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检索条件"任意字段=Radar Sensor Technology VIII and Passive Millimeter-Wave Imaging Technology VII"

共 54 条记录，以下是41-50 订阅

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High resolution passive millimetre-wave imaging technologies for reconnaissance and surveillance

High resolution passive millimetre-wave imaging technologies...

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Conference on passive millimeter-wave imaging technology VI and radar sensor technology vii

作者： Peichl, M Süss, H Dill, S DLR German Aerosp Ctr Microwaves & Radar Inst D-82234 Wessling Germany

ISBN: (纸本)0819449369

This paper addresses the use of high resolution aperture synthesis radiometry for the purpose of reconnaissance and surveillance on an Unmanned Aerial Vehicle (UAV) platform. A short introduction to the military background for the applicability of this technique is given. The phenomenology of microwave radiometry is shortly introduced and range considerations are outlined. The principles of aperture synthesis are presented and a first design idea based on previous investigations for a low-expense system is given. Based on that the imaging performance of the system is investigated using a typical brightness temperature scene from earlier linescanner measurements at 90GHz. The array thinning, the finite sensitivity, and the impact of non-ideal flight maneuvers are discussed. It is shown, that the low-expense system is able to produce satisfying results for target detection.

关键词： aperture synthesis radiometry UAV reconnaissance surveillance high resolution sparse array sensitivity

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Adaptive system for detecting stationary targets with real-aperture radar

Adaptive system for detecting stationary targets with real-a...

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Conference on passive millimeter-wave imaging technology VI and radar sensor technology vii

作者： Khatri, H Koenig, F Innocenti, R Ranney, K USA Res Lab Adelphi MD 20783 USA

ISBN: (纸本)0819449369

Trained algorithms are required for detecting stationary targets with practical real-beam radars. The parameters of these algorithms are unique to each site or clutter class. A problem arises when an algorithm trained on one clutter class is applied, perhaps inadvertently, to another class. In this case, the performance of the system can degrade to an unacceptable level. We have developed a system that adapts, online, the parameters of the algorithm to the encountered clutter type. This system consists of two neural networks - one for adapting the coefficients of the algorithm and the other for adapting the threshold level.

关键词： detection stationary target neural network genetic algorithm

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Further designs of opto-mechanical scanners for use in passive mm-wave imaging

Further designs of opto-mechanical scanners for use in passi...

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Conference on passive millimeter-wave imaging technology VI and radar sensor technology vii

作者： Lettington, AH Dunn, D Attia, M Blankson, IM Univ Reading Reading RG6 6AF Berks England

ISBN: (纸本)0819449369

Mm-wave imaging has high potential for all weather performance but requires large apertures to achieve acceptable spatial resolution. These large apertures need to collect radiation from a range of angles in the field of view and form a two dimensional image. The ideal method for achieving such an image would be to have an aperture completely filled with receivers and to electronically beam-form. Unfortunately this technology is not sufficiently developed at present to make this a practical proposition. Receivers are far too expensive to form a completely filled aperture and the technology of beam forming is still under development. The alternative and most cost effective solution at present is to have a comparatively small number of receivers and scan them across the scene using an opto-mechnaical scanner. In scanned thermal imaging systems it is usual to employ high speed rotating polygons to perform the line scan and a flapping mirror for the framing motion. The pupil size is typically 10mm in thermal imaging and the polygons are 40mm in diameter. If such an arrangement were used at mm-wavelengths where the pupil size is of the order of 1m, the rotating polygon would be 4m in diameter. The paper describes new compact opto-mechanical systems based on rotary discs, prisms and using frequency and polarization selective surfaces.

关键词： passive millimeter wave imaging PMMW scanning

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A new approach to deinterleaving for radar intercept receivers

A new approach to deinterleaving for radar intercept receive...

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Conference on passive millimeter-wave imaging technology VI and radar sensor technology vii

作者： Frankpitt, B Baras, J Tse, A AIMS Inc Rockville MD 20852 USA

ISBN: (纸本)0819449369

We present a new approach to the design of deinterleavers for radar intercept receivers. We design the deinterleaver to target frequency and pulse repetition frequency (PRF) agile pulse Doppler emitters, a class of radar sources that is difficult to deinterleave with traditional approaches. Targeting this specific class of emitters allows us to take advantage of the coherent processing signal structure that is common to emitters in the class. The deinterleaver extracts constant pulse repetition interval (PRI) pulse packets from the receiver signal, and then clusters the pulse packets on the basis of coherency. Pulse packets that come from the same radar source form coherent signal structures, pulse packets from different sources do not. The paper describes the filtering algorithms that extract the pulse packets, presents an analysis of signal coherency that provides a priori estimate of the effectiveness of the design, and describes the clustering algorithms that separate the pulse packets into deinterleaved signal streams.

