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

共 57 条记录，以下是21-30 订阅

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Atmospheric loss considerations for synthetic aperture radar design and operation

Atmospheric loss considerations for synthetic aperture radar...

引用

Conference on radar sensor technology viiI and passive Millimeter-wave imaging technology vii

作者： Doerry, AW Sandia Natl Labs Livermore CA 94550 USA

ISBN: (纸本)0819453331

A significant loss factor for Synthetic Aperture radar (SAR) is the atmosphere, particularly under conditions of adverse weather. Dominating these losses are 1) atmospheric clear-air attenuation due to a) oxygen absorption, and b) water vapor absorption., 2) cloud liquid water absorption.. and 3) attenuation due to rain. These losses are very nonlinear with respect to radar operating frequency, and their relative significance obviously depends on the nature of the weather being modeled. Attenuation is also very operating geometry dependent.. and typically increases with range and shallower depression angles. The net effect is that while airborne radar operation at short ranges often favors higher frequencies owing to higher antenna gain for a given real aperture antenna, radar operation at longer ranges often favors lower frequencies in spite of this. In fact.. at any particular range.. an optimal SAR operating frequency that maximizes SNR exists for a given weather condition.. transmitter power, and antenna aperture area. This paper discusses loss rates due to various loss contributors, and then quantifies expected atmospheric loss rates and their frequency dependence for typical adverse weather specifications for SAR systems. Furthermore, this paper describes airborne SAR operating geometries for which various radar frequency bands are optimal.

关键词： SAP radar. atmosphere weather performance

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Improving angular resolution with Scan-MUSIC algorithm for real complex targets using 35-GHz millimeter wave radar

Improving angular resolution with Scan-MUSIC algorithm for r...

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Conference on radar sensor technology viiI and passive Millimeter-wave imaging technology vii

作者： Ly, C USA Res Lab Adelphi MD 20783 USA

ISBN: (纸本)0819453331

Scan-MUSIC algorithm, developed by the U.S. Army Research Laboratory (ARL), improves angular resolution for target detection with the use of a single rotatable radar scanning the angular region of interest. This algorithm has been adapted and extended from the MUSIC algorithm that has been used for a linear sensor array. Previously, it was shown that the SMUSIC algorithm and a Millimeter wave radar can be used to resolve two closely spaced point targets that exhibited constructive interference, but not for the targets that exhibited destructive interference. Therefore, there were some limitations of the algorithm for the point targets. In this paper, the SMUSIC algorithm is applied to a problem of resolving real complex scatterer-type targets, which is more useful and of greater practical interest, particular for the future Army radar system. The paper presents results of the angular resolution of the targets, an M60 tank and an M113 Armored Personnel Carrier (APC), that are within the mainlobe of a K(a)-bandradar antenna. In particular, we applied the algorithm to resolve centroids of the targets that were placed within the beamwidth of the antenna. The collected coherent data using the stepped-frequency radar were compute magnitudely for the SMUSIC calculation. Even though there were significantly different signal returns for different orientations and offsets of the two targets, we resolved those two target centroids when they were as close as about 1/3 of the antenna beamwidth.

关键词： Scan-MUSIC (SMUSIC) angular resolution cross-range resolution closely spaced point targets antenna pattern step-scanned antenna spatial smoothing subvector average real scatterer-type targets phase correction

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passive interferometric millimeter-wave imaging: achieving big results with a constellation of small satellites

Passive interferometric millimeter-wave imaging: achieving b...

