A noncoherent radar system approach for through-the-wall imaging
20 May 2005-Vol. 5778, pp 196-207
TL;DR: The proposed noncoherent through-the-wall radar system approach, based on trilateration technique, is presented and the results show that the radar is able to detect and locate multiple targets behind walls.
Abstract: A noncoherent through-the-wall radar system approach, based on trilateration technique, is presented. This approach involves multiple independent monostatic radar units and as such, provides flexibility in positioning the units with various stand-off distances and inter-element spacing. We demonstrate the proposed noncoherent system approach in an indoor environment using both simulated and real data. The results show that the radar is able to detect and locate multiple targets behind walls.
Citations
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TL;DR: A technique using two or more standoff distances of the imaging system from the wall is proposed for application under wall parameter ambiguities, and extensive simulation examples demonstrate their effectiveness.
Abstract: In through-the-wall imaging, errors in wall parameters cause targets to be imaged away from their true positions. The displacement in target locations depend on the accuracy of the estimates of the wall parameters as well as the target position relative to the antenna array. A technique using two or more standoff distances of the imaging system from the wall is proposed for application under wall parameter ambiguities. Two different imaging schemes can then be applied to correct for errors in wall characteristics. The first scheme relies on forming target displacement trajectories, each corresponding to a different standoff distance, and assuming different values of wall thickness and dielectric constant. The target position is then determined as the trajectories crossover point. In the second scheme, an image sequence is generated. Each specific image in this sequence is obtained by summing those corresponding to different standoff distances, but with the same assumed wall parameters. An imaging-focusing metric can then be adopted to determine the target position. The paper analyzes the above two schemes and provides extensive simulation examples demonstrating their effectiveness
167 citations
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TL;DR: In this paper, a technique for target location estimation in through-the-wall radar imaging applications is presented, which corrects for the shifts in target positions due to ambiguities in the wall thickness and dielectric constant.
Abstract: A technique for target location estimation in through-the-wall radar imaging applications is presented. The algorithm corrects for the shifts in target positions due to ambiguities in the wall thickness and dielectric constant. We consider uniform walls and perform imaging using wideband beamforming, with the antennas placed against the wall. Behind-the-wall images are obtained using different structures of transmit and receive arrays. For each array structure, a trajectory of the shifts in the target locations is generated assuming different wall parameters. The target position is estimated as the intersection of the corresponding trajectories. The paper shows that for unknown wall thickness or dielectric constant, the point of intersection is the true target position. In the case when both parameters are unknown, the estimated target location is in close proximity to the target true position. It is demonstrated that the performance of the proposed technique is rather insensitive to the target location behind the wall and to various array structures.
117 citations
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TL;DR: This paper enables joint wall clutter mitigation and CS application using a reduced set of spatial-frequency observations in stepped frequency radar platforms and demonstrates that wall mitigation techniques, such as spatial filtering and subspace projection, can proceed using fewer measurements.
Abstract: Compressive sensing (CS) for urban operations and through-the-wall radar imaging has been shown to be successful in fast data acquisition and moving target localizations. The research in this area thus far has assumed effective removal of wall electromagnetic backscatterings prior to CS application. Wall clutter mitigation can be achieved using full data volume which is, however, in contradiction with the underlying premise of CS. In this paper, we enable joint wall clutter mitigation and CS application using a reduced set of spatial-frequency observations in stepped frequency radar platforms. Specifically, we demonstrate that wall mitigation techniques, such as spatial filtering and subspace projection, can proceed using fewer measurements. We consider both cases of having the same reduced set of frequencies at each of the available antenna locations and also when different frequency measurements are employed at different antenna locations. The latter casts a more challenging problem, as it is not amenable to wall removal using direct implementation of filtering or projection techniques. In this case, we apply CS at each antenna individually to recover the corresponding range profile and estimate the scene response at all frequencies. In applying CS, we use prior knowledge of the wall standoff distance to speed up the convergence of the orthogonal matching pursuit for sparse data reconstruction. Real data are used for validation of the proposed approach.
