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Radar, Sonar & Navigation, IET

Issue 5 • Date June 2012

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Displaying Results 1 - 13 of 13
  • Optimal coherent radar detection in a K-distributed clutter environment

    Publication Year: 2012 , Page(s): 283 - 292
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (339 KB)  

    An optimal detector in the sense of generalised likelihood ratio test (GLRT) for coherent radar detection in a compound K-distributed clutter environment is re-studied in detail. A few properties of the detector are derived showing potential of its implementation in radar systems. To the optimal detector, sea spikes (abnormally high radar returns from the sea surface) are unlikely to trigger false alarms, leading to a significant improvement in target detection. Two suboptimal detectors, aiming at saving computational cost, are proposed, and their performance is compared with the GLRT detector. The detector is assessed using true radar sea clutter data, and the problem of sea spikes causing excessive false alarms is identified and discussed. View full abstract»

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  • Fractal characteristic in frequency domain for target detection within sea clutter

    Publication Year: 2012 , Page(s): 293 - 306
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1385 KB)  

    This study mainly describes the fractal property of the frequency spectrum of the sea clutter and the application of the obtained fractal characteristic in frequency domain to the constant-false-alarm-rate (CFAR) target detection within sea clutter. First, this study takes fractional Brownian motion (FBM) for example, and the spectrum of the FBM is proved to be fractal theoretically on condition that the time series of the FBM is fractal. This argument lays the foundation for the application of fractal theory to the frequency spectrum. Next, X- and S-band real radar data are used for the verification of the fractal property of the real sea clutter frequency spectrum. Finally, the effects of the length of the time series and fast Fourier transform (FFT) are analysed in detail. The results show that the frequency spectrum of the real sea clutter is fractal in the statistical sense and the frequency Hurst exponents of clutter range bins and target range bins are distinguishable. Therefore the frequency Hurst exponent is used for the CFAR target detection within sea clutter. View full abstract»

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  • Two-dimensional direction of arrival estimation by exploiting the symmetric configuration of uniform rectangular array

    Publication Year: 2012 , Page(s): 307 - 313
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (447 KB)  

    In this study, a new two-dimensional direction of arrival (2D DOA) estimation method is proposed for a uniform rectangular array (URA). The impinging signals are a mixture of uncorrelated and coherent signals. The method consists of two steps. The DOAs of uncorrelated signals are first estimated by a modified 2D estimation of signal parameters via rotational invariance techniques (ESPRIT). Then the contributions of uncorrelated signals and noises are eliminated after performing a subtraction operation on the elements of the covariance matrix and only those of coherent signals remain. Based on these subtracted elements, a decorrelating matrix with a larger size is constructed to estimate the DOAs of coherent signals. These two-step processes can be carried out in parallel because there is no inherent relationship between them. The proposed method has high estimation precision, needs no 2D angle searching and is suitable for the array no matter whether the number of sensors is odd or even. Simulation results demonstrate the effectiveness and performance of the proposed method. View full abstract»

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  • New waveform for magnetron marine radar - experimental results

    Publication Year: 2012 , Page(s): 314 - 321
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (731 KB)  

    The unambiguous range of a pulse-radar is related to the pulse repetition interval (PRI). Most magnetron-based marine radars adjust the PRI according to the maximum displayed range. They correspondingly adjust the pulse-width (PW) to keep the ratio PW/PRI nearly constant. The extreme settings can be described as `short pulse, short PRI` (SPSP) for short distances and `long pulse, long PRI` (LPLP) for long distances. Such settings keep the transmitter`s duty cycle and the energy-on-target, relatively constant. Penalties of long PW are large clutter area illumination and poor range resolution. Maintaining a short pulse is important in magnetron-based radar, because a magnetron does not lend itself to pulse compression. The study presents a method that allows operating in the SPSP mode for long distances as well. Both theory and experimental results are presented. View full abstract»

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  • Automatic modulation classification of radar signals using the Rihaczek distribution and hough transform

    Publication Year: 2012 , Page(s): 322 - 331
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (587 KB)  

    It is an important work to classify the modulation type of the intercepted radar signal for an electronic intelligence (ELINT) receiver in a non-cooperative environment. The authors use the Rihaczek distribution (RD) and the Hough transform (HT) to concentrate the energy in time-frequency plane and derive two new characteristic features, namely the ratio of the minimum to the maximum of the HT and the peak number of the HT of the real part of the RD, to improve the probabilities of successful recognition (PSRs) to recognise the classical low probability of intercept (LPI) radar signals. The first feature is especially suitable for the linear frequency modulation (LFM), whereas the second one is specifically designed for frequency shift keying (FSK). The choice of thresholds and the effects of signal parameters are analysed. Simulations show that the PSRs can reach 90% when the signal-to-noise ratio (SNR) is above -4 dB. The proposed algorithm is better than the previous algorithms by just using ambiguity function. View full abstract»

