There is interest in imaging ground target threats that are hidden in vegetation, straw grass, and foliage. In some instances, radar signals cannot penetrate through the “clutter.” Long wavelength sound waves might be capable of penetrating through the clutter so that the target can be acoustically detected and imaged. We study sound scattering by a canonical target “model disk” (aluminum, 4 inches diameter x 0.75 inch thick) in the presence of clutter. The clutter is modeled by a vertical hexagonal array of slender stainless steel rods that have an overall diameter D = 8 cm. The individual rods (diameter d = 0.089 cm, length L = 91 cm) are aligned and supported by two perforated thin (thickness = 1.8 mm) circular aluminum plates of diameter = 10 cm. Results for received backscattered tone burst echoes (at a frequency of 25.8 kHz) show that it is possible to detect the details of the target disk in the presence of a twodimensional circularly shaped cluster of rigid cylinders in air (representing clutter). The disk and “model” clutter targets were then taken out of the laboratory environment to an outdoor test site where the High Bandwidth Acoustic Detection System (HBADS) [developed by the US Army’s Night Vision and Electronic Sensors Directorate] performed an acoustic imaging experiment on the target-clutter and mechanical rigging apparatus. Using a linear frequency modulated LFM chirp pulse signal (2-15 kHz) driving a single speaker, echoes are detected by a 16 element microphone array while the HBADS vehicle is traveling ~ 1 m/s along a road. The strip-mapped synthetic aperture acoustic array SAA can image certain features of the apparatus.
High Bandwidth Acoustic Detection System (HBADS) is an emerging active acoustic sensor technology undergoing study by the US Army’s Night Vision and Electronic Sensors Directorate. Mounted on a commercial all-terrain type vehicle, it uses a single source pulse chirp while moving and a new array (two rows each containing eight microphones) mounted horizontally and oriented in a side scan mode. Experiments are performed with this synthetic aperture air acoustic (SAA) array to image canonical ground targets in clutter or foliage. A commercial audio speaker transmits a linear FM chirp having an effective frequency range of 2 kHz to 15 kHz. The system includes an inertial navigation system using two differential GPS antennas, an inertial measurement unit and a wheel coder. A web camera is mounted midway between the two horizontal microphone arrays and a meteorological unit acquires ambient, temperature, pressure and humidity information. A data acquisition system is central to the system’s operation, which is controlled by a laptop computer. Recent experiments include imaging canonical targets located on the ground in a grassy field and similar targets camouflaged by natural vegetation along the side of a road. A recent modification involves implementing SAA stripmap mode interferometry for computing the reflectance of targets placed along the ground. Typical strip map SAA parameters are chirp pulse = 10 or 40 ms, slant range resolution c/(2*BW) = 0.013 m, microphone diameter D = 0.022 m, azimuthal resolution (D/2) = 0.01, air sound speed c ≈ 340 m/s and maximum vehicle speed ≈ 2 m/s.
KEYWORDS: Acoustics, Transceivers, Foam, Prototyping, Imaging systems, Signal processing, Interference (communication), Target detection, General packet radio service, Signal to noise ratio
A novel quasi-monostatic system operating in a side-scan synthetic aperture acoustic (SAA) imaging mode is presented. This research project's objectives are to explore the military utility of outdoor continuous sound imaging of roadside foliage and target detection. The acoustic imaging method has several military relevant advantages such as being immune to RF jamming, superior spatial resolution as compared to 0.8-2.4 GHz ground penetrating radar (GPR), capable of standoff side and forward-looking scanning, and relatively low cost, weight and size when compared to GPR technologies. The prototype system's broadband 2-17 kHz LFM chirp transceiver is mounted on a manned all-terrain vehicle. Targets are positioned within the acoustic main beam at slant ranges of two to seven meters and on surfaces such as dirt, grass, gravel and weathered asphalt and with an intervening metallic chain link fence. Acoustic image reconstructions and signature plots result in means for literal interpretation and quantifiable analyses.
