems to appear in two six-hour intervals centered around 12:00 am and 12:00 pm but its exact time is very difficult to predict. To make matters worse, the weak thermal signatures frequently can also be found in these time intervals. Therefore, their modeling study indicates that the use of a single thermal sensor for instantaneous mine detection carries a high risk. On the other hand if a given area can be monitored constantly with a thermal sensor for twelve hours or longer a thermal signature may be detected if the signal to noise ratio of the mine-soil-sensor system allows so. Moreover, a thermal sensor can be useful in addition to other types of sensors like metal detector or ground penetrating radar in a multi-sensor fused mine detection system. DePersia et al. (1995) reported on thermal signatures in areas with land mines. Temperature differences between the soil surface above and away from the mine are attributed to differences in heat capacity between mine and soil as well as surface disturbance during mine burial. The major principle of thermal infrared (IR) sensors for mine detection is based on detecting localized temperature differences, apparent thermal contrast, introduced by the mines. The apparent thermal contrast also depends on background levels, and should be compared to the clutter contrast in order to derive the probability of detection of objects.
LAND MINE DETECTION IN BARE SOILS
USING THERMAL INFRARED SENSORS
Sung-ho Hong, Timothy W. Miller, Brian Borchers, and Jan M.H. Hendrickx
New Mexico Tech, Socorro NM 87801
Henk A. Lensen, Piet B.W. Schwering and Sebastiaan P. van den Broek
TNO Physics and Electronics Laboratory, The Hague, The Netherlands.
ABSTRACT
Soil surface temperatures not only exhibit daily and annual cycles but also are very variable in space and time. Without knowledge of the spatial and temporal variability of soil surface temperatures, it will be difficult to determine what times of day are most suitable for mine detection using Thermal Infra Red (TIR) technology. In this study we monitor the spatial and temporal variability of soil surface temperatures under a range of soil texture and soil moisture conditions on undisturbed plots and plots with a buried anti-tank mine in arid New Mexico. We also analyzed soil surface temperature measurements taken at the test facility for land mine detection systems at the TNO Physics and Electronics Laboratory under the temperate climatic conditions of The Netherlands. The measurements in both areas show a cyclic behavior of the thermal signatures of the mines during the day and night that can be predicted by physics of the mine-soil-sensor system. However, unexpected behavior of the thermal signatures in a silt loam demonstrated that prediction of thermal signatures of buried mines is not straightforward. Keywords: landmines, detection, thermal infrared, thermal signature, test facility. 1. INTRODUCTION Many sensors for landmine detection are affected by the water content, temperature, electrical conductivity and dielectric constant of the surrounding soil. The most important of these is soil water content since it directly influences the three other properties. Simunek et al. (2001) have conducted a modeling study to evaluate how soil texture and water affect the thermal signatures of land mines. They concluded that the maximum temperature difference between the soil surface above the mine and away from it, i.e. the strong thermal signature, depends in a complex manner on the thermal properties of the soil which depend on soil water and soil texture as well as the soil heat flux which changes with geographical location and time of the year. The strong thermal signature seems to appear in two six-hour intervals centered around 12:00 am and 12:00 pm but its exact time is very difficult to predict. To make matters worse, the weak thermal signatures frequently can also be found in these time intervals. Therefore, their modeling study indicates that the use of a single thermal sensor for instantaneous mine detection carries a high risk. On the other hand if a given area can be monitored constantly with a thermal sensor for twelve hours or longer a thermal signature may be detected if the signal to noise ratio of the mine-soil-sensor system allows so. Moreover, a thermal sensor can be useful in addition to other types of sensors like metal detector or ground penetrating radar in a multi-sensor fused mine detection system. DePersia et al. (1995) reported on thermal signatures in areas with land mines. Temperature differences between the soil surface above and away from the mine are attributed to differences in heat capacity between mine and soil as well as surface disturbance during mine burial. The major principle of thermal infrared (IR) sensors for mine detection is based on detecting localized temperature differences, apparent thermal contrast, introduced by the mines. The apparent thermal contrast also depends on background levels, and should be compared to the clutter contrast in order to derive the probability of detection of objects.
