Buried Landmines Research Articles

Acoustic Detection of Buried Landmines Using Pulsed ESPI

Acoustic methods of landmine detection have demonstrated promising results in detecting buried landmines in laboratory and field tests. They are based on generation of vibrations of the ground and measurement of the vibration response of the ground over the area of interest. A buried landmine can be detected by analyzing spatial distribution of the ground vibration. Reliable detection of mines requires fast measurement of vibration with high spatial resolution. This work studies the application of a pulsed electronic speckle pattern interferometer (ESPI) for the vibration measurement of the ground surface in acoustic landmine detection. Experimental results are presented from laboratory experiments. The effect of the vibration of unconsolidated soil on the speckle decorrelation is discussed. Results show that pulse ESPI can create a spatial map of vibrating ground in a time equal to or shorter than a half a period of vibration and have the ability to detect buried landmines.

Multi-beam laser Doppler vibrometer for landmine detection

The method of buried landmine detection based on using elastic waves in the ground and a laser Doppler vibrometer (LDV) as a vibration sensor has shown excellent performance in field tests. To increase the speed of measurements, a multi-beam laser Doppler vibrometer (MB-LDV) was developed. The system is based on a heterodyne interferometer and is capable of simultaneously measuring the vibration of the ground at 16 points over a span of 1 m with a velocity resolution of less than 1 µm/s. Both digital in-phase and quadrature (I&Q) and analog phase-locked loop (PLL) demodulation have been used for signal processing. The MB-LDV can create a velocity image of the ground surface either in "stop-and-stare" mode or in a continuously scanning mode. The continuously scanning operation results in an increased velocity noise floor due to speckle noise. The speckle noise floor increases with the increase of the speed of the laser beam and can degrade the velocity image of a mine. To overcome the effects of speckle noise, the excitation source must provide a ground vibration velocity higher than the velocity noise floor of the vibrometer. The MB-LDV has been tested at landmine test lanes and shows the ability to detect buried landmine within a one-square-meter area in a time of less than 20 s.

Clutter reduction in GPR measurements for detecting shallow buried landmines: a Colombian case study

ABSTRACTDetection of land‐mines from ground‐penetrating radar data is a challenging task demanding accurate and useful filtering techniques to reduce soil‐surface and antenna reflections, which obscure the landmine response. In this paper, we apply and adapt a recently proposed filtering approach to enhance the detection of shallow buried anti‐personnel land‐mines from data acquired in typical mine‐affected soils in Colombia. The methodology combines a radar‐antenna‐subsurface model with phase‐shift migration to filter out antenna and soil‐surface effects from off‐ground monostatic radar two‐dimensional data. Firstly, antenna multiple reflections are removed using linear transfer functions. Secondly, simulated Green's functions accounting for the surface reflection are subtracted. These functions are derived using the relative dielectric permittivity of the surface, which is estimated by full‐wave inversion of the radar signal for measurements taken in local land‐mine‐free areas. Finally, the antenna radiation pattern effect is filtered out by performing phase‐shift migration, and information about size and shape is extracted. Data are acquired using a hand‐held vector network analyser connected to an off‐ground monostatic horn antenna. Typical Colombian targets such as low‐metallic anti‐personnel land‐mines and low‐ and non‐metallic improvised explosive devices are used. Results prove that the proposed technique effectively reduces clutter under non‐controlled conditions and yields target features that are useful for detection of these land‐mines.

Heat and Mass Transfer in Moist Soil, Part II. Application to Predicting Thermal Signatures of Buried Landmines

The finite-volume-based numerical procedure for unsteady heat and moisture transport in soil developed in a companion article [1] is used to study the surface thermal signature of buried landmines in moist soil. The effect of soil type, soil moisture content, mine type, and mine burial depth on the thermal contrast at the soil surface is analyzed over a diurnal cycle. Predictions are presented in the form of spatial and temporal profiles of temperature, matric potential, and surface thermal contrast. Results reveal that the thermal contrast at the surface becomes weaker as the burial depth increases. For shallowly buried mines (i.e., buried at a depth of less than 2 cm), there is an optimum matric potential or moisture content value that maximizes the thermal contrast at the soil surface, with this value being highly dependent on the type of soil and/or mine. Varying the mine burial depth and/or soil moisture content changes the time of the day at which this maximum thermal contrast occurs.

