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Radar, Sonar & Navigation, IET

Issue 1 • Date February 2010

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Displaying Results 1 - 13 of 13
  • Editorial

    Page(s): 1
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (63 KB)  

    As is the way with many things, the performance of this journal is monitored and assessed by various metrics, and it is pleasing to note that almost all of these are improving steadily. The impact factor increased by 24% in 2009, giving the journal its highest figure (0.715) for at least 6 years. View full abstract»

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  • Sea trials of an underwater, ad hoc, acoustic network with stationary assets

    Page(s): 2 - 16
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1019 KB)  

    The diverse roles of deployable underwater assets have increased the need for ad hoc networking capability. This capability is defined as the ability to form acoustic communication links by deploying assets in a non-deterministic manner, without depending on a priori route and positioning information. Each asset represents a node in the network, and can act as a data source, sink or router, and initiates, stores or relays data, respectively. Data packets may be hopped over a few nodes before arriving at the designated destination. This ad hoc network consists of two main layers: the medium access control (MAC) layer to resolve node contention, and the ad hoc routing layer to manage routing information. In the MAC layer, both random access and time-division protocols are applied. The protocol in the routing layer is responsible for route setup and route maintenance. This concept of multiple-hop, ad hoc networking was implemented during sea trials conducted in Portland Harbour, UK, involving up to six nodes. The trial was designed with the aim of gaining application experience in ad hoc network deployment and in assessing the performance of the protocols in a real operating environment. The emphasis was on modem integration, and the stability and reliability of packet transport. The trial results and their subsequent analysis demonstrated the robustness of the network in performing ad hoc routing and resolving node contention in a realistic and acoustically challenging environment. View full abstract»

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  • Motion feature extraction for stepped frequency radar based on Hough transform

    Page(s): 17 - 27
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (418 KB)  

    The high resolution range profile can be obtained through coherent pulse compression processing in every coherent processing interval (CPI) for stepped frequency radars (SFR). The radar observation time can be divided into multiple CPIs. By utilising the temporal information inherent to a sequence of these range profiles, a time-range image containing the target motion information can be synthesised. Through analyses of the point scatterer targets with the radial uniform motion, radial uniformly accelerated motion, rotation and vibration, this study indicates that there is a certain correlation between the target motion features and the time-range image features in the limited observation time. Based on this result, we propose a motion feature extraction method for SFR without any assistant information using the conventional and well-known feature extraction tool, Hough transform. The authors give detailed analyses and explanation of this method, and verify them by outfield experiments, demonstrate the motion feature extraction results using real radar data. The proposed method enables the motion feature extraction through space non-coherent integration, which fully utilises the radar data information under low signal-to-noise ratio conditions. View full abstract»

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  • MIMO-OFDM radar for direction estimation

    Page(s): 28 - 36
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (315 KB)  

    Multiple-input-multiple-output (MIMO) radar makes use of orthogonal signals to obtain the phase delay for each transmitting/receiving antenna pair, and thus increasing the accuracy of direction estimation. The previously proposed MIMO radar assumes narrowband signals that guarantee the waveform orthogonality during the signals- transmission, propagation and reception. However, a narrowband system is unstable in target localisation because of the fluctuation of the target-s radar cross section. An MIMO-OFDM radar is proposed for target localisation. It adopts the OFDM technique to simultaneously transmit and receive a set of multiple narrowband orthogonal signals at orthogonal frequencies. A practical model accommodating a physical target is presented to simulate the MIMO-OFDM radar. As an example, a composite target composed of five infinite dielectric cylinders is localised by a four-element uniform linear array. The performance of the MIMO-OFDM radar is investigated by examining the estimation error for different numbers of sub-bands, different signal-to-noise ratios and different target directions. It is demonstrated by simulation that the MIMO-OFDM radar gives more statistically stable estimation by spreading the signal power over a wider spectrum. View full abstract»

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  • Performance analysis of ordered-statistic greatest of-constant false alarm rate with binary integration for M-sweeps

    Page(s): 37 - 48
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (844 KB)  

