By Topic

Radar, Sonar & Navigation, IET

Issue 3 • Date June 2010

Filter Results

Displaying Results 1 - 16 of 16
  • Square-root second-order extended Kalman filter and its application in target motion analysis

    Page(s): 329 - 335
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (470 KB)  

    In this study, a new non-linear filter based on second-order extended Kalman technology and square-root Kalman algorithm is proposed and applied to the problem of target motion analysis (TMA). By orthogonalising the state vectors with the square root of covariance matrix, the authors reduce the computational complexity in the second-order extended Kalman algorithm, and then we deduce a second-order extended Kalman algorithm based on square-root Kalman technology, which is more numerically stable and can guarantee positive and semi-definiteness of the state covariance. The authors apply the new algorithm to a TMA problem, and prove with both numerical simulation and actual experimentation that their algorithm performs well in the significant non-linear systems. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Coherence improving algorithm for airborne multichannel SAR-GMTI

    Page(s): 336 - 347
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1234 KB)  

    The study develops an algorithm to improve coherence for the multichannel airborne along-track synthetic aperture radar (SAR), which can be used for ground moving target indication (GMTI) by comparing two SAR images obtained from different channels. The turbulent aircraft motion, beam pattern difference and frequency response difference that may degrade the coherence are discussed in detail. The aircraft motion error is firstly estimated and corrected based on the range compressed data. After focusing on the beam pattern differences and the receive channel imbalance are compensated using the two two-dimensional (2-D) adaptive filters, the first in the range-Doppler domain and the second in the range-frequency azimuth-time domain. It is shown that using the coherence improving algorithm the coherence of SAR complex image pairs can be improved greatly. The effectiveness of the algorithm is demonstrated with real data acquired by a Chinese X-band multichannel airborne SAR-GMTI system. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Human motion estimation with multiple frequency modulated continuous wave radars

    Page(s): 348 - 361
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1265 KB)  

    Human motion estimation is an important issue in automotive, security or home automation applications. Radar systems are well suited for this because they are robust, are independent of day or night conditions and have accurate range and speed domain. The human response in a radar range-speed-time measurement behaves like an extended target where legs and arms coincide. A mutually non-coherent radar sensor network makes it possible to estimate additional information of the extended target response. To keep the system low cost the network uses commercial off-the-shelf (COTS) radar sensors without synchronisation of frequency or phase between the radar sensors. This article presents the results of human motion estimation with a mutually non-coherent radar sensor network. The calibration, radar processing, parameter estimation and classification of extended human objects are described. The swinging and rotating moving body parts give elliptical shapes in the differential range-speed responses. A model fit gives the legs and arms parameters on which classification is possible. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Time-orthogonal waveform diversity and joint domain localised algorithm for distributed aperture radars

    Page(s): 362 - 374
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (555 KB)  

    Distributed aperture radars represent an interesting solution for target detection in strong interference environments. Distributed apertures provide improved angular resolution or are able to view a target from multiple look-angles, thereby exploiting scintillation. However, because of the large distances between array elements, both target and interfering sources are in the near field of the antenna array. Furthermore, because of the relative motion between antenna elements and interference sources, the clutter Doppler frequency is not stationary. Recent works have demonstrated the benefits of combining frequency diversity and space-time adaptive processing (STAP) for distributed aperture radars. In this study a new waveform diversity system model is developed. Using orthogonal signalling, the receivers can treat the incoming signals independently, solving several bistatic problems instead of the initial multistatic problem. The authors also apply adaptive techniques to counteract the range dependency of the clutter Doppler frequency. In particular, the authors apply the joint domain localised algorithm, specifically chosen because of its need for only limited secondary data. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Robust Doppler ambiguity resolution using multiple paired pulse repetition frequencies

    Page(s): 375 - 383
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (698 KB)  