Fluorescence of Aromatic Amines and Their Fluorescamine Derivatives for Detection of Explosive Vapors

Nitroaromatics (such as dinitrotoluene, trinitrotoluene, and nitrobenzene) found in explosive vapors from buried landmines can be reduced to aminoaromatics by a novel process involving Pd metal nanocatalysts prepared in supercritical fluid carbon dioxide and supported on multi-walled carbon nanotubes. These aminoaromatics are fluorescent and, if desired, the fluorescence yield can be increased and the fluorescence maxima shifted further toward the red by reaction with appropriate derivatizing agents such as fluorescamine. Corrected spectra for these chemicals and their derivatives are included. Subpicomolar detection limits have already been achieved using a laboratory spectrofluorometer with a 150 W Xe arc lamp. Using lasers as excitation sources, this approach has the potential for developing a field sensor competitive with other methods currently used for detecting explosive vapors from land mines.

Electrical Impedance Tomographic Imaging of Buried Landmines

A prototype confirmation landmine detector, based on electrical impedancetomography (EIT), which can operate under realistic environmental conditions, has been developed. Laboratory and field experiments demonstrated that it is possible to reliably reconstruct, on the scale of the electrode spacing (ES) (in width and depth), conductivity perturbations due to a shallow buried antitank mine or a similar object in a variety of soils (black earth, clay, sand) down to depths equal to the dimensions of the object (1-1.5 ES, equivalent to 14-21 cm for a 64-electrode 1 m times 1 m array). These represent the first EIT images of real landmines computed from measured data. Occasional problems were encountered with the electrical contact in very dry soils, with excessive insertion pressure being required for reliable electrode contact. However, poor contacts could be detected, and the offending probe was either reinserted or compensation was applied. A matched filter detection algorithm based on a replica of the object of interest was developed and shown to effectively reduce the false alarm rate of the detector. EIT is especially suited for wet lands and underwater, where other mine detectors perform poorly. Experiments in a water-and sediment-filled tank have demonstrated that detection of minelike objects in such an environment with a submerged array is feasible. These experiments represent the first EIT measurements of targets using an electrode array submerged underwater. EIT may also have an application in locating intact mines in the berms formed by mine-clearing equipment. The EIT sensor head could be made cheaply enough to be disposable and remotely inserted to improve safety

Detection of buried landmine with X-ray backscatter technique

We describe a continuously operating scanning X-ray imaging system developed for landmine detection based on a backscatter X-ray principle, thus detection is done from the same side as the source. The source operates at 120 kV p and 3 mA. To study the physics of Compton X-ray backscattering, the photon transport factor, backscatter factor (BSF) and backscatter probability (BSP) were simulated using Monte-Carlo calculations using the generalized particle transport program MCNP. Based on the Monte-Carlo analyses results, a mine detecting system has been designed. It potentially has a low false alarm rate and a high detection probability, and a direct imaging facility.

Effects of soil electromagnetic properties on metal detectors

This paper presents an analysis, based on existing work in geophysics and nondestructive testing, of the effects of soil electromagnetic properties on the functioning of metal detectors widely used to detect buried landmines. The host soil is modeled as a half-space having real and frequency-independent electrical conductivity but frequency-dependent complex magnetic susceptibility. The analysis technique has been applied to three examples of soil of practical importance, namely, nonconducting soil with frequency-independent susceptibility, nonconducting soil with frequency-dependent susceptibility, and nonmagnetic soil with constant conductivity. Simplifications are made to clearly explain a number of previous field and experimental observations, for example, the greater influence of magnetic properties than of electrical conductivity on the performance of metal detectors. Results also show that soil magnetic properties affect continuous wave and pulsed-induction detectors differently. The effect that electrical conductivity and magnetic susceptibility of the host soil have on the signal produced by a target is investigated by computing the response of a buried small metallic sphere. Computations show that in some cases, which could represent practical landmine detection scenarios, the signal from the soil can dominate that due to the target, making it hard to detect the target. Further, it is shown that magnetic soil can alter a target's spectral response, which implies that, contrary to present practice, object identification techniques should take into account the electromagnetic parameters of the host medium.

