James D. Habersat

Propagation velocity uncertainty on GPR SAR processing

To detect buried landmines, Planning Systems Incorporated (PSI) has developed a ground-penetrating synthetic aperture radar (GPSAR) system. Since the electromagnetic wave propagation velocity in the soil depends on many factors, velocity uncertainty is inevitable. However, we have observed that, unlike conventional airborne/spaceborne synthetic aperture radar (SAR) systems, the PSI GPSAR system is very robust against the velocity uncertainty under mild conditions. Theoretical analysis is provided to explain this observation. Although our discussion is based on the PSI GPSAR system, it applies to other GPR-based (ground-penetrating radar) landmine detection systems as well.

Elimination of leakage and ground-bounce effects in ground-penetrating radar data

We address the problem of removing specular ground surface reflections and leakage/cross-talk from downward looking stepped frequency ground-penetrating radar (GPR) data. A new model for the ground-bounce and the leakage/cross-talk is introduced. An algorithm that jointly estimates these effects from collected data is presented. The algorithm has the sound foundation of a nonlinear least squares (LS) fit to the presented model. The minimization is performed in a cyclic manner where one step is a linear LS minimization and the other step is a non-linear LS minimization where the optimum can efficiently be found using, e.g., the chirp-transform algorithm. The results after applying the algorithm to measured GPR data, collected at a US army test range, are also shown.

Removal of surface returns in ground-penetrating radar data

Techniques using ground-penetrating radar (GPR) for the detection of targets such as abandoned landmines or unexploded ordnance (UXO) buried under the ground surface continue to receive considerable attention especially in the area of signal processing. In this paper we consider the problem of eliminating the so-called ground-bounce effect, which is due to the specular ground surface reflections of the radar signal. The ground-bounce returns are often significantly stronger than the reflection from a target and pose a challenging problem. Existing techniques commonly assume that the ground response is constant as the radar equipment moves along a track. By using measured data, we show that this is, for several reasons, an unrealistic assumption. Instead, we consider a semi-parametric model for the ground-bounce that is in better agreement with observed data. Furthermore, we show how this model can be used to derive an accurate and robust but yet conceptually simple algorithm for the removal of the ground return. We demonstrate our technique using data recorded by an ultra-wideband GPR on a U.S. Army test range.

Development of a robust algorithm for detection of mine targets in image data from electro-optic and acoustic sensors

Current minefield detection research indicates that operationally no single sensor technology will likely be capable of detecting mines/minefields in a real-time manner and at a performance level suitable for a forward maneuver unit. Minefield detection involves a particularly wide range of operating scenarios and environmental conditions, which requires deployment of complementary sensor suites. We have focused, therefore, on the development of a computationally efficient and robust detection algorithm that exploits robust image processing techniques centered on meaningful target feature sets applicable to a variety of imaging sensors. This paper presents the detection technique, emphasizing its robust architecture, and provides performance results for image data generated by complementary sensors. The paper also briefly discusses the application of this detector as a component of fusion architectures for processing returns form diverse imaging sensors, including multi-channel image data from disparate sensors.

NVESD mine lane facility

The NVESD Mine Lane Facility has recently undergone an extensive renovation. It now consists of an indoor, dry lane portion, a greenhouse portion with moisture-controlled lanes, a control room, and two outdoor lanes. The indoor structure contains six mine lanes, each approximately 2.5m (width) × 1.2m (depth) × 33m(length). These lanes contain six different soil types: magnetite/sand, silt, crusher run gravel (bluestone gravel), bank run gravel (tan gravel), red clay, and white sand. An automated trolley system is used for mounting the various mine detection systems and sensors under test. Data acquisition and data logging is fully automated. The greenhouse structure was added to provide moisture controlled lanes for measuring the effect of moisture on sensor effectiveness. A gantry type crane was installed to permit remotely controlled positioning of a sensor package over any portion of the greenhouse lanes at elevations from ground level up to 5m without shadowing the target area. The roof of the greenhouse is motorized, and can be rolled back to allow full solar loading. A control room overlooking the lanes is complete with recording and monitoring devices and contains controls to operate the trolleys. A facility overview is presented and typical results from recent data collection exercises are presented.