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Conference on radar sensor technology viiI and passive Millimeter-wave imaging technology vii

作者： Shao, XM Junor, W Zenick, R Rogers, A Dighe, K Los Alamos Natl Lab Space & Atmospher Sci Grp Los Alamos NM 87545 USA

ISBN: (纸本)0819453331

Los Alamos National Laboratory (LANL) and AeroAstro have recently investigated the feasibility of space-based passive interferometric millimeter wave imaging (PIMI). The goal of this study is to explore a new capability that can offer day/night, all-weather, passive imaging with a 1-meter resolution, by means of millimetric interferometry via a small constellation of microsatellites. According to our preliminary study, a system with four LEO satellites operating at multiple frequency channels within 95-150 GHz is capable of providing an imagery of 1-m spatial resolution. The corresponding temperature sensitivity is estimated to be similar to20degreesK, enough to distinguish most artifacts from a variety of backgrounds. To achieve the stated resolution and sensitivity with only four satellites, we make use of ten frequency channels to synthesize ten effective baselines between any pair of satellites. In addition, the satellites will "stare" at a common target area off the track direction for about 2 minutes while they pass over the area. This type of observation will introduce much improved spatial frequency coverage due to the relative rotation of the baseline vectors. It also improves the imagery SNR with a longer viewing time, as compared to a downward looking system. To the target, the side-looking observation also has the advantage of near constant incident (zenith) angle. The satellites are required to perform a formation flight but a rigid formation is not necessary. Simultaneous interferometric measurement of GPS signals, together with inter-satellites ranging will allow us to monitor the baseline length and direction to an adequate accuracy. A tradeoff study has also been conducted between the system performance and the technology availability, i.e., the current state-of-the-art technologies for space-borne antenna, millimeter-wave receiver, high-speed digitizer, inter-satellites data communication, and so forth.

关键词： interferometric imaging mmw small satellite

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Analysis of passive millimeter-wave imagery texture for enhanced aircraft obstacle avoidance

Analysis of passive millimeter-wave imagery texture for enha...

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Conference on radar sensor technology viiI and passive Millimeter-wave imaging technology vii

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

ISBN: (纸本)0819453331

It has been demonstrated that passive MMW imagers can be used to detect obstacles through the fog, such as treelines and hillsides, which might be encountered in the path of a low-flying aircraft. However, the brightness temperature contrast between the horizon sky and the obstacle can often be quite small in foggy conditions, on the order of 5 K or less. Reliable detection of this contrast without image processing requires a passive MMW imager with a DeltaT(min) of about 0.2 K, which is quite challenging for existing 30-Hz imagers. While improvements in passive MMW imagers continue, it is useful to look at image analysis techniques that have the potential to improve obstacle detection by increasing the amount of information extracted from each image frame. In this paper we look at the ways that texture can be used to extract more information from the imagery. By merging textural information with the brightness temperature contrast information, there is the potential to enhance the detection of objects within the scene. The data used for the analysis presented here is 93-GHz, passive imagery of a deciduous treeline scene and a concrete building scene. 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. Texture measurement results for image segment samples, including autocorrelation and spatial edgeness, are presented in this work. Also presented are the effects of applying a modified Sobel edge detection technique to imagery with the least detectable obstacles.

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

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A portfolio of fine resolution SAR images - continued

A portfolio of fine resolution SAR images - continued

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Conference on radar sensor technology viiI and passive Millimeter-wave imaging technology vii

作者： Doerry, AW Gutierrez, VD Wells, L Sandia Natl Labs Livermore CA 94550 USA

ISBN: (纸本)0819453331

Sandia National Laboratories designs and builds Synthetic Aperture radar (SAR) systems capable of forming high-quality exceptionally fine resolution real-time images. Resolutions as fine as 4 inches (10 cm) in both slant range and azimuth are routinely formed in real time on board Sandia's DeHavilland DHC-6 Twin Otter aircraft using a Ku-band SAR. Resolutions as fine as 6 inches (15 cm) in both slant range and azimuth are routinely formed using an X-band SAR. Careful system design allows high image quality as measured by nearly ideal Impulse Response (IPR) shapes, with typical Multiplicative Noise Ratios (MNR) of better than 20 dB, and a noise equivalent reflectivity usually better than -30 dB. Collection geometries routinely include squint angles 45 degrees both fore and aft of broadside, on either side of the aircraft. This paper offers a collection of high quality images representative of the output of Sandia's testbed radar. High-quality fine-resolution images of a variety of target scenes will be displayed.. with annotation describing relevant image parameters. This paper is the second of a set of two portfolios.

