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Randomisation of element positions in a sparsely populated, non-uniform antenna array is a well-known approach in communication systems for controlling grating lobes and allowing improved spatial resolution for a given number of antenna elements. MIMO array techniques have been applied more recently to radar systems with a view to improving the versatility and performance, particularly angular resolution, of a system with a given number of elements. A sparsely populated, non-uniform MIMO array would therefore seem a logical and attractive combination, though its performance is rather more difficult to predict and less easy to control because of geometrical constraints. This study sets out to examine the spatial sidelobe performance and potential for grating lobe control of a sparsely populated MIMO radar array architecture using antenna position randomisation to suppress grating lobes. [ABSTRACT FROM AUTHOR]

To achieve high-resolution two dimension images, synthetic aperture radar (SAR) with ultra wide-band faces considerably technical challenges such as long data collection time, huge amount of data storage and high hardware complexity. In these years, several imaging modalities based on compressive sensing (CS) have been proposed which can provide high-resolution images using significantly reduced number of samples. However, the CS-based methods are sensitive to noise and clutter. In this study, a new imaging modality based on Bayesian compressive sensing (BCS) is proposed along with a novel compressed sampling scheme. Clutter, which the previous CS-based methods not considered, is also included in this study. This new imaging scheme requires minor change to traditional system and allows both range and azimuth compressed sampling. Also, the Bayesian formalism accounts for additive noise encountered in the compressed measurement process. Experiments are carried out with noisy and cluttered imaging scenes to verify the new imaging scheme. The results indicate that the Bayesian formalism can provide a sharp and sparse image absence of side-lobes, which is the common problem in conventional imaging methods and has fewer artifacts compared with the previous version of CS-based methods. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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–Bérenguer–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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This study introduces a novel aspect and polarisation invariant radar target classification method based on the use of multiple signal classification (MUSIC) algorithm for feature extraction. In the suggested method, for each candidate target at each designated reference aspect, feature matrices called ‘MUSIC spectrum matrices (MSMs)’ are constructed using the target's scattered data at different late-time intervals. An individual MSM corresponds to a map of a target's natural resonance-related power distribution over the complex frequency plane under the chosen aspect angle/late-time interval conditions. The collection of these feature matrices is used first to determine the best late-time interval for optimal feature extraction. Then, the MSM of a target, which are computed over the optimal time interval at all reference aspects, are superposed to obtain the ‘fused MUSIC spectrum matrix (FMSM)’. The FMSM of a target is its main classifier feature in the proposed method as the aspect dependency of an FMSM is highly reduced because of its multi-aspect construction process. The suggested method is demonstrated for both simple and complex target geometries such as conducting spheres, dielectric spheres and small-scale aircraft targets with high accuracy rates even for low SNR values using feature fusion at only a few different reference aspects. [ABSTRACT FROM AUTHOR]

Ground moving target indication (GMTI) is one of the most important applications of the bistatic synthetic aperture radar (SAR) system as well as the monostatic system. An algorithm for moving target detection and location is presented with an azimuth-invariant bistatic multichannel SAR, which consists of one transmitter (channel) and multireceivers (multichannel). The algorithm is based on the discussion of the particularities of the bistatic SAR configuration including coherence improvement and clutter characteristics. Then, the corresponding compensating methods including two-dimensional range-azimuth prefiltering and bistatic differential range correction are proposed to solve these particularities. It is shown that using the compensating methods, the stationary clutter can be suppressed and the moving parameters of ground targets can be estimated accurately. Finally, simulation results demonstrate the effectiveness of the proposed algorithm. [ABSTRACT FROM AUTHOR]

Radar signature produced by micro-motion structures contains movement and structure information which is useful for radar target recognition. For stepped frequency (SF) radar, the Doppler modulation is coupled with the stepped carrier frequency. It shifts and smears the high-resolution range profile and makes it difficult to analyse and extract the micro-motion information from the range profile directly. The authors propose to comprehend the SF radar as a special pulse Doppler radar, and the range profile as a Doppler profile for the convenience of motion analysis. The signature of moving targets for SF radar is analysed from this point of view and the equivalent instantaneous Doppler frequency (EIDF) is introduced. Then, a typical micro-motion, rotation, is taken as an example. The sinusoidal vibration of the peaks in the range profile sequence is explained in detail, especially the relationship between the sinusoid parameters and the rotation parameters. An approach to extract the rotation parameters from the range profile or EIDF spectrum sequence is proposed based on the Hough transform. Simulated and experimental results validate the theoretical analysis and the feature extraction method. [ABSTRACT FROM AUTHOR]