    In the present study, a robust algorithm for Doppler ambiguity resolution is proposed. This new algorithm is based on a recently developed robust phase unwrapping (RPUW) algorithm and the Ferrari-Be-renguer-Alengrin (FBA) method using multiple pulse repetition frequencies (PRF). In the FBA method, the PRFs are grouped into pairs and each paired PRF values are symmetric about 1. Then the Doppler frequency estimation is divided into two steps (folded frequency, i.e. the fractional part and ambiguity order, i.e. the integer part): the folded frequency is estimated by circularly averaging the folded frequency estimates for each pair PRF and the ambiguity order is obtained by searching the finite integers based on a quasi-maximum-likelihood criterion using the estimated folded frequency. By observing that the folded frequency estimates for each pair PRF may have errors because of the finite FFT implementations, noise and interference, the circular mean of the erroneous folded frequency estimates may be erroneous too, which may lead to an erroneous ambiguity order estimate, that is, a large error. In this study, the authors replace the integer ambiguity order searching by a recently developed RPUW algorithm that is robust to the frequency estimates from the FFT implementations. The simulation results of this study show that the newly proposed algorithm significantly outperforms the FBA method and is also better than the RPUW algorithm. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Scatterers characterisation in radar imaging using joint time-frequency analysis and polarimetric coherent decompositions

    Page(s): 384 - 402
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1345 KB)  

    Classical radar imaging generally considers targets as set of isotropic independent sources with a constant response in the measured frequency band. Nevertheless, new radar capabilities, in terms of signal bandwidth and angular excursion, may challenge this bright point model. Studies based on multidimensional time-frequency (TF) analysis, describing the angular and frequency behaviour of a scene-s reflectivity, showed that some scatterers may have anisotropic and dispersive responses. Polarisation diversity is an interesting additional source of information in radar imaging, and provides indicators closely linked to some geometric and electromagnetic properties of the observed objects. In this study, a fully polarimetric TF analysis is proposed for radar imaging (SAR, ISAR) that characterises the anisotropic and dispersive behaviour of the polarimetric response of deterministic targets. This method is based on the hyper-image concept, which describes the response of scatterers as a function of the observation angle, the emitted frequency and polarimetric canonical behaviours. Polarimetric hyper-images point out that non-stationary behaviours can be related to physical properties of the target (geometrical shape, relative orientation) and allow a better understanding of the scattering mechanisms. This polarimetric hyper-image representation is then used to detect non-stationary scatterers and to classify their behaviour. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Passive bistatic noise radar using DVB-T signals

    Page(s): 403 - 411
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (495 KB)  

    This study presents a new approach to passively detect targets using noise-like emitters of opportunity. This method combines the Wiener filtering to achieve clutter rejection and a proposed adaptation to noise-like signals of the amplitude and phase estimation (APES) method. This theoretical approach is confirmed by the detection of a helicopter by a bistatic radar using a digital video broadcasting terrestrial (DVB-T) transmitter. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Measurement and comparative analysis of clutter for GSM and UMTS passive radars

    Page(s): 412 - 423
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1030 KB)  

    Passive radars have been known to the scientific community since their first application as a system to detect bombers by means of shortwaves radiated by radio broadcasting towers in 1935, although they lately raised a renewed interest among researchers for some specific features that make them more appealing than classic active radar systems. In fact, having the transmitter and receiver located at two different positions, and the adoption of signals carrying other kinds of information such as GSM (either classical or the 1800/1900 MHz DCS version) or UMTS waveforms, makes passive radar virtually undetectable and economically advantageous. A measurement system used to characterise the clutter from a GSM/DCS and UMTS-based passive radar is presented. The main objective is to study the statistical properties of the clutter signals, find theoretical models fitting the measured clutter data and analyse the differences between the modulated carriers of the two different standards. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Editorial Special Section on Synthetic Aperture Radar from EuSAR 2008, Friedrichshafen, Germany

    Page(s): 424 - 425
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (77 KB)  