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  • ISAR based techniques for refocusing non-cooperative targets in SAR images

    Publication Year: 2012 , Page(s): 332 - 340
    Cited by:  Papers (5)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (922 KB)  

    Non-cooperative moving targets typically appear defocused in synthetic aperture radar (SAR) images as they are non-stationary during the coherent processing interval. Typically, the problem of refocusing moving targets in SAR scenes is addressed as a problem of the target's motion estimation and compensation. In this study, the problem is addressed as a problem of non-cooperative target imaging and the authors propose a solution based on the use of inverse synthetic aperture radar (ISAR) processing to solve this problem. Taking into consideration the advantages of SAR processing, the problem is tackled starting from formed SAR images, where non-cooperative targets images are firstly detected, then backprojected to the received data domain and reprocessed as ISAR data. The effectiveness of the proposed method is then tested on Cosmo-Skymed spotlight SAR data of maritime targets. View full abstract»

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  • Design of task scheduling process for a multifunction radar

    Publication Year: 2012 , Page(s): 341 - 347
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (210 KB)  

    During the operation of the multifunction radar system, all the tasks related to the functions of the radar must be launched. The key element of the radar responsible for managing all these tasks is the task scheduler. Many scheduling techniques give good results at the expense of too complex and expensive designs. This study presents the results of a model for a radar task scheduler to achieve both a simple design and a good performance. The scheduling process consists of three stages in which the whole scheduling is divided into: task priorisation, scheduling algorithm and temporal planning. A task priority method is established to be applied to the tasks and the scheduling algorithms that have been tested based on this criterion for the priority task queue building. The authors have developed a software platform for testing all scheduling algorithms. The evaluation of the schedulers was made based on a set of features of the radar to measure the system's performance from the timing and the tasks execution. The authors offer a model to test the global radar system focusing on the task scheduler. This way allows us to analyse different scheduling algorithms and policies, and applying specifically scheduling policies that give priority to the most important and critical tasks. View full abstract»

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  • Signal mode and imaging algorithn for spaceborne interrupted continuous-wave synthetic aperture radar

    Publication Year: 2012 , Page(s): 348 - 358
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (836 KB)  

    Microsatellites have been developed with onboard equipments to monitor and detect early signs of natural disasters and man-caused destructing emergencies. Continuous-wave (CW) synthetic aperture radar (SAR) system operates at constant low-peak transmission power which offers smaller size and lower cost, and this quality provides an appropriate option for microsatellites in remote-sensing fields that can work in all-weather conditions. However, using two antennas for sending and receiving signal separately will cost much more compared with a single antenna; in addition, it is difficult to achieve the antenna isolation if two separate antennas are used on one platform. Interrupted CW SAR (ICW SAR) uses a single antenna on a single microsatellite to share the signal transmitting and receiving in different time divisions. In this mode, the antenna is switched between sending operation and receiving operation to avoid the isolation problems and reduce the costs. Moreover, ICW SAR can also overcome the long-lasting problem that the range resolution of CW SAR is limited by the slant range of the farthest target of interest, which makes the CW SAR capable of long-distant sensing and detection for the first time. This makes CW SAR applications feasible in spaceborne remote-sensing fields. However, it will cause sparse aperture when the antenna is switched to sending mode. In this study, an approach is proposed to formulate the relationship of the contiguous ICW SAR data in one range bin based on CW SAR signal model in the two-dimensional time domain. A signal reconstruction algorithm using iteration method is proposed based on this relationship. Simulation experiments show that the proposed method works well to achieve satisfying results under spaceborne ICW SAR mode. Finally, the Wavenumber Domain Algorithm (WDA) is used to focus on the reconstructed ICW SAR data, and the focusing quality of the image agrees well with the theoretical values. It means that the proposed spac- borne ICW model and imaging algorithm can be extended to the future spaceborne applications. View full abstract»

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  • Gaussian mixtures in multi-target tracking: a look at gaussian mixture probability hypothesis density and integrated track splitting

    Publication Year: 2012 , Page(s): 359 - 364
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (263 KB)  

    Multi-target tracking in clutter, assuming linear target trajectory propagation and linear target measurement equation, naturally leads to a Gaussian mixture (GM) target tracking solution. This study examines and compares two prominent methods that use the GMs: the probability hypothesis density and the integrated track splitting. Both are recursive Bayes methods and both incorporate the false track discrimination capabilities. They are represented in the form of GM target density filters. The modelling assumptions are translated in the algorithmic requirements. The authors compare the algorithms on the basis of these requirements with the future work indicated to reconcile algorithms and requirements. View full abstract»