    The performance of the ordered-statistic greatest of (OSGO) constant false alarm rate (CFAR) scheme with binary integration for M non-coherent sweeps in Weibull background was investigated for homogeneous and non-homogeneous backgrounds, with an assumption of known shape parameter. This kind of processing is based on the fact that the clutter can be segmented in regions in many real radar scenarios where a time-varying two-parameter distribution function family can be fitted, but the clutter power may vary locally inside the region. Under the assumption of known shape parameter, the authors examined the changes of the false alarm rate and detection probability of the OSGO-CFAR with binary integration when the shape parameter differs from the nominal one, and compared them to those of the OSGO-CFAR with single pulse processing. The authors have derived analytic expressions of the detection probability and false alarm rate during clutter power transitions for the OSGO-CFAR with binary integration in Weibull background. It is shown that the OSGO-CFAR with binary integration can not only improve the detection performance significantly, but it also control the rise of the false alarm rate at clutter edges more effectively compared to the OSGO-CFAR with single pulse processing. Moreover, it exhibits a good immunity to the variation of the shape parameter. View full abstract»

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  • Acquisition of satellite navigation signals using dynamically chosen measurements

    Page(s): 49 - 61
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (811 KB)  

    A new approach to sequential acquisition of satellite navigation signals is presented where the collection of measurement statistics is steered dynamically during the acquisition process. The process consists of a fixed number of operation cycles during which the state of the receiver is maintained as a vector of conditional probabilities of acquisition hypotheses, each hypothesis being associated with a code delay and a Doppler frequency. During each operation cycle, one hypothesis is singled out by applying a suitable policy on the state vector. The down-converted satellite signal is then despread and frequency shifted according to the hypothesis. The resulting signal is integrated and squared to form a statistic that is used to update the state vector according to Bayes' theorem. After completing the cycles, a decision is made in favour of the hypothesis corresponding to the highest posterior probability. Two policies are investigated, one based on the maximisation of one-step posterior probability and the other based on the maximisation of information gain. Simulation results are presented indicating that the proposed approach provides a significant performance advantage over standard techniques for a wide range of signal-to-noise ratios. View full abstract»

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  • Model-based sea mine classification with synthetic aperture sonar

    Page(s): 62 - 73
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1204 KB)  

    The quality and effectiveness of sensor information provided by mine-hunting autonomous underwater vehicles (AUVs) equipped with high-resolution sonars has improved drastically in recent years. In parallel, data rates have significantly increased resulting in information overload. Automatic target recognition (ATR) is regarded as a solution for this problem. This study describes a specific ATR technique based on model matching for application to high-resolution data. A sonar model for generation of high-resolution synthetic aperture sonar (SAS) images is described and applied both as database generator and classification. The performance of the model matching, which is attained by correlation and stochastically, is evaluated using a large data set covering the variety expected in mine-hunting operations. The model-based features generated in this way are able to reach an acceptable classification performance. The article is concluded with one real data example, which is easily classified when training with the simulated database. Further work is next aimed to confirm performance on real data. View full abstract»

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  • Extending Loffeld's bistatic formula for the general bistatic SAR configuration

    Page(s): 74 - 84
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (689 KB)  

    This study derives an accurate bistatic point target reference spectrum based on a zeroth-order polynomial model. The spectrum contains only two hyperbolic square root terms that are very analogous in form to the analytical monostatic spectrum. The new formulation can be considered as an improvement of the Loffeld's bistatic formula (LBF) and allows it to handle a wider range of bistatic configurations. The original LBF works well only in the case where the contributions of transmitter and receiver to the total Doppler modulation are approximately equal. An earlier paper on the extended LBF (EBLF) uses time bandwidth product (TBP) to weight the azimuth phase modulation from each platform. However, this extension is valid only in the low squint bistatic geometry. Both LBF and ELBF are expanded up to the quadratic term to derive an approximate bistatic spectrum; however, they do not show a good focusing performance in the more complex bistatic geometry, for example, the high squint case. This is due to the inaccurate individual time-Doppler correspondences. In this study, a norm in Euclidean space is defined to derive the optimal individual time-Doppler correspondences. Using the accurate individual time-Doppler correspondences, a zeroth-order polynomial model can be used to readily derive a more accurate bistatic spectrum. Two simulation experiments in the high squint geometry are used to verify the accuracy of this new formulation. The first experiment uses a parallel-track spaceborne/spaceborne configuration, and the second experiment involves an orthogonal-track airborne/airborne case. View full abstract»

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  • Experimental research of unsupervised Cameron/maximum-likelihood classification method for fully polarimetric synthetic aperture radar data

    Page(s): 85 - 95
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (4680 KB)  