关键词： radar receivers

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millimeter-wave radiometric measurements of a treeline and building for aircraft obstacle avoidance

Millimeter-wave radiometric measurements of a treeline and b...

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Conference on passive millimeter-wave imaging technology VI and radar sensor technology vii

作者： Wikner, DA USA Res Lab Adelphi MD 20783 USA

ISBN: (纸本)0819449369

passive millimeter-wave (MMW) imagers have the potential to be used on low-flying aircraft for terrain-following / terrain-a voidance during low-visibility conditions. This potential exists because of the inherent nature of MMW radiation that allows it to penetrate many visible and IR obscurants such as fog, clouds, and smoke. The phenomenology associated with this application, however, has not been fully explored. Specifically, the radiometric signatures of the various obstacles that might be encountered during a low-altitude flight need to be thoroughly understood. The work described in this paper explores the 93-GHz passive signature of a deciduous treeline and a concrete/glass building. The data were taken from the roof of a 4-story building to simulate the view of a low-flying aircraft. The data were collected over many months with an ARL-built Stokes-vector radiometer. This radiometer is a single-beam system that raster scans over a scene to collect a calibrated 93-GHz image. The data show the effects of weather and tree lifecycle on the 93-GHz brightness temperature contrast between the horizon sky and the obstacles. For the case of trees, it is shown that the horizon sky brightness temperature is greater than that of the trees when the leaves are on because of the reflective properties of the leaves. This made the trees quite detectable to our system during the late spring, summer, and early fall. Concrete buildings are inherently low-contrast obstacles because their vertical nature reflects the horizon behind the sensor and can easily mimic the forward horizon sky. Solar loading can have a large effect on building signatures.

关键词： passive millimeter-wave imaging buildings treeline collision avoidance

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Wideband adaptive beamforming to control time sidelobes and null depth

Wideband adaptive beamforming to control time sidelobes and ...

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Conference on passive millimeter-wave imaging technology VI and radar sensor technology vii

作者： Rabideau, DJ Parker, P MIT Lincoln Lab Lexington MA 02420 USA

ISBN: (纸本)0819449369

High resolution radars use wide bandwidth waveforms to create images of unknown objects. In military systems, such radar images can be used for target identification and discrimination functions as long as the time sidelobes are kept low. However, the need for low sidelobes imposes constraints on the design of the radar in general, and the signal processing in particular. Furthermore, since military radars must operate in the presence of strong interference, wideband Adaptive Beam Forming techniques (ABF), such as Space-Time Adaptive Processing (STAP), are needed. This paper describes signal processing techniques for wideband digital radars that utilize stretch processing at each receiver. It analyzes the impact of stretch ABF techniques on time sidelobes, showing how sidelobe levels depend on the ABF architecture. It describes the impact of channel errors on time sidelobes and null depth, and proposes a digital filtering architecture for channel equalization, digital beamforming, and STAP.

关键词： adaptive beamforming space-time adaptive processing range sidelobes equalization wideband radar

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Active millimeter-wave imaging for concealed weapons detection

Active millimeter-wave imaging for concealed weapons detecti...

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Conference on passive millimeter-wave imaging technology VI and radar sensor technology vii

作者： Grossman, EN Miller, AJ Natl Inst Stand & Technol Div Electromagnet Technol Boulder CO 80303 USA

ISBN: (纸本)0819449369

Actively illuminated mm-wave imaging systems for concealed weapons detection offer the possibility of much higher sensitivity than with passive systems. We discuss several issues specific to mm-wave imaging systems that are actively illuminated and describe our implementation of such a system. We show that the illumination geometry is critical to the appearance and detectability of targets, and present measurements of the bi-directional reflectance distribution of a small handgun, as a prototypical target. We demonstrate suppression of standing waves using frequency modulated (FMCW) illumination and directly compare images taken with CW, FMCW, and pulsed illumination. Our implementation of an active imaging system is based on a 120-element focal-plane array (FPA) of uncooled antenna-coupled microbolometers. We describe the fabrication process and yield for these FPA's, as well as tests that show the performance of individual pixels on the 120-element array to be equivalent to that of isolated devices. These results demonstrate that wiring for readout of an antenna-coupled FPA can be made "transparent" to the antennas. Therefore, a mm-wave FPA that is read out through wiring to the perimeter of the array constitutes a simple and feasible architecture, in contrast to the infrared, where space limitations require vertical (3D) integration of readout and FPA. The electrical readout system for the FPA is also described. Finally, we present a result obtained with the full FPA system, showing that 3-way illumination is much more effective for detection of a complex target than a single directional illuminator.

