Online ISSN
1751-8792
Print ISSN
1751-8784
IET Radar, Sonar & Navigation
Volume 4, Issue 2, April 2010
Volumes & issues:
Volume 4, Issue 2
April 2010
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- Author(s): S. Watts and K. Ward
- Source: IET Radar, Sonar & Navigation, Volume 4, Issue 2, p. 143 –145
- DOI: 10.1049/iet-rsn.2009.9011
- Type: Article
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- Author(s): K.D. Ward and S. Watts
- Source: IET Radar, Sonar & Navigation, Volume 4, Issue 2, p. 146 –157
- DOI: 10.1049/iet-rsn.2009.0132
- Type: Article
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Radar backscatter from the sea surface has a significant effect on radar systems operating in a maritime environment. This study considers the application of modelling sea clutter to the design and development of such systems, and addresses the sensitivity of the predicted performance to the choice of model. The typical phases of the life-cycle of a radar system are described, along with how models are used to support the radar development. Different types of model are reviewed and some examples are given of the comparison of their effect on predicted performance. The conclusion is that the differences are important and continue to warrant further investigation. - Author(s): L.P. Roy and R.V.R. Kumar
- Source: IET Radar, Sonar & Navigation, Volume 4, Issue 2, p. 158 –167
- DOI: 10.1049/iet-rsn.2009.0108
- Type: Article
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The correct formulation of the likelihood ratio test (LRT)-based detection schemes for a target in the presence of clutter needs a faithful and mathematically tractable clutter model. The state-of-art detection methods usually assume that the land and sea clutter in whose presence a target signal to be detected as K-distributed form of non-Gaussian clutter and uses an LRT detector obtained for the same. However, the macroscopic phenomena of clutter generation in a search radar and also the detailed studies on the measured clutter data show a significant texture fluctuation caused by the continuous antenna scanning motion. Incorporation of the scanning effect in the clutter model introduces challenges in modelling the varying texture and formulating a suitable detection scheme. Here the authors propose a clutter model for such scanning radar applications taking the effect of scanning on the clutter correlation into consideration. A method of fitting the proposed model to measured data and a method of simulating the clutter as per the proposed model are also presented. The proposed model is found to be attractive for an LRT detector design. Further in this study, the proposed clutter model is also validated through a real experimental data which show an excellent match between the simulated and measured data of both sea and land clutters. The close agreement between the model and the measurement clearly illustrates the validity and applicability of the model. - Author(s): G. Davidson
- Source: IET Radar, Sonar & Navigation, Volume 4, Issue 2, p. 168 –177
- DOI: 10.1049/iet-rsn.2009.0075
- Type: Article
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This study provides a brief overview of methods used to simulate sea clutter. It then offers a simple and flexible way of generating non-stationary coherent sea clutter that matches higher order statistics of real clutter in the time domain, as well as the shape and intensity distribution within the Doppler domain. Results confirm that the simulated signal intensity can also be well matched by the K-distribution. - Author(s): G.M. Herbert
- Source: IET Radar, Sonar & Navigation, Volume 4, Issue 2, p. 178 –186
- DOI: 10.1049/iet-rsn.2009.0064
- Type: Article
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The presence of clutter can be highly detrimental to detection of targets in airborne radar systems. Space–time adaptive processing (STAP) attempts to alleviate the problem by exploiting angle–Doppler inter-relationships to suppress clutter. The requirements for modelling of clutter data that are suitable for the application of STAP are considered in this study. Examples of clutter generated using the ELMBAARC program in bistatic and monostatic applications are provided. Modelling of internal clutter motion is considered, together with its effect on the clutter domain in angle–Doppler space. Modelling of non-homogeneous clutter is also considered. - Author(s): P. Fayard and T.R. Field
- Source: IET Radar, Sonar & Navigation, Volume 4, Issue 2, p. 187 –194
- DOI: 10.1049/iet-rsn.2009.0122
- Type: Article