    It is a pleasure to introduce this Special Section of IET Radar, Sonar & Navigation, dedicated to the 2008 European Conference on Synthetic Aperture Radar. EuSAR is the international conference devoted to the technology and techniques of Synthetic Aperture Radar (SAR). The conference is organised biennially and was first established in 1996. Since its inception, worldwide interest in EuSAR has steadily increased. While the first EuSAR featured two parallel sessions, the forthcoming conference (EuSAR 2010 in Aachen, Germany) will be partitioned into five parallel sessions. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Bistatic SAR experiment with the Ingara imaging radar

    Page(s): 426 - 437
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1409 KB)  

    Synthetic aperture radar (SAR) operation in a bistatic configuration not only offers various advantages over its now well-established monostatic counterpart but also poses various challenges. As part of a research programme into the potential benefits and challenges of bistatic SAR, the Ingara fully polarimetric X-band airborne imaging radar system, developed and operated by the Australian Defence Science and Technology Organisation, was upgraded to conduct experimental SAR data collections in a bistatic geometry. Initial trials of the new bistatic SAR system were conducted between December 2007 and April 2008: these involved operation of the existing airborne radar in a fine-resolution (600 MHz bandwidth) circular spotlight-SAR mode, in conjunction with a newly developed fully polarimetric stationary ground-based bistatic receiver. These experimental trials produced a set of fully polarimetric simultaneously collected monostatic and bistatic SAR data, collected over a wide range of bistatic angles. Results from a preliminary analysis of the data have been encouraging: focussed fine-resolution imagery has been obtained, indicating the successful maintenance of synchronisation and phase stability between the independent airborne and ground-based systems. Furthermore, interferometric coherence has been demonstrated between single-pass simultaneously collected monostatic and bistatic images from the airborne and ground-based receivers, and between repeat-pass bistatic images from the ground-based receiver collected some 100 min apart. This study gives an overview of the Ingara bistatic SAR system, discusses the experiments and data processing and presents initial experimental results. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Signal-to-clutter ratio enhancement in bistatic very high frequency (VHF)-band SAR images of truck vehicles in forested and urban terrain

    Page(s): 438 - 448
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1115 KB)  

    Multiple scattering is often a dominating scattering mechanism in VHF-band SAR, in particular in scenes including forested and urban terrain. Most important in this context is multiple scattering generated by double- or triple-bounce scattering from structures with orthogonal corners which often dominate for monostatic SAR geometries. Examples include double-bounce scattering from vertical tree stems or building walls on horizontal ground. In such situations, bistatic SAR may offer a significant advantage compared to monostatic SAR by choosing a suitable bistatic imaging geometry. We give experimental results which show increased signal-to-clutter ratio in bistatic VHF-based SAR (28-73 MHz). Results show that the signal-to-clutter ratio of a vehicle truck in a background of forest and urban clutter increases by up to 10 dB when the broadside bistatic elevation angle increases from 4 to 20??. The results indicate that significant improvement in detection performance can be expected for vehicle-sized objects in forest and urban terrain by using bistatic geometries in VHF-band SAR. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Compact polarimetric SAR interferometry

    Page(s): 449 - 456
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1183 KB)  

    The authors discuss the role and performance of compact polarimetry in SAR interferometry. The considered SAR architecture transmits either a linearly polarised wave oriented at 45?? or a circularly polarised one, and receives at horizontal and vertical polarisation. Two polarimetric acquisitions are combined in an interferometric image, characterised by a polarimetric and interferometric (POLINSAR) covariance matrix. The expression of the covariance matrix for compact polarimetry is derived and the relationship between compact and full polarimetric covariance matrices is discussed. On the basis of symmetry properties of geophysical media, the authors propose a reconstruction algorithm of the full polarimetric information from a compact polarimetric dataset. The algorithm allows the assessment of compact POLINSAR and the comparison between the two compact configurations. The authors consider forested areas and compare the interferometric degree of coherence measured at different polarisations by compact polarimetry and full polarimetry. The study shows that the degree of coherence from a compact polarimetric architecture carries enough information for POLINSAR applications, such as forest parameters retrieval, if the symmetry properties are satisfied. Airborne data acquired by the DLR E-SAR sensor over the Traunstein forest are used to illustrate the results. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Interferometric focusing for the imaging of humans

