Steven S. Bishop

Feature-based processing of prescreener-generated alarms for performance improvements in target identification using the NIITEK ground-penetrating radar system

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.

Investigation into the sources of persistent ground-penetrating radar false alarms: data collection, excavation, and analysis

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.

Processing of GPR data from NIITEK landmine detection system

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.

Demultiplexing multiple-beam laser Doppler vibrometry for continuous scanning

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.

Synthetic aperture acoustic measurements of stationary suspended cinderblock and surrogate substitutes

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.

Synthetic aperture acoustic imaging of non-metallic cords

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.

Direct mechanical landmine excitation with scanner laser Doppler vibrometer surface measurements

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 landmines 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.

Fusion of energy-based processing and HMM GPR algorithms for the mine hunter/killer program

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.

Improved close-in detection for the mine hunter/killer system

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.

Synthetic aperture acoustic imaging of canonical targets with a 2-15 kHz linear FM chirp

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 systems 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.