The problem of adaptive target detection for airborne multi-input multi-output (MIMO) radars with space–time receivers in the presence of Gaussian interference (including clutter and noise) is studied. Previous work has assumed the interference covariance matrix to be known. The case with unknown covariance matrix is investigated here. By exploiting the low rank property of clutter subspace, generalised likelihood ratio test detector and adaptive matched filter detector with diagonal loading are suggested to improve the detection performance of MIMO radars in limited secondary data case. The closed-form detection probabilities and false alarm probabilities of the two proposed detectors are derived and numerically evaluated. Theoretical analysis and numerical results show the advantages of the proposed detectors. [ABSTRACT FROM AUTHOR]

The clutter characteristics of bistatic airborne radar are more complex than those of monostatic airborne radar. The clutter spectra not only vary severely with range, but also vary with bistatic configuration. The problem of range dependence is more serious in monostatic airborne radar. In this paper, the geometry of arbitrary bistatic airborne radar configuration is firstly analysed, and a formula for Doppler frequency calculation with the variables of azimuth angle and bistatic range is deduced, which is an efficient tool for bistatic clutter analysis. Because of the severe clutter range dependence, the processing of compensation is indispensable in space time adaptive processing (STAP). However, when range ambiguity occurs, the compensation is difficult to be applied to each clutter range cell. To solve this problem, a range ambiguity resolving approach is further proposed by utilising azimuth elements in phased array. Because this approach will result in spatial degrees of freedom (DOF) loss, the overlapped subarray processing is introduced in order obtain enough spatial DOF for STAP. By doing so, the compensation for mitigating range dependence can be applied effectively to bistatic clutter. [ABSTRACT FROM AUTHOR]

In modern radar systems, using stepped-frequency pulse train is an effective approach to achieve high-range resolution (HRR) with narrow instantaneous bandwidth and low system complexity. However, if the parameters of stepped-frequency (SF) radar (such as single pulse bandwidth, frequency step size and sampling instant) are not prudently designed, ‘ghost image’ phenomenon (also called range ambiguity in some literature) will corrupt the synthetic HRR profiles. The relationship between parameters of the SF radar and the ghost images is provided analytically. A new synthetic range profiling algorithm is developed to generate HRR profiles without ghost images by using the least-squares (LS) estimation. For targets with negligible radial velocities, the new LS profiling algorithm can eliminate the ghost images successfully, and introduces less signal-to-noise ratio loss. With this algorithm, the restriction on the frequency step size is less rigid than the traditional unambiguous criterion. Consequently, a higher range resolution could be obtained. Simulations and field experimental results are also presented. [ABSTRACT FROM AUTHOR]

Results from an experiment that applied one class of multiple-input multiple-output (MIMO) waveform techniques to over-the-horizon radar (OTHR) are reported. The experiment objective was to demonstrate that adaptive transmitter beamforming could be used in an appropriately design radar to reject spatially discrete Doppler-spread clutter. In the particular MIMO radar architecture that the authors call non-causal transmit beamforming, conventional or adaptive transmitter beamforming occurs following waveform transmission, propagation, scatter from targets and clutter sources, return propagation and finally signal reception. In the case reported herein spatially discrete clutter was successfully rejected to the noise floor of the radar return with rejection in excess of 35 dB achieved using common adaptive algorithms and straightforward training data selection. As part of the rejection algorithm the transmitted waveform direction-of-departure (DOD) from the transmitter array to the target was estimated and used as the preserved steer direction in the adaptive beamformer. The DOD estimates agree well with the geometrically determined true values. The demonstration of non-causal transmit beamforming suggests that it will be possible to create multiple simultaneous adaptive range-dependent transmitter beams with an appropriately designed OTHR. This has several applications including for the mitigation of Doppler-spread clutter. [ABSTRACT FROM AUTHOR]