    Page(s): 457 - 463
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (371 KB)  

    Different recent approaches have demonstrated the feasibility of applying millimetre-waves (MMW) for the imaging of objects at a person's body. The utilisation of MMW allows for the detection of both metallic and non-metallic objects. In order to reduce costs a low number of transmit-receive modules should be used. Furthermore, the person should also be illuminated from different angles in order to avoid shadowing effects as good as possible. A way to fulfil these two conditions is to place one sensor above and another one below the person and either rotate the person standing on a turntable (inverse synthetic aperture radar, ISAR) or move the sensors on a circular path around the person (synthetic aperture radar, SAR). The goal of the reconstruction is to obtain information about the shape of possible threats and their positions in all three dimensions. During processing as a first step, the reconstruction is done along range and azimuth, which span the principal surface given by the suggested sensor configuration. Afterwards, the third spatial dimension can be determined by combined evaluation of the resolution capabilities of the curved synthetic aperture and the interferometric phase of two coherent receiving channels of one sensor. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Interferometric methods for three-dimensional target reconstruction with multipass circular SAR

    Page(s): 464 - 473
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (784 KB)  

    The authors consider three-dimensional (3-D) target construction from SAR data collected on multiple complete circular apertures at different elevation angles. The 3-D resolution of circular SAR systems is constrained by two factors: the sparse sampling in elevation and the limited azimuthal persistence of the reflectors in the scene. Three-dimensional target reconstruction with multipass circular SAR data is further complicated by non-uniform elevation spacing in real flight paths and non-constant elevation angle throughout the circular passes. The authors first study parametric spectral estimation methods that extend standard IFSAR method of height estimation to apertures at more than two elevation angles. Next, they show that linear interpolation of the phase history data leads to unsatisfactory performance in 3-D reconstruction from non-uniformly sampled elevation passes. The authors then present a new sparsity regularised interpolation algorithm to preprocess non-uniform elevation samples to create a virtual uniformly spaced array. The authors illustrate the performance of the proposed method using data from EM simulations and data collected from a wideband X-band airborne sensor. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Acceleration-independent along-track velocity estimation of moving targets

    Page(s): 474 - 487
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1078 KB)  

    In the study a new method for along-track velocity estimation of moving targets is presented. This method exploits the along-track interferometric phase ramp of a range-compressed moving target signal between two or more receiving channels. The slope of this phase ramp is mainly influenced by the along-track velocity but not by accelerations. Hence, acceleration-independent along-track velocity estimation is feasible. A verification of the proposed method is performed by using both simulations and real two- and four-channel X-band data acquired with DLR's E-SAR and F-SAR system. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • ESA'S POLarimetric Airborne Radar Ice Sounder (POLARIS): design and first results

    Page(s): 488 - 496
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (699 KB)  

    The Technical University of Denmark has developed and tested a P-band ice sounding radar for European Space Agency (ESA). With the recent by the International Telecommunication Union (ITU) allocation of a radar band at 435 MHz, increased interest in space-based sounding of the Earth s ice caps has been encountered. ESA s POLarimetric Airborne Radar Ice Sounder (POLARIS) is intended to provide a better understanding of P-band scattering and propagation through ice sheets and to verify novel surface clutter suppression techniques in preparation for a potential space-based ice sounding mission. POLARIS is a nadir-looking, fully polarimetric radar featuring aperture synthesis, a multi-aperture antenna for surface clutter suppression and a large dynamic range based on a shallow/deep sounding approach. The system is installed in a De Haviland DHC-6 Twin Otter aircraft, and in May 2008, a proof-of-concept campaign was conducted in Greenland. This study outlines the design and implementation of the system, and based on first results it is concluded that in the central dry snow zone of Greenland, POLARIS can resolve shallow and deep internal ice layers, penetrate the thickest ice encountered and detect the bedrock. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.

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.

Full Aims & Scope

Meet Our Editors

Publisher
IET Research Journals
iet_rsn@theiet.org