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Radar, Sonar and Navigation, IEE Proceedings -

Issue 6 • Date Dec 1997

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Displaying Results 1 - 11 of 11
  • Comments on “Systematic errors in ground referenced geometric height monitoring”

    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (44 KB)  

    Manolakis and Lefas see (IEE Proc.-F, vol.140, no.2, p.138-44, 1993) mentioned that the errors in range measurements are due to inner mode delay differences, the effects of bottom and top antenna switching and other factors, such as varying range delay and bias correction quantisation factors, along with transponder time delay. This error is treated by the authors as fixed bias. In general, it is not uniform throughout. The end behaviour is influenced by many factors and therefore cannot be adequately modelled by deterministic variables, and hence this error is to be treated as a random time function View full abstract»

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  • New time-domain clutter-lock algorithm

    Page(s): 341 - 347
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    The authors present a new clutter-lock algorithm to estimate the Doppler spectrum centre frequency. The algorithm is based on the fact that the number of zero crossings in the in-phase and quadrature channels is minimum when the azimuth received signal is base-band converted by using the correct Doppler centroid. Although the problem of estimating the Doppler centre frequency is of interest in many fields, the authors investigated the performance of the proposed algorithm when used in the context of SAR data focussing. First, the authors briefly recall the problem of SAR signal processing, then they introduce the proposed algorithm. Its validity is demonstrated by applying it both to simulated and real data. Finally, the algorithm is compared to existing clutter-lock techniques in terms of both estimation accuracy and processing time View full abstract»

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  • Direction finding on spread-spectrum signals using the time-domain filtered cross spectral density

    Page(s): 315 - 320
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (568 KB)  

    In an earlier paper, it was shown that spread-spectrum signals of arbitrary unknown waveform could be detected at received powers well below the receiver noise level, by crosscorrelating the signals from two spatially separated antennas, windowing the crosscorrelation function (CCF) over a narrow range about zero time shift and taking its Fourier transform, thus forming the time-domain filtered cross spectral density (TDFCSD). The authors show that, having detected the signal and established its bandwidth, it is possible to estimate its angle of arrival (AOA) by measuring the phase slope in the TDFCSD across the signal bandwidth. An analysis of the technique is presented showing how the direction finding (DF) accuracy varies with signal and receiver parameters. Computer simulation results show that, with an antenna spacing as low as 1 m, a DF error of less than 1° can be obtained on a signal with a bandwidth of 100 MHz at a received power level lower than -100 dBm, using an integration time of a few milliseconds. A practical system based upon an acousto-optic correlator capable of computing the CCF in real time is described. Preliminary results from the system show DF errors that are in good agreement with theory View full abstract»

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  • Comparison of the ultimate direction-finding capabilities of a number of planar array geometries

    Page(s): 321 - 329
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (744 KB)  

    Although the properties of direction-finding (DF) algorithms have been investigated extensively, the fundamental effects of the array configuration on the performance of DF systems remain unknown. Furthermore, it is often overlooked that there are some theoretical lower limits on the DF performance which are imposed by the array geometry itself. In the paper eight diverse array geometries of elevated feed monopoles, which are used in a number of experimental sites in the UK, are investigated and compared using the ultimate detection, resolution and accuracy thresholds as figures of merit View full abstract»

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  • Statistical modelling of ocean SAR images

    Page(s): 348 - 354
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (516 KB)  

    The paper considers the statistical modelling of fully developed backscattering in the case of SAR images of the ocean surface. According to the random-walk theory, the SAR image grey level is modelled as the product of a speckle noise and a variable which is dependent on the reflectivity of the illuminated surface and the radar-point-spread function. The purpose of the study is the statistical modelling of the latter variable. As nothing is known about these statistics, the authors propose the use of an estimation method based on a system of distributions. The set contains known density-probability functions with very flexible shapes that are supposed to fit its distribution. The associated image intensity distributions are processed and form a new system called KUBW, referring to the special functions used to generate the distributions. The classical K law belongs to the new system of distributions. By using a statistical test on the intensity distribution, the authors assess the relevance of the system of distributions in comparison with the classical model. The paper concludes with a discussion of the merits of the method and its extension to the case of ocean SAR image applications View full abstract»

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  • Erratum

    Page(s): 378 - 379
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (740 KB)  