Nonlinear acoustic detection of buried landmines: A tribute to Joe Blue

As a graduate student at Brown University (∼1978), this researcher was very fortunate to have met Joe Blue at Acoustical Society meetings. As I had little knowledge of the members in the society and an extremely limited grasp of the practical technology behind nonlinear acoustics, Joe was extremely friendly and took the time to answer a long list of questions about nonlinear underwater transducer designs with applications to the parametric array [Muir, T.G. & Blue, J.E. ‘‘Experiments on the acoustic modulation of large-amplitude waves,’’ J. Acoust. Soc. Am. 46, 227–232 (1969)]. This influenced this researcher’s Ph.D. thesis involving experiments on the scattering of sound by sound in the presence of turbulence. Recently, experiments on the nonlinear acoustic detection of buried landmines [Korman, M.S. & Sabatier, J.M., ‘‘Nonlinear acoustic techniques for landmine detection,’’ J. Acoust. Soc. Am. 116, 3354–3369 (2004)] has brought some attention to understanding the difference between classical and nonclassical nonlinearity. As a tribute to Joe Blue, the latest results will be presented involving the connections to mesoscopic nonlinear elasticity and slow dynamics in nonlinear buried landmine detection. Here, tuning curve behavior of the soil-surface vibration over a landmine exhibits a linear decrease in resonant frequency with increasing amplitude. Two-tone test excitation reveals a rich spectrum of combination frequency components useful in detection schemes.

An abrupt change detection algorithm for buried landmines localization

Ground-penetrating radars (GPRs) are very promising sensors for landmine detection as they are capable of detecting landmines with low metal contents. GPRs deliver so-called Bscan data which are, roughly, vertical slice images of the ground. However, due to the high dielectric permittivity contrast at the air-ground interface, a strong response is recorded at early time by GPRs. This response is the main component of the so-called clutter noise and it blurs the responses of landmines buried at shallow depths. The landmine detection task is therefore quite difficult. This paper proposes a new method for automated detection and localization of buried objects from Bscan records. A support vector machine algorithm for online abrupt change detection is implemented and proves to be efficient in detecting buried landmines from Bscan data. The proposed procedure performance is evaluated using simulated and real data.

Structural vibrations of buried land mines

Buried landmines exhibit complex structural vibrations, which are dependent on interaction between soil and mines as well as on their respective properties. This paper presents experimental and theoretical studies of multimodal vibrations of buried mines and discusses the effects of burial depth and soil properties on dynamics of the soil-mine system. The two-dimensional model of the soil-mine system that accounts for soil-coupled mine’s multiple vibration modes and spatial distribution of vibrations over the soil surface is introduced. The model was tested using experiments with the plastic mine simulant. The study reveals that the soil shear stiffness is one of the key governing parameters determining the resonance vibration frequency and the amplitude of the soil-mine system. Burial depth, soil moisture, and consolidation are among factors leading to the increase of the soil shear stiffness, therefore effectively influencing modal vibrations of buried mines.