This work presents a set of measurements collected with a research prototype synthetic aperture acoustic (SAA) imaging
system. SAA imaging is an emerging technique that can serve as an inexpensive alternative or logical complement to
synthetic aperture radar (SAR). The SAA imaging system uses an acoustic transceiver (speaker and microphone) to
project acoustic radiation and record backscatter from a scene. The backscattered acoustic energy is used to generate
information about the location, morphology, and mechanical properties of various objects. SAA detection has a potential
advantage when compared to SAR in that non-metallic objects are not readily detectable with SAR. To demonstrate
basic capability of the approach with non-metallic objects, targets are placed in a simple, featureless scene. Nylon cords
of five diameters, ranging from 2 to 15 mm, and a joined pair of 3 mm fiber optic cables are placed in various
configurations on flat asphalt that is free of clutter. The measurements were made using a chirp with a bandwidth of 2-15
kHz. The recorded signal is reconstructed to form a two-dimensional image of the distribution of acoustic scatterers
within the scene. The goal of this study was to identify basic detectability characteristics for a range of sizes and
configurations of non-metallic cord. It is shown that for sufficiently small angles relative to the transceiver path, the
SAA approach creates adequate backscatter for detectability.
Synthetic aperture image reconstruction applied to outdoor acoustic recordings is presented. Acoustic imaging
is an alternate method having several military relevant advantages such as being immune to RF jamming, superior spatial
resolution, capable of standoff side and forward-looking scanning, and relatively low cost, weight and size when
compared to 0.5 - 3 GHz ground penetrating radar technologies. Synthetic aperture acoustic imaging is similar to
synthetic aperture radar, but more akin to synthetic aperture sonar technologies owing to the nature of longitudinal or
compressive wave propagation in the surrounding acoustic medium. The system's transceiver is a quasi mono-static
microphone and audio speaker pair mounted on a rail 5meters in length. Received data sampling rate is 80 kHz with a 2-
15 kHz Linear Frequency Modulated (LFM) chirp, with a pulse repetition frequency (PRF) of 10 Hz and an inter-pulse
period (IPP) of 50 milliseconds. Targets are positioned within the acoustic scene at slant range of two to ten meters on
grass, dirt or gravel surfaces, and with and without intervening metallic chain link fencing. Acoustic image
reconstruction results in means for literal interpretation and quantifiable analyses. A rudimentary technique
characterizes acoustic scatter at the ground surfaces. Targets within the acoustic scene are first digitally spotlighted and
further processed, providing frequency and aspect angle dependent signature information.
A novel outdoor synthetic aperture acoustic (SAA) system consists of a microphone and loudspeaker traveling along a
6.3-meter rail system. This is an extension from a prior indoor laboratory measurement system in which selected targets
were insonified while suspended in air. Here, the loudspeaker and microphone are aimed perpendicular to their direction
of travel along the rail. The area next to the rail is insonified and the microphone records the reflected acoustic signal,
while the travel of the transceiver along the rail creates a synthetic aperture allowing imaging of the scene. Ground
surfaces consisted of weathered asphalt and short grass. Several surface-laid objects were arranged on the ground for
SAA imaging. These included rocks, concrete masonry blocks, grout covered foam blocks; foliage obscured objects and
several spherical canonical targets such as a bowling ball, and plastic and metal spheres. The measured data are
processed and ground targets are further analyzed for characteristics and features amenable for discrimination. This
paper includes a description of the measurement system, target descriptions, synthetic aperture processing approach and
preliminary findings with respect to ground surface and target characteristics.
Using Laser Doppler vibrometry (LDV) to find buried land mines has been shown to have a high probability of detection
coupled with a low probability of false alarms. Previous work has shown that is it possible to scan a square meter in
20 seconds, but this method requires that discrete areas be scanned. This limits the use of LDVs for land mine detection
to a confirmation role. The current work at the University of Mississippi has been to explore ways to increase the speed
of scanning to allow the sensor to move down the road at speed. One approach has been to look at the feasibility of using
multiple beams to look at the same spot, time division multiplexing, in order to build a time history over small ground
segments as each beam passes over the spot. The composite velocity signature built from each beam will provide a long
enough time series to obtain the necessary frequency resolution.
A synthetic aperture acoustic approach is used as a standoff method to assess material properties of a typical
cinder block, referred to as a concrete masonry unit (CMU), and a variety of CMU surrogates. The objective is to
identify anomalies in CMU wall surfaces. The acoustic specular return and phase change across the blocks are the
fundamental measurements of interest. The CMU surrogates are created from commercially available closed cell
expanding foam. Results from three test articles are presented that show potentially exploitable differences in terms of
acoustic magnitude and acoustic phase response between the surrogates and typical CMUs. The test articles are; a
typical CMU, a foam block, and a foam block with an embedded steel object. All test articles are similar in size and
shape, and both foam blocks are covered in grout so that surface appearance closely matches that of a CMU. The results
show that each of the test articles has characteristics that may be used for discrimination and anomaly detection.