89 citations
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TL;DR: This work presents a review of the CS-based scene reconstruction techniques that address the unique challenges associated with fast and efficient imaging in urban operations, and focuses on ground-based imaging systems for indoor targets.
Abstract: Through-the-wall radar imaging (TWRI) is emerging as a viable technology for providing high-quality imagery of enclosed structures. TWRI makes use of electromagnetic waves to penetrate through building wall materials. Due to the “see” through ability, TWRI has attracted much attention in the last decade and has found a variety of important civilian and military applications. Signal processing algorithms have been devised to allow proper imaging and image recovery in the presence of high clutter, which is caused by front walls and multipath due to reflections from internal walls. Recently, research efforts have shifted toward effective and reliable imaging under constraints on aperture size, frequency, and acquisition time. In this respect, scene reconstructions are being pursued with reduced data volume and within the emerging compressive sensing (CS) framework. We present a review of the CS-based scene reconstruction techniques that address the unique challenges associated with fast and efficient imaging in urban operations. Specifically, we focus on ground-based imaging systems for indoor targets. We discuss CS-based wall mitigation, multipath exploitation, and change detection for imaging of stationary and moving targets inside enclosed structures.
85 citations
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TL;DR: In this article, a simple through-the-wall radar system for moving target localization is proposed based on trilateration and range estimation from three independent dual-frequency CW radar units.
Abstract: A simple through-the-wall radar system for moving target localization is proposed. This scheme is based on trilateration and range estimation from three independent dual-frequency CW radar units. The dual-frequency technique uses phase comparison of the transmitted and received CW signals to provide an estimate of the range-to-motion. The difference in frequency of the two CW carriers determines the maximum unambiguous range of the target. The range estimates from the three independent CW radar units are then combined using trilateration for target localization. The composition and thickness of the wall, its dielectric constant, and the angle of incidence all affect the characteristics of the signal propagating through the wall. The propagating signal slows down, encounters refraction, and is attenuated as it passes through the wall. If unaccounted for, the non-line-of-sight propagation due to refraction and the slowing down of the waves will introduce a bias in the estimated target location. Our scheme takes into account the presence of the wall and corrects for its refraction and speed of propagation effects. Proof of concept is provided using simulated data. The results show that the proposed dual-frequency CW radar system is able to correctly locate and track moving targets behind walls.
52 citations
References
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TL;DR: An overview of challenging issues for the collaborative processing of wideband acoustic and seismic signals for source localization and beamforming in an energy-constrained distributed sensor network.
Abstract: Distributed sensor networks have been proposed for a wide range of applications. The main purpose of a sensor network is to monitor an area, including detecting, identifying, localizing, and tracking one or more objects of interest. These networks may be used by the military in surveillance, reconnaissance, and combat scenarios or around the perimeter of a manufacturing plant for intrusion detection. In other applications such as hearing aids and multimedia, microphone networks are capable of enhancing audio signals under noisy conditions for improved intelligibility, recognition, and cuing for camera aiming. Previous developments in integrated circuit technology have allowed the construction of low-cost miniature sensor nodes with signal processing and wireless communication capabilities. These technological advances not only open up many possibilities but also introduce challenging issues for the collaborative processing of wideband acoustic and seismic signals for source localization and beamforming in an energy-constrained distributed sensor network. The purpose of this article is to provide an overview of these issues.
528 citations
"A noncoherent radar system approach..." refers background in this paper
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TL;DR: In this paper, a polynomial-type solution for 3D position estimation based on range measurements from three stations is proposed, which facilitates the performance analysis and provides an exact, explicit, and computationally efficient solution.