Numerical and Experimental Investigation of Thermal Signatures of Buried Landmines in Dry Soil

This paper reports a numerical and experimental investigation conducted to study the thermal signature of buried landmines on soil surface. A finite-volume-based numerical model was developed to solve the unsteady three-dimensional heat transport equation in dry homogeneous soil with a buried mine. Numerical predictions of soil thermal response were validated by comparison with published analytical and numerical values in addition to data obtained experimentally. Experiments were performed inside an environmental chamber and soil temperatures were measured during cooling, using two measurement techniques, after exposing the soil surface to a radiant heat flux for a specified period. In the first technique, the temporal variation of the surface and internal soil temperatures were recorded using thermocouples. In the second technique, the soil surface temperature was measured using an infrared camera that revealed the thermal signature of the mine. The transient temperature profiles generated numerically agreed with measurements, and the difference between predicted and measured values was less than 0.3°C at both the soil surface and in depth. The accurate matching of numerical and IR images at the surfaces was found to strongly depend on the use of a smaller soil thermal conductivity at the surface than at greater depths. The numerical model was used to predict the dependence of the peak thermal contrast on time, depth, and heating period. The thermographic analysis, when combined with numerical predictions, holds promise as a method for detecting shallowly buried land mines.

Nonlinear acoustic landmine detection: Comparison of ‘‘off target’’ soil background and ‘‘on target’’ soil-mine nonlinear effects

When airborne sound at two primary tones, f1, f2 (closely spaced near a resonance) excites the soil surface over a buried landmine, soil wave motion interacts with the landmine generating a scattered surface profile which can be measured over the ‘‘target.’’ Profiles at f1, f2, and f1−(f2−f1), f2+(f2−f1), 2f1−(f2−f1), f1+f2 and 2f2+(f2−f1) (among others) are measured for a VS 1.6 plastic, inert, anti-tank landmine, buried at 3.6 cm in sifted loess soil. It is observed that the ‘‘on target’’ to ‘‘off target’’ contrast ratio for the sum frequency component can be ∼20 dB higher than for either primary. The vibration interaction between the top-plate interface of a buried plastic landmine and the soil above it appears to exhibit many characteristics of the mesoscopic/nanoscale nonlinear effects that are observed in geomaterials like sandstone. Near resonance, the bending (softening) of a family of increasing amplitude tuning curves, involving the vibration over the landmine, exhibits a linear relationship between the peak particle velocity and corresponding frequency. Tuning curve experiments along with two-tone tests are performed both on and off the mine in an effort to understand the nonlinearities in each case. [Work supported by U.S. Army RDECOM CERDEC, NVESD.]

Thermal detection of buried landmines by local heating

A new concept for buried antipersonnel mine (APM) detection is proposed. The detection system is based on a focused heat source and a contactless thermometer mounted on a suspended carriage scanning the ground surface. Presence of heat diffusivity anomalies (mine candidates) is assessed from anomalies in the surface temperature measured after the local heating. After describing the structure of the proposed system, and the physical functioning principles, we discuss a case study, based on numerical simulations, which proves the feasibility of the device. Main advantages of the system proposed are the simplicity of the equipment (that is cheap to realize, and easy to use, maintain and repair), and power efficiency.

Strength of landmine signatures under different soil conditions: implications for sensor fusion

Most sensors for the detection of buried landmines are influenced by the properties of the soil that surrounds the mine. The temporal and spatial variability in soil properties accounts for a significant part of the detection uncertainty that is associated with most sensors. In particular, most sensor types (e.g. ground-penetrating radar, thermal infrared cameras, and chemical sniffers) are affected by the water content of the soil. However, each sensor type reacts in its own way to variations in soil water content and other soil properties. The resulting variation in sensor performance has serious implications for sensor fusion operations. We show how knowledge of soil physics can contribute to a better understanding of sensor performance and can lead to improved data fusion.

Detection of buried landmines and hidden explosives using neutron, X-ray and gamma-ray probes

Detection of buried landmines and hidden explosives using neutron, X-ray and gamma-ray probes

A Method for Detecting Shallowly Buried Landmines Using Sequential GPR Data

A method for detecting shallowly buried landmines using sequential ground penetrating radar (GPR) data is presented. After removing a dominant coherent component arising from the ground surface reflection from the GPR data, three kinds of target features related to wave correlation, energy ratio, and signal arrival time are extracted. Since the detection problem treated here is reduced to a binary hypothesis test, an approach based on a likelihood ratio test is employed as a detection algorithm. In order to check the detection performance, a Monte Carlo simulation is carried out for data generated by a two-dimensional finite-difference time domain (FDTD) method. Results given in the form of receiver operating characteristic (ROC) curves show that good detection performance is obtained even for landmines buried at shallow depths under rough ground surfaces, where the responses from the landmines and that from the ground surface overlap in time.