In this paper we look at the scattering of electromagnetic waves from thin wires. We propose a vehicle mounted search
radar system that rotates 360° about the vertical axis. Our wire of interest is lying on a lossy ground plane. It is generally
flat but has many bends, which gives it a vertical extent. The system is designed using a wire scattering simulator to
predict the response of a test wire to various illuminations. The simulator makes use of the Method of Moments technique
to predict the scattering of E&M waves in 3D. Several approximations make the tool fast and versatile. Among these is
the general assumption of the wire as a metal filament (with infinitesimal radius). To include a lossy ground plane we
suggest the use of the NEC2 simulator. In the development of this problem, we first look at scattering from a 3D thin
wire. The conclusion of the simulation phase of this work is that the cardinal flash or glint response of the wire must be
observed for the wire to be detectable. This response occurs when the wire is illuminated directly from the side. Because
this scenario occurs at an unknown location as the vehicle passes by the wire, our design suggests the use of a spinning
search radar. A brief experiment is performed using a search radar as a validation of concept. The observed glint response
is shown and suggestions are made for how a practical system could reduce false alarms. We conclude the paper with a
preferential configuration for a search radar suggested by simulation for this given application.
Remote acoustic or seismic forms of excitation for laser Doppler vibration landmine detection are low false alarm rate
detection strategies. A more recent approach now under investigation includes a direct mechanical excitation through a
prodder or probe. In this research, we report on simple laboratory measurements of the VS-1.6 landmine undergoing
direct mechanical excitation from a modified prodder while measuring the landmine's pressure plate vibrational
response with a scanning laser Doppler vibrometer. The direct mechanical excitation mechanism, located near the
prodding end of a rod, consists of a miniature piezoelectric stack actuator. We additionally compare direct excitation to
both acoustic and seismic methods in a large sandbox filled with dry sand. We show that for the landmine buried almost
flush, direct contact mechanical excitation compares favorably to both seismic and acoustic excitation responses for the
(0,1) mode of the pressure plate. We also observe additional features not previously seen in either seismic or acoustic
excitation.
Probe force and ground surface velocity measurements are obtained using laser Doppler vibrometry for one specific excitation contact point on the casing of the VS1.6 Antitank landmine for surface laid and buried scenarios. Probe contact force and ground velocity measurements were taken over a 1 KHz bandwidth (0 Hz to 1 KHz). Combined velocity magnitude and phase images are provided as laboratory results. The proposed excitation technique has the potential for significantly greater signal bandwidth and amplitude compared to remote acoustic and seismic excitation strategies.
KEYWORDS: Laser induced plasma spectroscopy, Land mines, Mining, Modal analysis, 3D modeling, Finite element methods, Sensors, Chemical elements, Signal processing, Systems modeling
The Italian VS 1.6 anti-tank landmine pressure plate was considered in a high fidelity finite element modal analysis using the ANSYS multi-physics application. The paper describes the approach taken to obtain material properties, namely density and Young's modulus, of the plastic components of the mine. It also discusses and provides illustrations of the three-dimensional finite element domain model with boundary conditions. The paper also describes the method by which the model was verified in a laboratory setting.
KEYWORDS: Sensors, Target detection, Land mines, Ground penetrating radar, Radar, General packet radio service, Signal detection, Detection and tracking algorithms, Target recognition, Data modeling
In this work we present an application of matched subspace detectors to the problem of target detection and identification using ground penetrating radar data. In particular we apply sets of matched subspace detector filter banks to data containing both anti-personnel and anti-tank targets as well as metallic and non-metallic clutter objects. Current results indicate the potential for robust target detection and identification but further improvements via subspace modeling and signal extraction/enhancement may also improve performance.
An overpass solution for antitank pressure-fused mines was developed and demonstrated for a teleoperated, four-wheeled experimental unmanned ground vehicle hosting a mine detection system using a downlooking ground-penetrating radar. The capability to overpass pressure-activated antitank mines is one way to protect the vehicle. The requirement was to make the vehicle overpass capable by giving it an average footprint pressure of no more than 5 psi using commercially available equipment and without requiring any vehicle modification. An overpass solution was developed and demonstrated using low-pressure, minimal casing rigidity tires that produce a uniformly low ground pressure and enable the vehicle to exert less than the minimum force required to activate the large majority of pressure-fused antitank mines. Overpass requirements are discussed in terms of antitank mine threats, pressure plate size, activation forces, and ground pressure distribution uniformity. A variable-load tire footprint pressure measurement system and laboratory were developed and laboratory evaluation of a number of tire candidates was completed. Laboratory results were demonstrated through field performance demos of the selected low-pressure tire. Results present the successful overpass of various threat representative antitank mines with the pressure plate elevations/exposures at various positions relative to local grade.