Abstract: A new exact, explicit, and computationally efficient solution for three-dimensional (3-D) position estimation based on range measurements from three stations is proposed. The simple polynomial-type form of the new algorithm facilitates the performance analysis. Formulae are provided for both the variance and the bias of the position estimates. The systematic error is a joint effect of both the measurement noise and the system nonlinearity and its magnitude cannot be ignored if highly accurate localization is required. Performance evaluation results are presented for various conditions.
327 citations
"A noncoherent radar system approach..." refers methods in this paper
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TL;DR: In this paper, a survey was conducted for the Joint Project Steering Group (JPSG) of the National Institute of Justice (NIJ) and Defense Advanced Project Research Agency (DARPA) to determine the state of the art at the present time in through-the-wall surveillance (TWS) technology and the expected advances within the next 10 years.
Abstract: Recently, a survey was conducted for the Joint Project Steering Group (JPSG) of the National Institute of Justice (NIJ) and Defense Advanced Project Research Agency (DARPA)to determine the state-of-the-art at the present time in through-the-wall surveillance (TWS) technology and the expected advances within the next 10 years. The applicable technologies for TWS include: impulse radar, UHF/microwave radar, millimeter wave radiometry, x-ray transmission and reflectance, and acoustics. Proposed sensors include: monostatic radar, bistatic (or multistatic) radar, radiometers, fixed antenna systems, scanning systems, and focal plane array systems. The ability to penetrate walls leads to a natural conflict between the desire to successfully penetrate walls, which implies lower frequencies and the desire to obtain maximum resolution, which implies higher frequencies. Another conflict involves sophistication of the sensor versus unit cost. These issues and the approaches taken by various developers to find workable solutions are discussed.
146 citations
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DOI•
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01 Dec 1986
TL;DR: In this paper, the basic bistatic properties which depend on the target range and direction relative to the baseline are considered, and appropriate formulas are given and comparisons with monostatic radar are made, pictorially wherever possible.
Abstract: Unless the separation between transmitter and receiver is small compared with ranges of interest, bistatic radars have a number of properties which differ significantly from the monostatic equivalents. Some of these produce operational advantages which provide a motivation for deployment, while others merely bring trouble and expense. The paper considers the basic bistatic properties which depend on the target range and direction relative to the baseline. Appropriate formulas are given and comparisons with monostatic radar are made, pictorially wherever possible. The topics covered are (i) the lower-level cover obtained on a curved earth, (ii) contours of constant `range' and echo power, (iii) the effects of beamwidths on resolution cells and the permissible pulse repetition frequency (PRF), and (iv) the width and direction of the receiving arc.
143 citations
"A noncoherent radar system approach..." refers background in this paper
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18 Feb 1997
TL;DR: In this article, a small, light weight, low power "radar" is developed, based upon the phenomena that optimized radio waves can penetrate non-metallic materials, which can help provide information about what is in a wall, ceiling or floor or on the other side of a door or concrete wall.
Abstract: The Department of Defense (DoD) has funded a dazzling array of 'high tech' solutions for many of the problems facing our military forces. Many of these 'solutions' have been effective for long range mass destruction but have not been applicable for the close-in hand-to-hand combat that we find in the streets. Our goal has been to convert 'high tech' DoD capabilities into cost effective tools to help law enforcement agencies do their jobs better. Surveillance systems presently used by law enforcement officers make extensive use of television, infrared and other line-of- sight surveillance hardware. However, these systems cannot tell what is happening on the other side of a wall, behind bushes, around the corner, in the dark or through a dense fog. A new sensor has been developed, based upon technology developed by the DoD for missile warhead fusing. This small, light weight, low power 'radar' is based upon the phenomena that optimized radio waves can penetrate non-metallic materials. This new surveillance capability can help provide information about what is in a wall, ceiling or floor or on the other side of a door or concrete wall. This paper discusses some applications to show how this radar works and some of the phenomenology which is unique to material penetrating radar systems.
72 citations
"A noncoherent radar system approach..." refers background in this paper
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