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In the context of a stochastic framework based on Jakeman's random walk model, Field and Tough demonstrated how the radar cross-section could be inferred from the intensity-weighted fluctuations of the phase (coherent data). With regard to the compound representation of the scattered amplitude, this property holds for an arbitrary texture. Extending previous work pertaining to the more specific K-distributed case (where the texture is Gamma distributed), the authors discuss the error arising during this inference process for a broader range of texture distributions. For three different texture models the authors then derive a condition, on the number of samples over which the phase fluctuations should be averaged, to optimise the extraction of the cross-section. Simulated data assert the viability of their findings. The practical implications of this technique for radar clutters are then discussed. - Author(s): S. Anderson
- Source: IET Radar, Sonar & Navigation, Volume 4, Issue 2, p. 195 –208
- DOI: 10.1049/iet-rsn.2009.0119
- Type: Article
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The interpretation of HF surface wave radar echoes is carried out, implicitly or explicitly, in the context of a physical model of the observation process on whose validity the verisimilitude of the interpretation depends. Hitherto it appears to have been near-universal practice to assume that the signal incident on any spatial cell being interrogated is a scaled, delayed version of the transmitted signal, arriving along the geodesic connecting the location of the transmitter with that of the cell. In this study, the authors describe a model that takes into account the changes to the radar signal as it propagates across the moving sea surface and show that the resulting redistribution of signal energy over the time delay, Doppler and direction-of-arrival dimensions can deviate markedly from that assumed by the idealised model. The authors investigate the dependence of the redistribution on radar and environmental parameters and provide what they hope will be useful guiding principles which can be employed to circumvent, or at least minimise, the short-comings of existing designs. - Author(s): L. Rosenberg ; D.J. Crisp ; N.J. Stacy
- Source: IET Radar, Sonar & Navigation, Volume 4, Issue 2, p. 209 –222
- DOI: 10.1049/iet-rsn.2009.0096
- Type: Article
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209
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Robust maritime surveillance with radar requires an accurate description of the backscatter from the sea. An estimated probability distribution of the backscatter is commonly used to determine the threshold for separating targets from clutter at a given false alarm rate. Data collected at medium to high grazing angles by the Defence Science Technology Organisation (DSTO) Ingara fully polarimetric X-band radar demonstrate that the commonly used K-distribution is not always adequate for modelling the probability distribution. This is especially the case for the horizontal polarisation and in regions of high backscatter where target detection can be a problem. An alternative proposed as a more accurate model in this region is known as the KK-distribution. The analysis presented in this study describes this model with the addition of multiple looks and a thermal noise component to produce greater accuracy in the mean and underlying shape. The threshold required to achieve a constant false alarm rate is then studied and compared with the K-distribution. - Author(s): Y. Dong and D. Merrett
- Source: IET Radar, Sonar & Navigation, Volume 4, Issue 2, p. 223 –238
- DOI: 10.1049/iet-rsn.2009.0082
- Type: Article
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The authors conducted a sea clutter trial using a DSTO (Defence Science and Technology Organisation, Australia) built, vertically polarised, L-band, 16-channel receive array during May 2008, at Kangaroo Island, South Australia. This study reports various properties of sea clutter which the authors measured including the backscatter coefficient, spatial and temporal correlations, distributions and Doppler spectra. Observed phenomena are explained. Techniques for calibrating the collected data are also presented. - Author(s): M. Greco ; P. Stinco ; F. Gini
- Source: IET Radar, Sonar & Navigation, Volume 4, Issue 2, p. 239 –250
- DOI: 10.1049/iet-rsn.2009.0088
- Type: Article
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In recent times, considerable advances have been made on analysing low grazing angle radar sea clutter in the gigahertz frequency range. In this work, a set of coherent and polarimetric sea clutter data is analysed focusing on the statistical and spectral properties of the spikes, whatever is the physical phenomenon that generates them. Using three sea spike defining parameters, the spike amplitude, the minimum spike width and the minimum interval between spikes, it is possible to identify the spiking events from the background. This work shows a sample of results from a statistical and spectral analysis of a set of sea spikes selected from the radar returns, focusing on their Doppler properties, the spike duration and the temporal interval between spikes. - Author(s): S. Anderson and J. Morris
