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Radar, Sonar and Navigation, IEE Proceedings -

Issue 4 • Date 1 Aug. 2003

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Displaying Results 1 - 18 of 18
  • Analysis of micro-Doppler signatures

    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (343 KB)  

    Mechanical vibration or rotation of a target or structures on the target may induce additional frequency modulations on the returned radar signal which generate sidebands about the target's Doppler frequency, called the micro-Doppler effect. Micro-Doppler signatures enable some properties of the target to be determined. In the paper, the micro-Doppler effect in radar is introduced and the mathematics of micro-Doppler signatures is developed. Computer simulations are conducted and micro-Doppler features in the joint time-frequency domain are exploited View full abstract»

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  • X-band wideband experimental airborne radar for SAR, GMTI and maritime surveillance

    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (435 KB)  

    Defence Research and Development Canada - Ottawa has completed Phase I in the development of a new multimode X-band wideband experimental airborne radar (XWEAR) to support studies in synthetic aperture radar (SAR) imaging, inverse SAR (ISAR), ground moving target indication (GMTI) radar and maritime surveillance radar with particular focus on small target detection and long-range surface surveillance. Specific areas of interest include research into SAR imaging techniques for fixed and moving targets, time-frequency analysis of ocean and land moving targets, space-time adaptive processing for application to GMTI, investigation into the electromagnetic backscatter properties of the ocean surface, generation of signatures for automatic target recognition and feature extraction, and analysis on the immunity of wide bandwidth systems against electronic countermeasures. Phase I culminated with the flight trialling of the SAR and maritime surveillance modes. Phase II will see the trialling of the wide area surveillance GMTI (WAS GMTI) and integrated SAR-GMTI modes. A description of the experimental radar is given along with an overview of its data collection capability. Distinguishing features include operation at X-band, single-channel operation for SAR and maritime surveillance, and two-channel operation for WAS-GMTI and integrated SAR-GMTI. The new radar maximises the use of an existing digital scan converter as a controller, and commercially available components including the transmitter, A/D converters and computer boards. The timing circuitry, waveform generator, single- and dual-channel receivers are custom built View full abstract»

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  • Application of adaptive chirplet representation for ISAR feature extraction from targets with rotating parts

    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (494 KB)  

    The problem of feature extraction from inverse synthetic aperture radar (ISAR) data collected from targets with rotating parts is addressed. In traditional ISAR imaging, rigid-body motion is usually assumed. When non-rigid-body motions are present, it is not possible to obtain a focused image of both the target and the rotating part. To solve this problem, the radar signal is first parameterised using the adaptive chirplet signal representation. The signal from the body and that from the rotating part are then separated in the parameter space. Point-scatterer simulation results show that better geometrical features of the body and better micro-Doppler features of the rotating part can be extracted after the separation. The algorithm is also demonstrated using the measurement data from an in-flight aircraft and a walking person View full abstract»

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  • Atomic decomposition-based radar complex signal interception

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    Atomic decomposition (AD) extracting the time-frequency characteristics of signals has been investigated in the frame of complex radar signal detection and classification. AD uses the chirplet dictionary to obtain high-resolution time-frequency representations. Significant improvements on previous AD algorithms have been introduced to increase the detection performance (dictionary extension) and to overcome the resolution problems of AD (greediness detector). An interception receiver based on AD has been analysed and characterised. It is composed of a two-stage scheme: detection of signal components through an AD-based detector, and modulation classifier using AD as a feature extractor View full abstract»

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  • High-resolution time-frequency distributions for manoeuvring target detection in over-the-horizon radars

    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (385 KB)  

    A novel high-resolution time-frequency representation method is proposed for source detection and classification in over-the-horizon radar (OTHR) systems. A data-dependent kernel is applied in the ambiguity domain to capture the target signal components, which are then resolved using root-MUSIC based coherent spectrum estimation. This two-step procedure is particularly effective for analysing a multicomponent signal with time-varying complex time-Doppler signatures. By using the different time-Doppler signatures, important target manoeuvring information, which is difficult to extract using other linear and bilinear time-frequency representation methods, can be easily revealed using the proposed method View full abstract»

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  • Application of adaptive joint time-frequency algorithm for focusing distorted ISAR images from simulated and measured radar data

    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (362 KB)  