Multiple-input, multiple-output (MIMO) radars enhance performance by transmitting and receiving coded waveforms from multiple locations. This paper describes MIMO techniques that can be used to improve radar performance, especially in airborne Ground Moving Target Indicator (GMTI) applications. The authors begin by showing how MIMO techniques can lower airborne radar clutter to noise ratios (CNRs). This results in smaller losses when observing stationary or low-velocity targets. Next, the authors consider the implementation of MIMO radar modes using electronically scanned arrays (ESAs). Specifically, the authors show how MIMO techniques, applied to subarray-based ESAs, can cause high grating lobes and/or reduced search rates. To address this problem, the authors describe new space–time waveform coding techniques that can be used to improve performance. Two space–time waveform encoding approaches are proposed: (i) an overlapped virtual transmit subarray approach, and (ii) a beamspace MIMO approach. A third approach, involving conventional MIMO waveforms and irregular subarrays, is also briefly considered. [ABSTRACT FROM AUTHOR]

This study presents a comparative study of coherent and non-coherent target localisation techniques for multiple-input multiple-output (MIMO) radar systems with widely distributed elements. Performance is evaluated based on closed-form solutions developed for the best linear unbiased estimator (BLUE) for each of the localisation methods. These estimators afford insights into the relation between radar locations, target location and localisation accuracy. In particular, the means squared error of the BLUE is factored into a term dependent on signal and processing characteristics and a term dependent on sensor locations. The latter is referred to as geometric dilution of precision (GDOP). The best achievable accuracy for the coherent case is obtained, and a comparative study with the non-coherent case is presented. MIMO radar systems with coherent processing are shown to benefit from a gain because of coherent processing among sensors. This gain is referred to as coherent localisation gain, and it is proportional to the ratio of the signal carrier frequency to the effective bandwidth (a large ratio for typical signals). The footprint of multiple transmit/receive sensors results in a gain, referred to as MIMO gain, for both processing techniques. The MIMO gain is proportional to the product of the number of transmitting and receiving sensors. Analysis of the MIMO gain through the use of GDOP contour maps demonstrate the achievable accuracy at various target locations for a given layout of sensors. [ABSTRACT FROM AUTHOR]

The authors present illumination waveforms matched to stochastic targets in the presence of signal-dependent interference. The waveforms are formed by SNR and mutual information (MI) optimisation. We also use these waveforms in cognitive radar (CR) target identification application. In this application, the radar system attempts to identify a deterministic or random target using multiple transmissions. These transmissions are adaptively modified in response to previously received echoes. In addition, the authors present a new multi-band application of the CR platform. [ABSTRACT FROM AUTHOR]

The authors consider the problem of knowledge-aided covariance matrix estimation and its application to adaptive radar detection. The authors assume that an a priori (knowledge-based) estimate of the disturbance covariance M, derived from a physical scattering model of the terrain and/or of the environment, is available. Hence, starting from a set of secondary data, the authors evaluate the maximum likelihood (ML) estimate of M assuming that it lies in a suitable neighbourhood of the a priori estimate and formulate this ML estimation in terms of a convex optimisation problem which falls within the class of MAXDET problems. Both the cases of unstructured and structured disturbance covariance are considered. At the analysis stage, the authors assess the performance of the new knowledge-aided covariance estimators both in terms of estimation error and detection probability achievable by a class of adaptive detectors. The results highlight that, if the a priori knowledge is reliable, satisfactory levels of performance can be achieved with considerably less training data than those exploited by conventional algorithms. [ABSTRACT FROM AUTHOR]

The authors consider space–time adaptive processing (STAP) when the radar returns are recorded by a conformal antenna array (CAA). The statistics of the secondary data snapshots used to estimate the optimum weight vector are not identically distributed with respect to range, thus preventing the customary STAP processor from achieving its optimum performance. The compensation of the range dependence of the secondary data requires precise knowledge of the array response for any direction of arrival (DOA), and, thus, of the spatial steering vectors (SVs). The authors propose a novel registration-based range-dependence compensation algorithm that gives an accurate estimate of the interference-plus-noise covariance matrix under the hypotheses that calibrated spatial SVs are available only for a small set of DOAs, and that the errors in the model giving the true spatial SV for each DOA are DOA dependent. The performance in terms of signal-to-interference-plus-noise ratio loss is promising. [ABSTRACT FROM AUTHOR]