- Source: IET Radar, Sonar & Navigation, Volume 4, Issue 2, p. 251 –264
- DOI: 10.1049/iet-rsn.2009.0095
- Type: Article
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The wide variability of sea surface conditions is reflected in a corresponding variability in sea clutter characteristics; moreover, these characteristics manifest a strong dependence on radar parameters such as frequency, waveform and polarisation. Ideally, radar systems should adapt their parameters to the prevailing sea conditions and viewing geometry so as to optimise performance. In practice this is seldom done, in large part because most radar systems have very limited capability to adapt, but also because the rules that might guide the adaptation process are not yet clearly established. Where an appreciable change in radar parameters or viewing geometry would yield only a slight change in clutter severity and a commensurately modest improvement in radar performance, there is little incentive to adapt. On the other hand, if there are sharp transitions in clutter properties as some radar parameter is varied, then exploitation of the transition may be highly advantageous. This study presents the results of a search for transitions in polarimetric X-band sea clutter, focusing on the dependence on scattering geometry. Experiments were conducted to study clutter variation with elevation angle and azimuth with respect to wind direction. The results demonstrate that transitions exist, that they can be surprisingly sharp, and that the consequences for target detectability may be significant. - Author(s): T. Lamont-Smith ; M. Mitomi ; T. Kawamura ; T. Waseda
- Source: IET Radar, Sonar & Navigation, Volume 4, Issue 2, p. 265 –279
- DOI: 10.1049/iet-rsn.2009.0072
- Type: Article
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Laboratory radar measurements at low grazing angle of long waves of different steepness in the presence of wind waves were examined. The radar cross-section (RCS) variation was found to agree closely with the composite model. The effect of the orbital velocity of the long waves was observable in the Doppler spectra and could be used to determine the wave height; however, other aspects of the Doppler spectra could not be satisfactorily explained by the composite model. Electromagnetic (EM) scattering results were also generated using the Forward-backward code in conjunction with a two-dimensional hydrodynamic code that produced time-dependent wave profiles of long waves with wind blown ripples. The numerical results showed close agreement with the normalised RCS calculated from Bragg scattering theory, σ0=|B|2, but not with the composite model. - Author(s): H.D. Griffiths ; W.A. Al-Ashwal ; K.D. Ward ; R.J.A. Tough ; C.J. Baker ; K. Woodbridge
- Source: IET Radar, Sonar & Navigation, Volume 4, Issue 2, p. 280 –292
- DOI: 10.1049/iet-rsn.2009.0124
- Type: Article
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Bistatic radar is a subject of considerable present interest. Despite this, current understanding of the properties of bistatic clutter, and in particular, bistatic sea clutter, is limited at best. The purpose of this study is to present an analysis of the limited existing published radar data and to derive an empirical model, which expresses the variation of mean σ0 with the measurement geometry and sea conditions. This empirical model is then compared with electromagnetic (EM) scattering calculations using the composite model (sometimes called the two-scale model) to show the extent to which the EM model is able to reproduce the trends observed in the data. The results indicate where improvements to bistatic EM modelling are required (very low grazing angles and out-of-plane scattering), and a general need for more radar data to extend the empirical σ0 model and expand it to the bistatic clutter statistics. - Author(s): R. Douvenot and V. Fabbro
- Source: IET Radar, Sonar & Navigation, Volume 4, Issue 2, p. 293 –301
- DOI: 10.1049/iet-rsn.2009.0073
- Type: Article
