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Radar, Sonar and Navigation, IEE Proceedings -

Issue 6 • Date Dec 1999

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Displaying Results 1 - 6 of 6
  • Cell-averaging CFAR detection in compound clutter with spatially correlated texture and speckle

    Page(s): 279 - 284
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (428 KB)  

    The authors study the problem of a CA-CFAR, cell-averaging constant false alarm rate, detection of a Swerling II target model embedded in spatially correlated K-distributed clutter. The clutter model consists of the product of two components called `texture' and `speckle'. Two cases are analysed; in the first case, the speckle samples are correlated and the texture samples are independent while in the second one, both components of the texture and speckle are correlated. Simulations for integer and half-integer values of the shape parameter are conducted to assess the detection performance and the results are presented and discussed View full abstract»

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  • Application of chaos theory to ray tracing in ducts

    Page(s): 298 - 304
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (604 KB)  

    To predict the radar cross section of large ducts and cavities it is common to employ ray tracing methods of one kind or another. Electromagnetic engineers traditionally employ a first-order ray theory based on the Deschamps (1972) formulation. This is not the only formulation and it is shown that the semi-classical tangent-plane methods employed in quantum physics offer some advantages. The special case of straight ducts of arbitrary cross section in considered where the existing theory of billiard dynamics shows that such ray tracing is in general a chaotic process. In a duct or cavity the average rate of increase of ray divergence or change in ray intensity is thus proportional to the Lyapunov exponent. A relationship is provided between the accuracy of the geometry and/or mesh size, the angle of incidence, the duct length and the Lyapunov exponent for a straight duct. This establishes a computational limit on the ability to make numerically deterministic predictions using shooting-and-bouncing or related ray-tracing methods. For a sufficiently long duct of general cross section, away from normal incidence, it is not possible to achieve convergence using these methods View full abstract»

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  • Application of momentary Fourier transform to SAR processing

    Page(s): 285 - 297
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1020 KB)  

    A common technique in signal and image processing is to extract a portion of the signal by windowing, and then perform the DFT on the window contents. The momentary Fourier transform (MFT) applies to the particular case where the window is moved one data sample along the signal between successive transforms. An alternative derivation of the recursive form of the MFT using general matrix transforms is given. How DFTs and IDFTs are used in the SPECAN (spectral analysis) and SIFFT (short IFFT) methods of synthetic aperture radar (SAR) processing is described. The MFT and inverse MFT are applied to those methods and the advantages and disadvantages they have compared to the FFT/IFFT algorithms are shown View full abstract»

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  • Ship target detection for HF groundwave shipborne OTH radar

    Page(s): 305 - 311
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (580 KB)  

    The spreading of the first order Bragg lines that result from movement of the radar platform will obscure targets with Doppler frequencies within the range of this spreading. This is the main difficulty for HF groundwave OTH radar in detecting ship targets in a shipboard environment. In the paper, the properties of the spread spectrum are analysed with the aid of synthetic aperture theory, the possibility of detecting targets in the spread spectrum is shown, and the technique for target detection is presented. The main factors affecting performance of target detection are studied. The experimental results further demonstrate the effectiveness of the technique View full abstract»

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  • Duration of radar false alarms in band-limited Gaussian noise

    Page(s): 273 - 278
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (408 KB)  

    The duration of threshold crossings is investigated for the envelope of band-limited Gaussian noise. The results are applied to the estimation of false alarm times for radar detection and it is shown that the average duration of threshold crossings may be much less than the reciprocal of the noise bandwidth. The average shape of large excursions of the envelope of noise is given by the autocorrelation function, ACF, of the noise. It is shown how the ACF can be combined with the probability density function of the peak values of the noise to give an approximate expression for the average duration of threshold crossings. The accuracy of this expression has been investigated by Monte Carlo simulation and good agreement is achieved when the probability of exceeding a threshold (probability of false alarm) is less than about 10 -2 View full abstract»

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  • Nonlinear frequency modulation chirps for active sonar

    Page(s): 312 - 316
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (432 KB)  

    Range sidelobe suppression in pulse-compression radars and sonars is conventionally performed using amplitude windowing in either the time or frequency domains. Using peak power limited transmitters, this inevitably causes a degradation in the signal-to-noise ratio available at the receiver output owing to shading or mismatch losses. Nonlinear frequency modulation (NLFM) chirps have been suggested as a solution to this problem and have been successfully implemented in a number of radar systems. Using appropriate NLFM functions it is possible to shape the energy spectrum of a chirp, achieving low-range sidelobes, without the need for any amplitude windowing and hence maintaining maximum efficiency. In the field of active sonar, NLFM chirps have been largely ignored because of their poor Doppler tolerance compared with conventional linear period modulation (LPM) chirps. It is shown that a combination of amplitude windowing and NLFM can be used to achieve a compromise between sidelobe suppression, Doppler tolerance and shading loss. Using a novel family of NLFM functions a significant performance advantage over LPM chirps can be attained over a useful range of target velocities. Experimental results support this argument 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.

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