This paper deals with the problem of non-cooperative target recognition. Specifically, the aim is the automatic recognition of ship targets from inverse synthetic aperture radar (ISAR) images. For this purpose a new two-step multi-feature based technique is proposed; this technique uses a number of features extracted from the ship radar image and matches these features with those extracted from the images obtained by properly projecting the target models of the classification library. Both cases of a priori known or unknown ship aspect angles are considered: the knowledge of the ship aspect (as available from tracking data) allows the selection of the candidate models on the basis of the matching between the ship and the model length, thus resulting in a performance improvement. Moreover, both single- and multi-frame-based processing techniques are proposed in order to assess the performance improvement achievable when an increasing number of ISAR images are involved in the decision; the fusion strategy adopted for the exploitation of the information from the multiple images is also described. The performance of the overall proposed technique is deeply investigated against simulated data. Results of its application to a set of live ISAR images of a ship target are also provided showing the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

The authors address the problem of multipath cancellation in the reference signal used in passive bistatic radar (PBR), which exploits an existing transmitter as emitter of opportunity. The presence of multipath echoes in the reference signal is demonstrated to strongly affect the detection performance of passive radar. Based on the well-known constant modulus algorithm (CMA) approach in the time-domain, new multi-dimensional techniques are considered for the adaptive equalisation of the reference signal based on an array of antennas and multiple receiving channels. The effectiveness of these techniques for PBR purposes is demonstrated with reference to typical simulated scenarios. The considered strategies, addressed as space-CMA and space–time-CMA, are shown to be able to recover the performance loss because of the multipath contribution in the reference signal so that they appear as very appealing solutions for PBR equipped with an array of antennas and multiple receiving channels. [ABSTRACT FROM AUTHOR]

Limitations on accuracy of Doppler estimation in continuous-wave noise radar with correlation processing are studied. Second-order properties of output of the correlation receiver are evaluated and an approximate Cramér–Rao bound on errors of Doppler measurement is derived. The accuracy of Doppler measurements is found to be affected by the following factors: power spectral density of noise signal, frequency response of the low-pass filter in correlator, observation time, velocity of the target and signal to noise ratio. It is shown that the random nature of the transmitted signal induces additional fluctuations at the output of correlator which limit the accuracy even in the infinite signal to noise case. Qualitative extension of the results to a case covering multiple targets and clutter is made. It is argued that the performance will decrease and that increasing transmitted power may not provide significant improvement when clutter is present. [ABSTRACT FROM AUTHOR]

Range sidelobes, a major shortcoming of radar pulse compression, are often reduced through the use of mismatched filters. The authors propose to blank the remaining sidelobes by using two or more mismatched filters, whose sidelobes are designed to peak at different delays. The authors show how to design such filters and present promising simulation results with two or more mismatched filters. [ABSTRACT FROM AUTHOR]

A multiple-input multiple-output (MIMO) configuration has been studied for communication applications, offering a lot of advantages to mitigate propagation effects because of multipath and fading environments. More recently, MIMO techniques in radar have been proposed. MIMO is discussed in the context of high-frequency surface waves radar (HFSWR). After a short introduction to the MIMO radar technique (a technique which is not new; the RIAS developed by ONERA was probably the first MIMO radar), explores two different applications are explored. The first application aims at improving the resolution and accuracy of a coastal radar, proposed here in a bistatic configuration. Such a radar operates with a wide sparse frequency band and with an equivalent wide aperture, taking advantage of the MIMO configuration. Simulation over a congested area of targets demonstrates the benefit of MIMO over the conventional HFSWR radar, especially in terms of separation of targets. The second application consists in a more practical ship-borne HFWSR configuration compatible with space time adaptive processing (STAP) to improve the detection of slow targets. In this case, a limited number of receiving channels is considered whereas STAP uses the degrees of freedom offered by the transmitting array. The MIMO-STAP is compared with a conventional STAP, showing that theoretical performances should not be affected by the MIMO configuration even if the signals are no longer perfectly orthogonal, because of Doppler shift, once scattered by moving targets. [ABSTRACT FROM AUTHOR]