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  • Generic multisensor multitarget bias estimation architecture

    Publication Year: 2012 , Page(s): 365 - 378
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (797 KB)  

    Current bias estimation algorithms for air traffic control (ATC) surveillance are focused on radar sensors, but the integration of new sensors (especially automatic dependent surveillance-broadcast and wide area multilateration) demands the extension of traditional procedures. This study describes a generic architecture for bias estimation applicable to multisensor multitarget surveillance systems. It consists on first performing bias estimations using measurements from each target, of a subset of sensors, assumed to be reliable, forming track bias estimations. All track bias estimations are combined to obtain, for each of those sensors, the corresponding sensor bias. Then, sensor bias terms are corrected, to subsequently calculate the target or sensor-target pair specific biases. Once these target-specific biases are corrected, the process is repeated recursively for other sets of less reliable sensors, assuming bias corrected measures from previous iterations are unbiased. This study describes the architecture and outlines the methodology for the estimation and the bias estimation design processes. Then the approach is validated through simulation, and compared with previous methods in the literature. Finally, the study describes the application of the methodology to the design of the bias estimation procedures for a modern ATC surveillance application, specifically for off-line assessment of ATC surveillance performance. View full abstract»

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  • Some results on characteristics of bistatic high-range resolution profiles for target classification

    Publication Year: 2012 , Page(s): 379 - 388
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (874 KB)  

    This study focuses on the bistatic high-range resolution profiles (HRRPs) of high-speed and manoeuvring targets and considers how to utilise the length of the bistatic HRRP for target classification. The bistatic HRRP of a high-speed and manoeuvring target is obtained via stretch processing and motion compensation, and its distortion caused by target translation is analysed quantitatively. It is demonstrated that the distortion of bistatic HRRPs is quite different from the monostatic case. The conventional length of the bistatic HRRP cannot reflect the target length, as in the monostatic case, so a new length is defined - the bistatic bisector HRRP length - which corresponds to the length of the target-s projection on the bisector of the bistatic angle. Additionally, the sensitivity of the bistatic HRRP to the target aspect and location is discussed and the bistatic bisector HRRP length is proved to be applicable for target classification through computer simulation and electromagnetic calculation. View full abstract»

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  • Adaptive fractional fourier transform-based detection algorithm for moving target in heavy sea clutter

    Publication Year: 2012 , Page(s): 389 - 401
    Cited by:  Papers (7)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1015 KB)  

    Attention has been focused on the moving target detection in heavy sea clutter. On the basis of detection model of moving target with fluctuant amplitudes, a novel adaptive algorithm in fractional Fourier transform (FRFT) domain is proposed, which combines statistic-based and FRFT-based detection method. FRFT has good energy concentration property on linear frequency modulation (LFM) signal with the optimal transform angle, which is determined by calculating spectral kurtosis (SK) in FRFT domain. Grading iterative search method is used for good accuracy of parameter estimation and fast calculation speed. A novel adaptive line enhancer (ALE) in FRFT domain is proposed to suppress sea clutter and improve signal-to-clutter ratio (SCR), which provides less error and faster convergence. Leakage factor is introduced into the update equation of weight vector to reduce `memory effect` and step size is normalised by the power of input signal with better convergence characteristic. In the end, both X-band and S-band real sea clutter is used for verification and the results present that the proposed algorithm has good convergence property and small mean square error (MSE). Weak moving target in low SCR environment (SCR = -6 dB) can be well detected and estimated, which indicates the effectiveness of the algorithm. View full abstract»

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  • Ultra wideband indoor navigation system

    Publication Year: 2012 , Page(s): 402 - 411
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (767 KB)  

    Typical indoor environments contain multiple walls and obstacles consisting of different materials. As a result, current narrowband radio frequency (RF) indoor navigation systems cannot satisfy the challenging demands for most indoor applications. The RF ultra wideband (UWB) system is a promising technology for indoor localisation owing to its high bandwidth that permits mitigation of the multipath identification problem. This work proposes a novel UWB navigation system that permits accurate mobile robot (MR) navigation in indoor environments. The navigation system is composed of two sub-systems: the localisation system and the MR control system. The main contributions of this work are focused on estimation algorithm for localisation, digital implementation of transmitter and receiver and integration of both sub-systems that enable autonomous robot navigation. For sub-systems performance evaluation, statics and dynamics experiments were carried out which demonstrated that the proposed system reached an accuracy that outperforms traditional sensors technologies used in robot navigation, such as odometer and sonar. 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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