    In this study, experimental research on classification is applied to fully polarimetric data in X-band from China. Considering the amplitude and phase error between H and V channels in the system, the authors firstly correct the error in original data. The authors also deduce the formula of Cameron's classification method for the real data in our study. Then Cameron's method is used to initially classify the site image. Finally, the initial classification map defines training sets for the maximum-likelihood (ML) classifier. The advantages of this method are the automated classification and interpretation of each class based on the scattering mechanism. The experiment demonstrates the feasibility of the proposed approach, which dramatically improves the X-band data classification result compared with the Cameron method and H/??/ML method. View full abstract»

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  • Automatic algorithm for inverse synthetic aperture radar images recognition and classification

    Page(s): 96 - 109
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (883 KB)  

    The authors propose an algorithm for automatic aircraft categories that is models classification from inverse synthetic aperture radar (ISAR) images that use pulse reflection shape and Doppler shifts of parts of aircraft that are in any maneuver that introduces rotation to the target. The authors artificially generated five different categories of ISAR aircraft using computer simulations and tested these simulated ISAR aircraft images of the airplanes defined by size and shape that are flying in a prescribed holding pattern. The authors investigate in what parts of the holding pattern the ISAR reflections provide information that makes it possible to identify to which of the five categories an aircraft in the holding pattern belongs. The obtained results show that it is possible in most parts of the holding pattern to successfully classify the various aircraft targets. View full abstract»

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  • Problem of signal synchronisation in space-surface bistatic synthetic aperture radar based on global navigation satellite emissions - experimental results

    Page(s): 110 - 125
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1844 KB)  

    This study presents the synchronisation problem in `space-surface bistatic synthetic aperture radar (SS-BSAR)` system. Global Navigation Satellite Systems (GNSS) are considered as transmitters of opportunity. It highlights various important issues of synchronisation, specifically related to SS-BSAR utilising GLONASS as the transmitter. Experimental testing of the synchronisation algorithm is described and verified using the GLONASS satellite. Also, experimental images obtained from GLONASS are presented and briefly analysed. View full abstract»

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  • Stealth technology for wind turbines

    Page(s): 126 - 133
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (578 KB)  

    Currently, a large proportion of proposed UK wind farms have either concerns raised at the pre-planning stage or formal objections made by radar operators on the basis of the potential for wind turbines to cause interference to radar systems. The current generation of on and off-shore three-bladed horizontal axis wind turbines have radar signatures consistent with their often very large physical size and hence considerable potential to reduce the ability of ground-based radars to detect targets in the vicinity of the farm. The impact of wind farms, particularly on ground-based aviation radars such as those operated for air defence and military and civil air traffic control purposes is likely to become particularly acute as European Union member governments strive to meet the requirements for energy generation under the Renewables Obligation. In addition, the increasing number of offshore wind farm projects proposed has the potential to cause interference to marine radars such as coastal vessel traffic services and those on-board vessels for navigational purposes. This study considers the options available for the reduction of turbine radar signature and presents solutions for each of the main external turbine components. The radar signature reduction approaches are based on existing technologies developed for aerospace stealth applications. However, the realisation of these for the purposes of reducing wind turbine radar signatures is a novel development, particularly in the solutions proposed. The reduction of wind turbine-induced radar interference is a growing area of research. View full abstract»

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  • Huber-based unscented filtering and its application to vision-based relative navigation

    Page(s): 134 - 141
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (411 KB)  

    A new algorithm called Huber-based unscented filtering (UF) is derived and applied to estimate the precise relative position, velocity and attitude of two unmanned aerial vehicles in the formation flight. The relative states are estimated using line-of-sight measurements between the vehicles along with acceleration and angular rate measurements of the follower. By making use of the Huber technique to modify the measurement update equations of standard UF, the new filtering could exhibit robustness with respect to deviations from the commonly assumed Gaussian error probability, for which the standard unscented filtering would exhibit severe degradation in estimation accuracy. Furthermore, contrast to standard extended Kalman filtering, more accurate estimation and faster convergence could be achieved from inaccurate initial conditions. During filter design, the global attitude parameterisation is given by a quaternion, whereas a generalised three-dimensional attitude representation is used to define the local attitude error. A multiplicative quaternion-error approach is used to guarantee that quaternion normalisation is maintained in the filter. Simulation results are shown to compare the performance of the new filter with standard UF and standard extended Kalman filtering for non-Gaussian case. View full abstract»

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Aims & Scope

IET Radar, Sonar & Navigation covers the theory and practice of systems involving the processing of signals for radar, radiolocation, radionavigation and surveillance purposes.

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IET Research Journals
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