关键词： SAR radar image

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Whole body 35GHz security scanner

Whole body 35GHz security scanner

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Conference on radar sensor technology viiI and passive Millimeter-wave imaging technology vii

作者： Appleby, R Anderton, RN Price, S Sinclair, GN Coward, PR QinetiQ Malvern WR14 3PS Worcs England

ISBN: (纸本)0819453331

A 35GHz imager designed for Security Scanning has been previously demonstrated. That imager was based on a folded conical scan technology and was constructed from low cost materials such as expanded polystyrene and printed circuit board. In conjunction with an illumination chamber it was used to collect indoor imagery of people with weapons and contraband hidden under their clothing. That imager had a spot size of 20mm and covered a field of view of 20 x 10 degrees that partially covered the body of an adult from knees to shoulders. A new variant of this imager has been designed and constructed. It has a field of view of 36 x 18 degrees and is capable of covering the whole body of an adult. This was achieved by increasing the number of direct detection receivers from the 32 used in the previous design to 58, and by implementing an improved optical design. The optics consist of a front grid, a polarisation device which converts linear to circular polarisation and a rotating scanner. This new design uses high-density expanded polystyrene as a correcting element on the back of the front grid. This gives an added degree of freedom that allows the optical design to be diffraction limited over a very wide field of view. Obscuration by the receivers and associated components is minimised by integrating the post detection electronics at the receiver array.

关键词： concealed weapon detection millimetre-wave imaging illumination techniques indoor

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Using radar to help mitigate truck overturn incidents on US interstate highways

Using radar to help mitigate truck overturn incidents on US ...

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Conference on radar sensor technology viiI and passive Millimeter-wave imaging technology vii

作者： Greneker, EF Rausch, EO Georgia Tech Res Inst Radar Syst Div Sensors & Electromagnet Applicat Lab Smyrna GA 30080 USA

ISBN: (纸本)0819453331

The operations of tractor-trailers, mixed with other vehicles on US interstates, has resulted in a number of major tractor-trailer overturn events which often cause traffic to stop for hours along a major traffic corridor because the wreckage physically blocks the corridor. In some cases, the blockage remains for a day or more if toxic substances are being carried by the tractor-trailer. Mixed vehicle use of the interstates coupled with the fact that some tractor-trailers with high center of gravity loads are driven too fast ensure that the overturn events experienced to date will continue. In a previous SPIE paper, the Georgia Tech Research Institute (GTRI) researchers demonstrated that an X-band radar (10.5 GHz) could detect the oscillation frequency of tractor-trailer trucks within 1,000 feet of the radar. This radar was used to control a vibration damper on a bridge to provide longer bridge life. Previous studies conducted by GTRI show that tractor-trailer trucks reflect several orders of magnitude more energy than passenger vehicles, vans and other smaller trucks. In many cases, the large tractor-trailer truck radar signature alone could be used to identify the trucks from the other traffic. However, since non-ranging homodyne radar was being used, it was not known if smaller radar cross section targets that were closer to the radar than the tractor-trailer trucks would have a larger radar signature. This paper examines the issues associated with identifying tractor-trailer truck radar signatures from the radar signatures of other vehicles within the antenna beam of a non-ranging homodyne radar.

关键词： radar Homodyne detection Doppler effect Signal processing radar signal processing X band Antennas Bridges Warning signs

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Image quality specification and maintenance for airborne SAR

Image quality specification and maintenance for airborne SAR

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Conference on radar sensor technology viiI and passive Millimeter-wave imaging technology vii

作者： Clinard, M Consultant (United States)

