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Radar, Sonar and Navigation, IEE Proceedings -

Issue 4 • Date Aug 1994

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Displaying Results 1 - 8 of 8
  • Complete processing system that uses fuzzy logic for ship detection in SAR images

    Page(s): 181 - 186
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (436 KB)  

    The automatic interpretation of synthetic aperture radar (SAR) images is one of the most interesting and important application fields of image processing. The authors present a complete digital signal processing chain for the automatic detection of ships in SAR images. Particular attention has been devoted to two problems: the prefiltering problem which aims to reduce the speckle noise in the image, and the robustness problem that is related to the optimisation of the true-target detection/rejection capability. The processing chain has been implemented and tested on a sequential machine and on a parallel architecture of IMS T800 transputers View full abstract»

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  • Improved radar tracking using a multipath model: maximum likelihood compared with eigenvector analysis

    Page(s): 213 - 222
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (656 KB)  

    The performance of the MUSIC algorithm and many other superresolution methods degrades severely with the highly correlated multipath signals encountered in radar low-angle tracking. The paper presents a new eigenvector-based method in which the search vector is replaced by a deterministic specular multipath model. The performance is then compared with that of maximum likelihood using the same model and the well known MUSIC algorithm using spatial smoothing. Simulations and experiments at X-band indicate that the use of a specular model combined with an array radar having frequency agility gives much more accurate tracking than the conventional approaches. The experiments were conducted at Sylt (North Sea), Germany, using corner reflectors mounted on poles inserted in the sea bed; sea conditions varied from sea-state one to five View full abstract»

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  • Switching system for single antenna operation of an S-band FMCW radar

    Page(s): 241 - 248
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (672 KB)  

    Increasing interest is being shown in frequency modulated continuous wave (FMCW) radars due to their advantages of compact size, low peak power requirement, good range resolution and low interference to other systems. A major disadvantage of FMCW systems is the need to use two separate, well shielded antennas for transmission and reception. Several schemes have been devised to enable FMCW radars to operate with a single antenna. The authors describe a ground based S-band ocean surface remote sensing FMCW radar that has been adapted for single antenna operation by alternately switching the single antenna between the transmitter and the receiver. Even though this frequency modulated interrupted continuous wave (FMICW) system is no longer a true continuous wave radar, the essential properties of the FMCW waveform are preserved, provided some conditions on the switching speed and FMCW parameters are met. The purpose of the radar is to deduce ocean wave and current parameters by measuring ocean surface velocities. The radar was tested operationally by comparing ocean surface data from both the single antenna (FMICW) and dual antenna (FMCW) systems recorded under similar conditions View full abstract»

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  • Recursive super-resolution algorithm for low-elevation target angle tracking in multipath

    Page(s): 223 - 229
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (468 KB)  

    Conventional methods of tracking a target using monopulse radar are severely limited in the presence of multipath, particularly at low-elevation angles. A technique using recursive eigendecomposition together with frequency-agile waveforms for tracking low-elevation targets in multipath has been developed. Frequency agility decorrelates the coherence of the direct and specular components on a pulse-to-pulse basis. This frequency agility also provides some robustness to the severe signal cancellation that arises when the direct and specular components are 180° out of phase. The proposed high-resolution, eigenstructure-based algorithm for solving the low-angle tracking problem can be implemented in three steps: (i) updating the covariance matrix, (ii) updating the eigenvalue decomposition of the covariance matrix, and (iii) updating the angle estimates by searching for the peaks of the updated MUSIC spectrum, or solving the zeros derived by the minimum-norm polynomial coefficient. In addition, a phased-array implementation using three orthogonal simultaneous beams placed at half null-beamwidth apart has been developed. The angles can be determined by explicit computation or by a calibration curve in a lookup table such as in monopulse processing for angle estimation using two simultaneous beams View full abstract»

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  • Estimation of texture parameters in K-distributed clutter