In this paper we present a multi-stage algorithm for target/clutter discrimination and target identification using the Niitek/Wichmann ground penetrating radar (GPR). To identify small subsets of GPR data for feature-processing, a pre-screening algorithm based on the 2-D lattice least mean squares (LMS) algorithm is used to flag locations of interest. Features of the measured GPR data at these flagged locations are then generated and pattern recognition techniques are used to identify targets using these feature sets. It has been observed that trained human subjects are often quite successful at discriminating targets from clutter. Some features are designed to take advantage of the visual aberrations that a human observer might use. Other features based on a variety of image and signal processing techniques are also considered. Results presented indicate improvements for feature-based processors over pre-screener algorithms.
KEYWORDS: Mining, General packet radio service, Soil science, Data modeling, Palladium, Performance modeling, Land mines, Metals, Sensors, Automatic target recognition
An empirical performance model for the Mine Hunter/Killer (MH/K) Ground Penetrating Radar (GPR) was developed and used to analyze the performance of this GPR as a function of soil type, soil moisture, mine casing and mine depth. The empirical modeling approach used can be modified to evaluate the performance of other GPRs if adequate data are collected. All of the data were reprocessed with the final MH/K automatic target recognition (ATR) algorithm so that performance variations due to environmental conditions could be characterized independently of ATR changes. The model estimates Probability of Detection (Pd) and False Alarm Rate (FAR) for buried mines as a function of ATR confidence, estimated soil moisture content (dry, moist or wet), mine casing (metal or plastic), burial depth (shallow or deep) and soil type (dirt or gravel). Time Domain Reflectometry (TDR) moisture probe measurements at one location augmented with qualitative observations of the soil conditions characterized the soil moisture content. The performance model was created from 52 alarm files collected at a temperate US Army test site over a total of 4 weeks during a 13-month period. The results show that for the MH/K GPR performance against plastic mines in dirt improves as soil moisture increases and performance in gravel is better overall than in dirt.
In this paper, a signal processing approach for wide-bandwidth ground-penetrating-radar imagery from Non-Intrusive Inspection Technology, Incorporated (NIITEK) vehicle-mounted landmine detection sensor is investigated. The approach consists of a sequence of processing steps, which include signal filtering, image enhancement and detection. Filtering strategies before detection aid in image visualization by reducing ground bounce, systematic effects and redundant signals. Post-filter image processing helps by enhancing landmine signatures in the NIITEK radar imagery. Study results from applying this signal processing approach are presented for test minefield lane data, which were collected during 2002 from an Army test site.
Reducing the false alarm rate of vehicular and hand-held mine detection systems has been a goal of most countermine detection programs. No thorough investigation into the causes of false alarms has been conducted to date. We present here an investigation into the sources of persistent ground-penetrating radar (GPR) false alarms that occurred during testing of a vehicular mine detection system. Data collected with this system was used to identify false alarms that persisted over several tests conducted over a two-year period over the same simulated roadway. A dig list was generated and several sites were excavated. Soil samples were collected at the sites and analyzed in the lab. The results of the excavation will be presented.
Estimating the temperature of bulk explosives in landmines is necessary for an optimally designed Nuclear Quadrupole Resonance explosive detection system, a technology that holds promise for mine detection system false alarm reduction. Pursuant to this objective it is necessary to study the heat conduction and temperature profiles of buried mines over diurnal cycles. Finite element models are constructed and a thermal analysis is performed for buried SIM-25 (landmine simulant) and VS 1.6 anti-tank landmine. The Ansys finite element software is used to create, to solve and to post-process the thermal models. Transient thermal analyses with various boundary conditions and simple soil models are performed. We report on the bulk explosive temperature, thermal flux and thermal gradients for these mine models over diurnal cycles.
KEYWORDS: General packet radio service, Land mines, Palladium, Mining, Detection and tracking algorithms, Sensors, Data fusion, Fusion energy, Calibration, Signal detection
This paper investigates the fusion of the confidence outputs of the Energy Based Processing (EBP) algorithm from the BAE Systems and the HMM GPR algorithm from the Univ. of Missouri to increase the performance of the Mine Hunter/Killer (MH/K) vehicle mounted landmine detection system. The EBP algorithm is based on the energy changes in GPR signal for detection. The HMM algorithm, on the other hand, is a feature based technique that relies on hyperbolic signatures to detect landmines. When fusing the detection confidences of the two algorithms properly, the performance is improved dramatically. The detection performance after fusion is demonstrated using data measured at a prepare test site during February and June 2000. Similar diagonal features used in HMM have been implemented and fused with EBP algorithm. Official offline scoring shows that the MH/K exit criteria of 92 percent Pd at 0.013/m2 FAR is met.