ISBN: (纸本)0819453331

Specification, verification, and maintenance of image quality over the lifecycle of an operational airborne SAR begin with the specification for the system itself Verification of image quality-oriented specification compliance can be enhanced by including a specification requirement that a vendor provide appropriate imagery at the various phases of the system life cycle. The nature and content of the imagery appropriate for each stage of the process depends on the nature of the test, the economics of collection, and the availability of techniques to extract the desired information from the data. At the earliest lifecycle stages, Concept and technology Development (CTD) and System Development and Demonstration (SDD), the test set could include simulated imagery to demonstrate the mathematical and engineering concepts being implemented thus allowing demonstration of compliance, in part, through simulation. For Initial Operational Test and Evaluation (IOT&E), imagery collected from precisely instrumented test ranges and targets of opportunity consisting of a priori or a posteriori ground-truthed cultural and natural features are of value to the analysis of product quality compliance. Regular monitoring of image quality is possible using operational imagery and automated metrics;more precise measurements can be performed with imagery of instrumented scenes, when available. A survey of image quality measurement techniques is presented along with a discussion of the challenges of managing an airborne SAR program with the scarce resources of time, money, and ground-truthed data. Recommendations are provided that should allow an improvement in the product quality specification and maintenance process with a minimal increase in resource demands on the customer, the vendor, the operational personnel, and the asset itself.

关键词： synthetic aperture radar image quality assurance

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Resolution issues in the analysis of radar signals via fourier approaches

Resolution issues in the analysis of radar signals via fouri...

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Conference on radar sensor technology viiI and passive Millimeter-wave imaging technology vii

作者： Flores, BC Ochoa, HA Thomas, G Univ Texas El Paso TX 79968 USA

ISBN: (纸本)0819453331

Classical work in the field of high-resolution radar often assumes that an echo signal is made of a number of components that can be decomposed via Fourier analysis. Adjacent components are said to be resolved in the frequency domain if the intensity between them drops at least 3 decibels. This working definition is an extension of Lord Rayleigh's criterion for optical resolution. The problem with this approach is that whereas Rayleigh's criterion assumes signal incoherence, thus allowing, for the addition of power components, a high-resolution radar signal is often the coherent sum of sinusoids, which implies voltage addition. The purpose of this paper is to discuss the consequences of using Rayleigh's criterion in the analysis of radar signals. Specifically, computer simulations using a complex signal are analyzed via the periodogram as the relative phase between the two components of the signal is allowed to change. The net effect introduced by this phase variation is to reduce or increase the spacing and intensity between two adjacent spectral peaks. These changes are due to constructive or destructive interference of spectral cross terms that cannot be ignored when attempting to resolve frequency components from one another. For instance, the simulations show that when using the averaged periodogram, the intensity in-between two adjacent components is above the -3 decibel threshold for a phase range of 1.2pi radians, although the standard resolution criterion of c/2beta is satisfied. Similar results are obtained when using a number of windows that are known to control sidelobe levels. Thus, the use of Rayleigh's criterion to define the resolution of a high-resolution radar system is technically inconsistent and undermines our ability to perform quantitative comparisons of target profiles, Doppler profiles and range-Doppler images. In this light, the authors promote the adoption of alternative criteria for judging resolution gains based on the norm of the signal

关键词： resolution Fourier analysis Rayleigh's criterion

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Low cost Ka band SAR/ISAR for UAV applications

Low cost Ka band SAR/ISAR for UAV applications

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radar sensor technology viiI and passive Millimeter-wave imaging technology vii

作者： Kim, Seong Pergande, Al Hughen, James Lockheed Martin Missiles/Fire Contr. 5600 Sand Lake Road Orlando FL 32819

Growing interest in low cost unattended observations has lead Lockheed Martin Missiles and Fire Control to examine and demonstrate feasibility of a small inexpensive SAR/ISAR system at Ka band. By trading off state of the art performance for cost and volume, system performance for UAV applications is still adequate to provide important tactical information to battle field commanders in real time while reducing the exposure of war fighters to hostile fire. As RF and millimeterwave component become cheaper and more robust, system costs are expected to fall further. To demonstrate this concept, we have built a portable system with 500 Mhz instantaneous bandwidth, and have used to it gather SAR and ISAR data along with conventional HRR and LFM target data at Ka Band. Here we present sample data collected with our system along with supporting system performance supporting the use of such inexpensive systems in near term applications.

关键词： Synthetic aperture radar

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