Adaptive ground bounce removal

For downward looking GPR landmine detection systems, the return from the ground surface, i.e., the ground bounce, often surpasses the actual mine return and makes it almost impossible to detect the landmines, especially the buried plastic landmines. The ground bounce is difficult to remove due to the roughness of the ground surface and/or the changing soil conditions. In this paper, a robust and efficient ground bounce removal algorithm, referred to as ASaS (Adaptive Shift and Scale), is presented. ASaS takes into account the variations of the ground bounce by adaptively selecting a reference ground bounce. The shifted and scaled version of the reference ground bounce is used as the estimate of the ground bounce in the current scan. Two adaptive reference selection schemes for ASaS are given and compared with each other. Experimental results based on the data collected by the PSI GPSAR system are used to demonstrate the effectiveness of the adaptive schemes.

SAR processing for GPSAR systems

Planning Systems Incorporated (PSI) has developed a promising Ground Penetrating Synthetic Aperture Radar (GPSAR) system to detect buried landmines. GPSAR can be used to generate three-dimensional (3-D) mine images. It has been shown that the SAR processing in the PSI GPSAR system can greatly improve the image quality and hence the mine (especially plastic mine) detection performance. In this paper, two special issues on SAR processing for the PSI system are addressed. One issue is the analysis of the effect of the underground electromagnetic (EM) wave propagation velocity uncertainty on SAR processing and the other is channel mismatch on SAR processing. Since the EM wave propagation velocity in the soil depends on many factors and changes from one location to another, velocity uncertainty is inevitable. However, we have found that the PSI GPSAR system is very robust against the velocity uncertainty. More specifically, velocity uncertainty does not defocus the image but only scales the image along the depth dimension, and hence will not affect the mine detection performance. Another issue is how to select a good SAR processing scheme for the PSI system. Because the radar footprint is 2-D (along-track and cross-track dimensions), 2-D SAR processing may be used. However, the effectiveness of the 2-D SAR processing depends on the coherence of the radar antenna system. Moreover, the computational expense of the 2-D SAR processing is much higher than that of the 1-D SAR processing (along-track dimension only). We have found that due to the channel mismatch of the PSI system, the 2-D SAR processing does not greatly improve the quality of the SAR images when compared with 1-D SAR processing. Hence, without proper antenna calibration, the computationally more efficient 1-D SAR processing may be preferred for the PSI system.

Eyesafe laser-illuminated tripwire (ELIT) detector

The technical issues of a standoff electro-optic tripwire detector are discussed. Significant advances in short-wave infrared (SWIR) laser diodes and InGaAs detector technologies have made it possible for the demonstration of a passive and active eyesafe (1.5 micron) laser illuminated tripwire (ELIT) detector. The demonstrated system utilizes COTS laser diodes and cameras. The Hough Transform was used for the detection of tripwires in images. System trade-offs are discussed and images are shown.

Laser neutralization of surface and buried munitions

In recent years NVESD has been investigating laser-based neutralization of buried mines and minelike targets. This paper covers the most recent efforts in this area. A field-test was conducted to demonstrate the state-of-the-art capability for standoff laser neutralization of surface and buried mines. The neutralization laser is a Ytterbium fiber laser with a nominal power output of 10 kW and a beam quality of M2 ≈ 1.8 at maximum power. Test trials were conducted at a standoff range of 50 meters with a 20° angle of attack. The laser was focused to a submillimeter spot using a Cassegrain telescope with a 12.5 inch diameter primary mirror. The targets were 105 mm artillery rounds with a composition B explosive fill. Three types of overburden were studied: sand, soil, and gravel. Laser neutralization capability was demonstrated under these conditions for live rounds buried under 7 cm of dry sand, 4 cm of soil, and 2 cm of gravel.

Acoustic technology for land mine detection: past tests, present requirements, and future concepts

A recent blind test and two data collections at the US Army mien test lanes at Ft AP Hill have demonstrated the great potential for the use of acoustic technology to detect buried land mines. The acoustic system built by the University of Mississippi under a contract with the Night Vision and Electronic Sensors Directorate demonstrated a very high probability of detection, a very low false alarm rate, extremely good location accuracy, and significant standoff potential. A large number of papers are being presented at this conference that deal with various specific aspects of this program. This paper will present a broad but technical overview of this program. We will describe the capabilities of this approach and the areas in which improvements are being addressed. We will discuss briefly fusion with additional sensors, which will illustrate the manner in which acoustic technology can be integrate with other sensor to form a viable and robust mine detection system. We will present the present Army requirements and operational concepts that would meet these requirements.