Automatic target recognition using high-range resolution radars is a difficult task. Variations in the distance to the target cause circular shifts of the received signal, and most of the classification algorithms are very sensitive to shifts over the input signal. This fact makes the alignment of each signal prior to any classification stage very important. Here the alignment of noisy signals using the zero phase method is studied. In order to evaluate the performance of the alignment method, a theoretical analysis of the sensitivity to noise of this alignment method is carried out. As a result, an analytical expression that predicts the error of the alignment method is obtained. The validity of this expression is also confirmed by experimental results. A database of high-range resolution radar profiles containing patterns belonging to six different targets has been used, and a comparative study of the sensitivity to noise estimated using the profiles of the database and predicted by the analytical expression is carried out. The results demonstrate that the proposed analytical expression is useful to analyse the sensitivity to noise of the zero-phase alignment method for medium and high signal-to-noise ratio values. [ABSTRACT FROM AUTHOR]

The problem of detecting slow-moving targets using a space-time adaptive processing (STAP) radar is addressed. The determination of the optimum interference-rejection weights at each range is based on snapshots at neighbouring ranges. However, in virtually all bistatic configurations or/and when using conformal antenna arrays (CAA), snapshot statistics are range dependent, which results in poor detection performance. To address this issue, a foundation for range-dependence compensation in STAP in the case of Gaussian interference and noise is proposed. The realistic case where received snapshots are the only source of information for mitigating the range dependence is considered. To illustrate the usefulness of the proposed foundation, this foundation is used to design a method to adaptively compensate for range dependence in a challenging situation, that is, for a radar using a CAA and operating in a bistatic configuration. [ABSTRACT FROM AUTHOR]

Inverse synthetic aperture radar (ISAR) imaging of air, space or ship targets with complex motion has attracted the attention of many researchers in the past decade. Complex motion of targets induce cross-range scatterer-variant quadratic phase terms, which will degrade the cross-range resolution and affect focusing quality. A new algorithm is proposed for the ISAR imaging of complex moving targets. First, conventional range alignment, phase compensation and range compression are performed over the raw phase history data such that each range bin can be modelled as the sum of several linear frequency modulation or chirp signals. Secondly, a modified-Wigner–Ville distribution (referred to as M-WVD) approach is proposed, which is based on a scale transform in the time-frequency distribution plane and can effectively suppress the troublesome cross-term interference associated with WVD via coherent integration. Finally, the azimuth ISAR image can be obtained via a simple maximisation projection from the two-dimensional accumulated plot to the azimuth dimension. Compared with existing WVD-based ISAR imaging algorithms, the proposed method has the following features: better cross-term interference reduction achieved at no resolution loss, computationally more efficient with no expensive two-dimensional parameter search, and higher signal processing gain because of coherent integration during the whole imaging time. Both numerical and experimental results are provided to demonstrate the performance of the proposed method. [ABSTRACT FROM AUTHOR]

A practical passive bistatic radar that is based on target illuminations by digital audio broadcasts is described. As with all such radars, direct signal interference (DSI) is identified as a major limitation, the effect being exacerbated by the multiplicity of illuminators. In addition, such multiplicity can also make the extraction of the original transmitted signal difficult. DSI is reduced by a combination of analogue and digital null formation and isolation by use of cross polarisation. Fast techniques are developed for signal extraction and digital null formation, allowing these operations to be achieved in real time. Both the hardware and algorithms of the system are described and representative radar observations are included to show the systems effectiveness. [ABSTRACT FROM AUTHOR]

The problem of automatically extracting building dimensions from synthetic aperture radar (SAR) image sequences of urban scenes is considered. An algorithm based on the delineation of shadows using active contours constrained by a simple wire-frame building model has been developed and demonstrated using SAR imagery of a village on Salisbury plain. The core of the algorithm is a novel technique for target delineation involving multiple active contours evolving simultaneously. In particular, a technique referred to as multiple hypothesis delineation, in which contours can be in several states simultaneously, is developed and shown to lead to considerable improvement in convergence time and delineation accuracy when used to delineate multiple targets in close proximity. The technique is applied to the automatic estimation of building dimensions by delineation of shadows in a sequence of SAR images of an urban scene. The estimation of building dimensions is automatic; user interaction is limited identifying a building of interest and a region of background clutter close to the building. Results are presented for six different buildings, in each case two SAR images were used in the estimation process separated in illumination angle by either 28° or 90°. The estimates of building dimensions are compared with the actual building dimensions obtained from architectural drawings. The algorithm was found to perform robustly and provide reasonably accurate estimates of the building dimensions, typically within ∼10% of the true values. [ABSTRACT FROM AUTHOR]