    An adaptive joint time-frequency algorithm has been applied and evaluated for focusing distorted ISAR (inverse synthetic aperture radar) images when the target motion is confined to a two-dimensional plane. It is shown that the adaptive joint time-frequency algorithm provides an effective method of achieving rotational motion compensation for ISAR imaging. Examples provided demonstrate the effectiveness of the adaptive joint time-frequency algorithm with both simulated and experimental ISAR data. Results show that if a target is moving smoothly, standard motion compensation generates a clear image of the target by using the conventional Fourier transform methods. However, when a target performs complex motion such as perturbed random motions, standard motion compensation is not sufficient to generate an acceptable image. In this case, the adaptive joint time-frequency algorithm provides an efficient candidate to resolve the image smearing caused by the time-varying behaviour and leads to a well focused ISAR image when the target motion is confined to a two-dimensional plane. The study also adds insight into the distortion mechanisms that affect the ISAR images of a target in motion View full abstract»

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  • Micro-Doppler analysis of vibrating targets in SAR

    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (446 KB)  

    Vibrating targets cause phase modulation of the azimuth phase history for a SAR system. The phase modulation may be seen as a time-dependent micro-Doppler frequency. It is useful to analyse such signals with Cohen's (1995) class time-frequency methods due to their superior resolution potential. The method must be chosen with care, as the effective time integration window of the kernel should not be longer than about a cycle of the modulation signal. Using the adaptive optimal kernel method (AOK), the authors obtained good results from a controlled experiment where two oscillating corner reflectors were placed within a SAR scene collected by the US Navy APY-6 radar. The oscillation frequency and amplitude were calculated from the time-frequency distributions and the results agree well with available ground truth. To resolve the instantaneous frequencies, the kernel time extent had to be sufficiently short View full abstract»

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  • Distortion in the inverse synthetic aperture radar (ISAR) images of a target with time-varying perturbed motion

    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (443 KB)  

    Large distortion in ISAR images of a moving target has been investigated and demonstrated under controlled experiments. The distortion is a result of small time-varying perturbed motion experienced by the target and is attributed to a modulation effect in the phase of the radar return from the target. The Doppler motion of the target, modulated by a time-varying perturbation, results in a broad smear in the phase of the radar signal. A numerical model of the distortion based on the phase modulation effect has been developed. Simulated ISAR images produced by this model are in good agreement with experimental results. The numerical and experimental studies described provide a better understanding of the distortion mechanism that affects the ISAR images of a target in motion View full abstract»

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  • Effect of nonuniform target motion on radar backscattered waveforms

    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (281 KB)  

    The effect of nonuniform motion on radar waveforms is discussed. By considering the physical model of a perfectly reflecting mirror with an arbitrary law of motion r(t), it is possible to determine the functional form of the scattered wave at the receiver for any waveform in general. The particular example of an interrupted continuous wave waveform is used to analyse the effect of nonuniform motion on the return spectrum. These models provide a theoretical foundation for the observations of micro-Doppler that have been discussed by a number of authors. Finally, some of the implications, both physical and mathematical, of nonuniform motion for time-frequency methods are addressed View full abstract»

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  • Assessment of chaos-based FM signals for range-Doppler imaging

    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (558 KB)  

    The authors analysed a set of random frequency modulated (FM) signals for wideband radar imaging and assessed their resolution capability and sidelobe distribution on the range-Doppler plane. To this effect deterministic, bounded, nonlinear iterated maps were first considered. The initial condition of each chaotic map was assigned to a random variable to obtain statistically independent samples with invariant probability density function. The resulting sequences, which have white time-frequency representations, are used to construct wideband stochastic FM signals. These FM signals are ergodic and stationary. The autocorrelation, spectrum and the ambiguity surface associated with each of the FM signals were characterised. It was also demonstrated that the ambiguity surface of an FM signal generated via a chaotic map with uniform sample distribution and tail-shifted chaotic attractor is comparable to the ambiguity function of a Gaussian FM signal View full abstract»

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  • Time-frequency analysis for plastic landmine detection via forward-looking ground penetrating radar

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    Time-frequency analysis techniques are used for buried plastic landmine detection with a forward-looking ground penetration radar (GPR) system. Several time-frequency distributions are considered to characterise and interpret the scattering phenomena of both targets and clutter. An ambiguity function based detector is also presented, which employs principal component analysis and feature selection for data dimensionality reduction and linear discriminant analysis for signal classification. Experimental results based on the SRI (Stanford Research Institute) experimentally measured forward-looking GPR data are presented, showing a significant detection performance improvement over the conventional detector View full abstract»

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  • Wide-angle radar imaging using time-frequency distributions

    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (475 KB)  

    Low-frequency radar systems provide some attractive advantages in a few niche applications, such as foliage penetration and covert operation. In low-frequency imaging systems, data must be collected over a wide range of angles to obtain cross-range resolution comparable to that obtainable from a competing small-angle high-frequency system. The reflectivity of a target varies with aspect angle; although this variation is usually ignored by traditional radar imaging algorithms, it sometimes cannot be neglected in wide-angle scenarios. To account for aspect dependence of reflectivity, time-frequency transforms have been invoked to generate a series of images corresponding to different look angles; these images may be considered individually or synthesised into a single image. A simple theoretical analysis with a point scatterer illustrates why the angular dependence needs explicit consideration. The potential of time-frequency methods is illustrated via simulations View full abstract»