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The principle of ‘refractivity from clutter’ (RFC) is to invert the radar sea clutter data to retrieve the refractive index conditions in the low troposphere. This method enables to foresee radar coverage especially in the presence of abnormal refractive conditions. First, this study introduces a new formulation of the radar equation and clarifies the physical hypotheses applied in RFC. This formulation takes into account the sea clutter variations because of the grazing angle variations at very low angle and the refraction effects in one single term. This work also focuses on the analysis of results obtained using the real time ‘improved best fit’ (IBF) inversion method for RFC. The latter is summarised and discussed with main attention on the reliability of the inverted data and on their relevancy with respect to the prediction of radar coverage. - Author(s): C.P. Banahan ; D. Perks ; C. Baker ; K. Woodbridge
- Source: IET Radar, Sonar & Navigation, Volume 4, Issue 2, p. 302 –314
- DOI: 10.1049/iet-rsn.2009.0057
- Type: Article
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The performance of displaced phase centre antenna (DPCA), adaptive DPCA (ADPCA) and joint domain localised space time adaptive processing (JDL-STAP) was examined when applied to data that were not gathered for ground moving target indication (GMTI) purposes, and using very few array elements. Three different methods to be applied at the pre-processing stage to match pulses from different spatial channels were compared. The ADPCA method was shown to be the most robust in the presence of signals leaked from other range cells while traditional DPCA proved to be the most effective at attenuating stationary targets in non-ideal conditions, providing that pre-processing, using a pulse shift and a ramp in phase, was applied to the data. Quantitative results are presented, which are drawn from real experiments using real airborne radar data and which provide a valuable insight into the tolerance of DPCA, ADPCA and STAP when put to use with few spatial channels on non-ideal data. The study shows that all three GMTI algorithms used with few antenna elements can successfully resolve moving targets from clutter in such data and discusses the limitations of each in suppressing unwanted stationary peaks. - Author(s): R. Vicen-Bueno ; M. Rosa-Zurera ; M.P. Jarabo-Amores ; R. Gil-Pita
- Source: IET Radar, Sonar & Navigation, Volume 4, Issue 2, p. 315 –328
- DOI: 10.1049/iet-rsn.2009.0080
- Type: Article
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This study presents the problem of detecting known targets (Swerling 0 model) in simulated ground clutter (land cultivated). As a modelled low-resolution coherent radar system is used, the clutter is modelled by a complex-valued time-correlated Weibull distribution. The research exposed in this study looks for two objectives. First, finding a detection scheme that permits the final user (radar operator) determine if a target is present or not, and its position, size and shape. And second, designing a detection scheme as robust as possible against clutter and target condition changes and approximating the specification and measurement of the radar performance by using clutter models. However, these tasks are really complicated, because high-level clutter echoes are received. A detection scheme based on neural networks is proposed, where feedforward multilayer perceptrons are used. The performance obtained with this detection scheme is discussed from subjective (visual analysis of the achieved detection scans) and objective (receiver operating characteristics) points of view. Finally, this scheme is compared with a coherent detector commonly used when Weibull-distributed clutter is present, the target sequence known a priori detector. This comparison empirically demonstrates the performance improvement achieved by the proposed detector comparing with the commonly used.
Editorial: Radar clutter
Use of sea clutter models in radar design and development
Accurate K-distributed clutter model for scanning radar application
Simulation of coherent sea clutter
Clutter modelling for space–time adaptive processing in airborne radar
Inference of a generalised texture for a compound – Gaussian clutter
Multiple scattering of HF surface waves: implications for radar design and sea clutter interpretation
Analysis of the KK-distribution with medium grazing angle sea-clutter
Analysis of L-band multi-channel sea clutter
Identification and analysis of sea radar clutter spikes
Transitions in the polarimetric radar scattering properties of the sea surface
Electromagnetic scattering from wind blown waves and ripples modulated by longer waves under laboratory conditions
Measurement and modelling of bistatic radar sea clutter
On the knowledge of radar coverage at sea using real time refractivity from clutter
GMTI clutter cancellation using real non-ideal data
Automatic target detection in simulated ground clutter (Weibull distributed) by multilayer perceptrons in a low-resolution coherent radar
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