The Close-In Detector (CID) is the vehicle-mounted multi-sensor anti-tank landmine detection technology for the Army CECOM Night Vision Electronic Sensors Directorate (NVESD) Mine Hunter-Killer (MH/K) Program. The CID includes two down-looking sensor arrays: a 20-antenna ground-penetrating radar (GPR) and a 16-coil metal detector (MD). These arrays span 3-meters in front of a high mobility, multipurpose wheeled vehicle (HMMWV). The CID also includes a roof-mounted, forward looking infrared (FLIR) camera that images a trapezoidal area of the road ahead of the vehicle. Signals from each of the three sensors are processed separately to detect and localize objects of interest. Features of candidate objects are integrated in a processor that uses them to discriminates between anti-tank (AT) mines and clutter and produces a list of suspected mine locations which are passed to the neutralization subsystem of MH/K. This paper reviews the current design and performance of the CID based on field test results on dirt and gravel mine test lanes. Improvements in CID performance for probability of detection, false alarm rate, target positional accuracy and system rate of advance over the past year and a half that meet most of the program goals are described. Sensor performances are compared, and the effectiveness of six different sensor fusion approaches are measured and compared.
This report presents a summary of signal strength testing conducted with the metal detector (MD) subsystem of the Mine H/K (hunter/killer) vehicular mine detection system. An overview of the operational characteristics of the MD subsystem, the VMV16, is provided. Tests are described that assess the variation in sensitivity across the MD coil array. Absolute sensitivity measurements of the MD array are also presented. Results presented show that the array has sufficient sensitivity to detect low metal (LM) mines provided the mines are not located further than 3.5 inches from the plane of array. Laboratory experiments indicate that saturation and a limited temporal sampling window severely restrict any opportunity for discrimination based on eddy current decay predictions/comparisions.
KEYWORDS: Sensors, Neural networks, Land mines, General packet radio service, Metals, Mining, Infrared sensors, Data fusion, Infrared signatures, Antennas
The MH/K) Close in Detector (CID) system employs ground penetrating radar (GPR), forward looking IR and metal detectors that are individually and collectively processed to generate automatic target detections. The detection preprocessing is initially being accomplished on a sensor by sensor basis. For the IR sensor, we apply digital filtering techniques and morphology to detect the mines and a separate filter to characterize the background level. For preprocessing the GPR returns, we apply an inverse Fourier transform to the complex frequency return signal to obtain depth information and apply digital filtering techniques to remove fixed pattern noise and provide contrast enhancement. Metal detector returns are preprocessed using a distance measure of the return compared with the averaged background. A representative data set is extracted from the preprocessed data for each of the sensor types. Other MH/K team efforts for ATR and fusion development include TRW, BAE and Sandia National Laboratories.
The Close-in Detection (CID) System is the vehicle-mounted multisensor landmine detection system for the Army CECOM Night Vision Electronic Sensors Directorate (NVESD) Mine Hunter/Killer (MH/K) Program. The CID System is being developed by BAE Systems in San Diego, CA. TRW Systems and Information Technology Group in Arlington, VA and a team of specialists for ERIM, E-OIR, SNL, and APL/JHU support NVESD in the development, analysis and testing of the CID and associated signal and data processing. The CID System includes tow down-looking sensor arrays: a ground- penetrating radar (GPR) array, and a set of Electro-Magnetic Induction (EMI) coils for metal detection. These arrays span a 3-meter wide swath in front of a high mobility, multipurpose wheeled vehicle. The system also includes a forward looking IR imaging system mounted on the roof of the vehicle and covering a swath of the road ahead of the vehicle. Signals from each sensor are processed separately to detect and localize objects of interest. Features of candidate objects are integrated in a processor that uses them to discriminates between anti-tank miens and clutter. Mine locations are passed to the neutralization subsystem of MH/K. This paper reviews the design of the sensors and signal processing of the CID system and gives examples and analysis of recent test results at the NVESD mine lanes. The strengths and weaknesses of each sensor are discussed, and the application of multisensor fusion is illustrated.
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