Nonlinear acoustic experiments involving landmine detection: Connections with mesoscopic elasticity and slow dynamics in geomaterials, Part II

In nonlinear acoustic detection, airborne sound at two primary tones, f1, f2 (chosen several Hz apart from resonance) insonifies the soil surface over a buried landmine, and due to soil wave interactions with the landmine, a scattered surface profile can be measured by an LDV. Profiles at f1, f2, f1−(f2−f1) and f2+(f2−f1) exhibit a single peak while profiles at 2f1−(f2−f1), f1+f2 and 2f2+(f2−f1) are attributed to higher order mode shapes. The lowest resonant frequency for a VS 1.6 plastic, inert, anti-tank landmine, buried at 3.6 cm deep is ∼125 Hz. The ‘‘on target’’ to ‘‘off target’’ contrast ratio, for some of the nonlinearly generated combination tones, is roughly 15–20 dB higher compared to either primary component. Near resonance, the bending (softening) of a family of increasing amplitude tuning curves, involving the surface vibration over the landmine, exhibits a linear relationship between the peak particle velocity and corresponding frequency. The tuning curves exhibit hysteresis effects. Landmine-soil vibrations exhibit similar characteristics to nonlinear mesoscopic/nanoscale effects that are observed in geomaterials like rocks or granular materials. Nonlinear mechanisms of soil and the soil interacting with the top-plate of the mine case are compared. [Work supported by U.S. Army RDECOM CERDEC, NVESD.]

Time-dependent finite-element model for optimizing source array element position and excitation for a seismic sonar for buried mine detection

A three-dimensional (3-D) continuum mechanics approach to the development of a time-dependent finite-element model for optimizing the position and excitation of source array elements for use in a seismic sonar to detect buried landmines is presented. Mathematical formulation of the problem consists of the coupling of a system of linear, second order, partial differential equations and related boundary conditions into one single wave equation, from which a composite elastic finite element is derived. The hp-adaptive finite-element kernel, ProPHLEX [Altair Engineering, Inc., McKinney, TX], is used to perform the numerical computations. The radiation characteristics of a discrete number of transient seismic sources are analyzed in a linear, isotropic, homogeneous half-space. Results for radial and vertical radiation fields, and for radiated Rayleigh wave strength will be presented for various source configurations. Particular attention will be paid to those configurations which maximize the radiation of unidirectional Rayleigh waves, while suppressing the radiation of unwanted body waves.

Non-intrusive ground-contacting vibrometer for acoustic/ seismic landmine detection

The detection of buried landmines using seismic waves and full wave-field measurements has been demonstrated. The technique requires a sensor that is non-intrusive with sufficient fidelity, reproducibility, and noise immunity for imaging processes. This has been accomplished in the past with non-contact techniques. For reasons of cost and scalability in large arrays, ground-contacting sensors are currently of interest as an alternative to these. A ground-contacting sensor configuration was studied in which an accelerometer was coupled to the ground through a viscoelastic layer with a bias force provided by a soft coil spring. This sensor was found to meet the noise, fidelity, and reproducibility requirements of a seismic landmine detection system operating in a laboratory experimental model. The fidelity of this sensor was found to vary with the bias force because of the nonlinear stiffness of the soil surrogate in the model. This dependence was sufficiently weak that no feedback of the bias force was necessary to reproducibly couple the sensor over a flat surface. The sensor offers the potential benefit of information that was not available from non-contact measurements regarding the in-plane motion of the soil surface. This data may provide additional cues for the detection of buried mines. [Work supported by ONR.]