    Page(s): 196 - 204
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (584 KB)  

    The authors analyse some of the problems associated with estimating the order parameter of K-distributed high-resolution radar clutter. They identify the cause of these problems to be the nonlinear inversion of various texture measures to the order parameter of the texture. Accordingly, they propose a reciprocal parameter to describe the order. They derive the resultant systematic and random errors in the new texture descriptor, and demonstrate that this removes many of the problems. Simulations now show agreement with the predicted bias and variance, while the bias is significantly smaller than before. It is also confirmed that the normalised log texture measure remains more accurate than others which have been proposed, and approximates the maximum likelihood solution to the estimation of the order parameter over most of the range of interest View full abstract»

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  • Performance of some generalised modified order statistics CFAR detectors with automatic censoring technique in multiple target situations

    Page(s): 205 - 212
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (436 KB)  

    The author presents three generalised modified OS CFAR detectors and an automatic censoring technique. These three new OS CFARs are: a generalised ordered statistic cell averaging (GOSCA) CFAR, a generalised order statistic greatest of (GOSGO) CFAR and a generalised ordered statistic smallest of (GOSSO) CFAR. For these three new OS CFAR detectors the author obtains analytic expressions of the false alarm rate, the detection probabilities and the measure ADT under the Swerling 2 assumption. He analyses their detection performance in homogeneous background and in the presence of strong interfering targets, and compares them to several previously proposed CFARs. This analysis shows that the GOSCA CFAR detector has the best detection performance among the OS and the several modified OS CFAR detectors. Since a new automatic censoring technique is used in the CFAR detectors, this makes the GOSGO and GOSSO CFARs more robust than the OSGO and OSSO CFARs. When the number of strong interfering targets attains the greatest interfering targets allowed, the performance of the OS CFAR is worst among the GOSCA, GOSGO, GOSSO and OS CFAR detectors View full abstract»

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  • Comparison between linear FM and phase-coded CW radars

    Page(s): 230 - 240
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    The classical linear FM CW radar signal is compared with P3 and P4 phase-coded CW signals. The comparison covers the theoretical delay-Doppler response, the spectrum and the performances in digital receiver processors. The receivers produce a matrix of delay and Doppler cells. Three receiver approaches are considered: (a) Doppler compensation followed by a multicorrelation processor. This is a general and efficient implementation of many matched filters, which applies to any phase-coded signal. (b) A modification of (a), applicable to P3, P4 signals, in which the multicorrelators are efficiently replaced by FFTs, without altering the performances. (c) A single correlator followed by two levels of spectral analysis, for range and for Doppler. In the two matched filter implementations, (a) and (b), the P signals exhibit lower range sidelobes, due to their inherent property of perfect periodic autocorrelation. The LFM signal requires additional weighting (hence additional SNR loss) and even then does not approach the low range sidelobes of P signals. In the single correlator receiver, the two signals exhibit almost identical performances, which are similar to the performances of LFM in the matched receiver View full abstract»

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  • Analysis of the adaptive space time processing technique for airborne radar

    Page(s): 187 - 195
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (580 KB)  

    The paper analyses the adaptive space/time processing technique for clutter rejection, and shows how it relates to the more traditional DPCA (displaced phase centre antenna) methods. It is demonstrated that, in SLAR (sideways looking airborne radar) applications, adaptive space/time processing can result in weight solutions equivalent to those required to perform DPCA. Sufficient conditions for the optimal space/time solution to be close to a DPCA type solution are given. Factors which influence the form of the adaptive space/time solution are considered and bounds on the number of eigenvalues of the space/time clutter covariance matrix are derived. Finally, simulation results, which lend support to the conclusions reached through theoretical analysis, are presented View full abstract»

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Aims & Scope

IEE Proceedings Radar, Sonar and Navigation covers the theory and practice of systems involving the processing of signals for radar, radio location, radio navigation and surveillance purposes.

Full Aims & Scope