关键词： bolometer array millimeter-wave concealed weapons imaging

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radar-target signatures from mmw-measurement platform

Radar-target signatures from mmw-measurement platform

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Conference on passive millimeter-wave imaging technology VI and radar sensor technology vii

作者： Inaebnit, C John, MA Aulenbacher, U Def Procurement Agcy CH-3003 Bern Switzerland

ISBN: (纸本)0819449369

Automatic target detection (ATR) depends on the surrounding clutter as well as on the target signatures. Swiss DoD has established a measurement-platform in the W-Band frequency frame to generate the necessary data. The wavelength of the W-Band is much smaller than the target dimension and the footprint of the antenna does not illuminate the entire target. This has the result, that the actual echo-signal correlates strongly to the view angle. The signature of a target is so complex for any kind of evaluation, that it is necessary to create a statistical model with virtual scatters. As an example this model can be integrated in simulations of smart ammunition effectiveness. With data of a statistical model it is possible: - to evaluate the object according its RCS. - to create the necessary camouflage-precaution against radar-seekers and check there efficiency. - to calculate detection probabilities of a target in different clutter conditions. - to identify strong reflectors and thereby reduce the RCS value of the target.

关键词： radar RCS target signatures smart ammunition simulations modeling procedures

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A study of the effect of buried biomass on ground-penetrating radar performance

A study of the effect of buried biomass on ground-penetratin...

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Conference on passive millimeter-wave imaging technology VI and radar sensor technology vii

作者： Niltawach, N Chen, CC Johnson, JT Baertlein, BA Ohio State Univ Electrosci Lab Columbus OH 43212 USA

ISBN: (纸本)0819449369

It is widely acknowledged that tree roots and other forms of buried biomass have an adverse effect on the performance of ground-penetrating radars (GPRs). In this work we present experimental and theoretical work that quantifies that effect. Test sites containing extensive root infiltration at Eglin Air Force Base, FL were probed with a GPR. After completing the measurements, the sites were excavated, and the root structure and soil were thoroughly characterized. Supplemental GPR measurements of simple cylindrical objects in a laboratory setting were performed to investigate the basic scattering behavior of buried roots. A numerical simulator based on the Discrete Dipole Approximation (DDA), an integral-equation-based method, was developed, validated and subsequently used to compute scattering from root structures modeled by an ensemble of buried cylinders. A comparison of the measurements and numerical calculations is presented that quantifies the potential for false alarms and increased clutter due to buried roots.

关键词： biomass roots ground penetrating radar UXO discrete dipole approximation

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Use of constraints in super-resolution of passive millimeter-wave images

Use of constraints in super-resolution of passive millimeter...

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Conference on passive millimeter-wave imaging technology VI and radar sensor technology vii

作者： Lettington, AH Dunn, D Rollason, MP Alexander, NE Yallop, MR Univ Reading JJ Thomson Phys Lab Reading RG6 6AF Berks England

ISBN: (纸本)0819449369

This paper discusses the use of constraints when super-resolving passive millimeter wave (PMMW) images. A PMMW imager has good all-weather imaging capability but requires a large collection aperture to obtain adequate spatial resolution due to the diffraction limit and the long wavelengths involved. A typical aperture size for a system operating at 94GHz would be I m in diameter. This size may be reduced if image restoration techniques are employed. A factor of two in recognition range may be achieved using a linear technique such as a Wiener filter;while a factor of four is available using non-linear techniques. These non-linear restoration methods generate the missing high frequency information above the pass band in band limited images. For this bandwidth extension to generate genuine high frequencies, it is necessary to restore the image subject to constraints. These constraints should be applied directly to the scene content rather than to any noise that might also be present. The merits of the available super-resolution techniques are discussed with particular reference to the Lorentzian method. Attempts are made to explain why the distribution of gradients within an image is Lorentzian by assuming that an image has randomly distributed gradients of random size. Any increase in sharpness of an image frequently results in an increase in the noise present. The effect of noise and image sharpness on the ability of a human observer to recognise an object in the scene is discussed with reference to a recent model of human perception.

关键词： super-resolution PMMW image restoration inverse problems

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