    First Page of the Article
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  • Radar target discrimination using a hybrid E-pulse fourth-order moments technique

    Page(s): 355 - 360
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (588 KB)  

    A variant of the original extinction pulse (E-pulse) technique for radar target discrimination is proposed. The scheme includes, before convolution with the E-pulse discriminant waveform, a new stage in which the fourth-order moments sequence of the unknown-target impulse-response, r(t), is estimated. To justify this inclusion, it has been shown previously that, by using a particular set of one-dimensional slices on the fourth-order moments space and an appropriately defined `covariance-type' estimator, this moments sequence retains the same damped complex exponential structure as signal r(t), thus only containing the natural resonances of the unknown target. Simulation results clearly show that significant improvements are achieved by using the fourth-order moments sequence of r(t) as the unknown-target signature, instead of the original signal r(t) in the E-pulse discrimination scheme. These results are especially notable when high levels of additive Gaussian noise, white or coloured, are present in r(t) View full abstract»

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  • Array pattern synthesis and robust beamforming for a complex sonar system

    Page(s): 370 - 376
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (852 KB)  

    In modern radar, sonar and wireless communication systems digital beamforming technology based on sensor arrays is widely used to suppress unwanted interfering signals and detect interested target signals. Beam synthesis for arbitrary arrays and beamforming for imperfect arrays are two crucial technical issues associated with digital beamforming. In a complex volumetric underwater acoustic transducer array, due to structural shadowing and scattering, the practical beam pattern significantly deviates from its designed pattern, which would greatly degrade the detection and direction-finding performance of the sonar system. An efficient method is proposed to design beam patterns for arbitrary arrays and is applied to robust beamforming for this sonar system. Sea experimental results show that the proposed robust beamforming method achieves a much lower sidelobe level and a much higher direction-finding accuracy than the conventional beamforming technique View full abstract»

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  • Space-time adaptive processing for airborne radar with various array orientations

    Page(s): 330 - 340
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1044 KB)  

    Space-time adaptive processing (STAP) is a crucial technique for the new generation airborne radar with high air-to-ground performance. The authors study this technique applied to airborne early warning (AEW) radars with various array orientations, which include the sideways looking array radar (SLAR) and non-sideways looking array radar. First, the ground clutter is characterised by showing the angular-Doppler spectra and Doppler-range relation for various array orientations. Secondly, the impact of various array configurations and pulse repetition frequencies (PRFs) on the STAP performance by the use of a multiple Doppler channels joint adaptive processing (M-CAP) approach is analysed. Thirdly, a 3-Doppler-channel processing scheme, in coordination with the various PRF modes, is recommended to solve the STAP problem for practical AEW radars with various array orientations. Finally, some examples are given by simulation to show the performance of the 3-Doppler-channel processing scheme for various cases of interest and to validate the theoretical analysis View full abstract»

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  • Hybrid procedure for CFAR in non-Gaussian clutter

    Page(s): 361 - 369
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (852 KB)  

    The paper deals with false alarm regulation in the presence of non-Gaussian clutter through a hybrid clutter-map/L-filtering technique. The authors propose a new system wherein the adaptive threshold is formed starting with a set of range cells, grouped in a map cell, whose returns are filtered through a nonlinear system, and subsequently processed on a scan-by-scan basis. It is shown that, with suitable choice of the coefficients of the L-filters, the scheme achieves CFAR in all cases where the clutter distribution is of location-scale type or can be forced into this class through suitable transformations. The authors also tackle the problem of system optimisation, showing that the minimum-variance estimators of the adaptive threshold are simply the linear combination of the corresponding optimum estimators of the clutter location and scale parameters. A thorough performance assessment is presented, assuming Weibull and lognormal clutter: it is shown that the new system largely outperforms all the other biparametric systems. Moreover, proper sample censoring allows the prevention of the self-masking effect from slow targets, whether point-like or range-spread, which persist in the same map cell for several scans View full abstract»

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  • Adaptive joint probabilistic data association algorithm for tracking multiple targets in cluttered environment

    Page(s): 309 - 314
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (528 KB)  

    A joint probabilistic data association filter that uses adaptive update times for tracking targets in a cluttered environment is presented and compared with the joint probabilistic data association filter that uses a constant update time. The tracking performance of the algorithm is assessed by Monte Carlo simulations on different target trajectories 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