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  • Super-resolution Fourier transforms by optimisation, and ISAR imaging

    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (268 KB)  

    5A method for super-resolution ISAR imaging, denoising, and error estimation is developed using a novel Fourier transform that exploits the a priori information that the image is sparse, i.e. contains relatively few bright points. The method applies nonlinear optimisation to the complex-valued pixels to estimate the image by minimising its l1-norm. Noiseless images require linear programming, while quadratic programming with logarithmic barriers is necessary when complex-valued Gaussian noise is present. The novel Fourier transform, which is referred to as the l1-FFT, works with 'missing' data points, making 'jackknife' estimates of the mean and variance of each pixel value possible. These estimates should aid in image classification. This work extends earlier work of Chen, Donoho and Saunders on basis pursuit and denoising to complex signals, by formulating and solving the corresponding complex-valued nonlinear optimisation problems View full abstract»

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  • Manoeuvring target detection in over-the-horizon radar using adaptive clutter rejection and adaptive chirplet transform

    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (534 KB)  

    In over-the-horizon radar (OTHR) systems, the signal-to-clutter ratio (SCR) used for moving target detection is very low. For slowly moving targets such as ships, the SCR is typically from -50 dB to -60 dB and their Doppler frequencies are close to that of the clutter. For manoeuvring targets, such as aircraft and missiles, the Doppler frequencies are time-varying when a long integration time is considered. When a target does not move uniformly, the Fourier transform based target detection techniques, including super-resolution spectrum techniques, may fail to work appropriately. In such situations, the Doppler signatures are time-varying and, therefore, time-frequency analysis techniques can be used for manoeuvring target detection. In addition, clutter rejection is also required for target detection due to the low SCR. The existing adaptive clutter rejection algorithms combine clutter rejection with spectrum analysis methods, which usually assume uniformly moving target (i.e. sinusoidal Doppler signature) models. An adaptive clutter reject algorithm is proposed together with the adaptive chirplet transform technique for manoeuvring target detection in a multipath environment. Simulation results using a simulated manoeuvring target signal with received raw OTHR clutter data show that targets with SCR below -50 dB can be detected by using the proposed algorithm View full abstract»

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  • Wavelet-RELAX feature extraction in radar images

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    In classical high-frequency radar imaging, like synthetic aperture radar imaging, man-made target contributions are often well described by decomposing their signature into a set of bright points. The basic model supposes that these elementary reflectors are independent of the relative angular aspect and of the observation frequencies. Many feature extraction methods, such as CLEAN/RELAX-based algorithms, are built on this hypothesis and so it is currently used in assisted/automatic target recognition algorithms (ATR). However, this simple model cannot describe the variability of the signatures one can observe in image databanks. The authors propose extending the target feature extraction capacities of the CLEAN/RELAX algorithm to dispersive scatterers using generalised wavelets View full abstract»

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  • ISAR motion compensation using evolutionary adaptive wavelet transform

    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (336 KB)  

    Many time-frequency analysis techniques have been used for ISAR motion compensation. One of them, the adaptive wavelet transform (AWT), is cross-term free and has high resolution, but its accuracy is limited because it uses a bisection search method and fast Fourier transform (FFT) for parameter extraction. A novel time-frequency (T-F) analysis, called the evolutionary adaptive wavelet transform (EAWT), is used for ISAR motion compensation. The EAWT is more accurate than the conventional AWT. Using artificially created data from three time-frequency centres and simulated MIG-25 ISAR data, this algorithm is compared with the conventional AWT for accuracy. From the constructed ISAR image using AWT and EAWT, it is demonstrated that the EAWT algorithm can obtain a more clear motion-compensated ISAR image than the conventional AWT View full abstract»

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  • Analysis of SAR images by multidimensional wavelet transform

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    The description and development are described of a multidimensional continuous wavelet transform for synthetic aperture radar (SAR) image analysis, especially for the analysis of 'dispersive' reflectors located on a ground illuminated by a SAR. The usual imaging process makes the assumption that the reflectors are isotropic (i.e. that they behave the same way regardless of the angle from which they are viewed) and white (they have the same properties within the emitted frequency bandwidth). New imaging capacities (offering large bandwidth, low band and large angular excursions of analysis, for example) make these assumptions obsolete. The goal is to present methods based on the multidimensional continuous wavelet transform which highlight these effects for target recognition or identification. Some examples of this analysis are given by processing real data collected in X-band by the RAMSES airborne SAR facilities at ONERA 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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