The superiority of multiple-input multiple-output (MIMO) radars over conventional phased-array radars has been recently shown in many aspects. The MIMO radars have better detection performance and can extract target information more precisely than phased-array radars. The problem of adaptive target detection using temporal coherent pulse train in the presence of nonhomogeneous clutter (different clutter statistics in receivers) is considered for MIMO radars. This problem has been formulated as a hypothesis test. For clutter with unknown statistics three adaptive decision rules have been developed using the generalised likelihood ratio test. The results show the superiority of the MIMO radars with temporal coherent processing over conventional phased arrays in the presence of clutter. [ABSTRACT FROM AUTHOR]

Binary integrators are an important part of the receiver in many operating radar systems. The optimisation of a binary integrator is not a simple task, because it requires the solution of a (k×n)-dimensional nonlinear optimisation problem, where n is the number of integrated bits (or the number of sensors in a distributed radar or sensor network) and k is the number of the design parameters of the single-pulse detector. An algorithm that converts the multi-dimensional optimisation problem into a one-dimensional problem, so reducing considerably the computational complexity, is developed. This reduction in computational complexity makes the real-time optimisation possible and practical, so it is very helpful for mobile sites in which the optimisation should be performed continually. The proposed algorithm can be applied when either the ‘AND’ or the ‘OR’ integration rule is adopted. The results are illustrated by means of two study cases. In the first case, the binary integrator of a constant false alarm rate radar detector is optimised; in the second one a decentralised detection system composed by n similar sensors is considered and the decision rules are jointly optimised according to the Neyman–Pearson criterion. [ABSTRACT FROM AUTHOR]

The extension of the dynamic range performance of existing radar systems is integral to the requirement for current sensors to see deeper into clutter, that is, to detect weak signals (e.g. small targets) in the presence of strong interference (e.g. urban clutter signals). The rationale behind this requirement is that this additional capability greatly enhances the utility of military and commercial systems. Two approaches to improving the dynamic range of modern radar and surveillance receivers are described: (1) linearisation of intermodulation distortion (IMD) using digital post-distortion algorithms and (2) linearisation of IMD using frequency retranslation mixer (FRM). The experimental results presented illustrate that the digital post-distortion and FRM approaches are effective in providing IMD improvements for the hardware and test scenarios measured. The improvements measured ranged from 15 to 35 dB for narrowband signals to 2–6 dB for frequency-modulated continuous wave (FMCW) wideband signals. The digital post-distortion approach provided the greatest performance improvement when the input signals were between the analogue-to-digital converter full range and 20 dB below that level. The improvements measured for the FRM linearisation approach ranged from 20 to 25 dB for the narrowband two-tone tests and 16–18 dB for the wideband FMCW signal chirps. [ABSTRACT FROM AUTHOR]

A synthetic aperture radar system can be made compatible with other interleaved modes if the impact of the interruptions in operation necessary to accommodate these can be ameliorated. The ways in which this might be done are discussed. Effects of regular and random interruptions are characterised by simulation and analysis. Two methods of image enhancement, based on interpolation and apodisation, are then discussed; the latter appears to hold more promise of practical usefulness. [ABSTRACT FROM AUTHOR]

An accurate approach to power budget analysis for forward scattering radar with application to the detection of ground targets is presented. A modification of the range equation is used, and the results of experimental testing for its confirmation are given. [ABSTRACT FROM AUTHOR]

High-resolution radar sea clutter exhibits long-term temporal and spatial correlation features consistent with the sea surface wave structure. Data are presented showing that there is a transient coherence in the long-term fluctuations of the clutter, which locally appears to show the single periodic fluctuation of a dominant wave, but when averaged over a large area is seen to contain a wide band of fluctuation frequencies. This apparently non-stationary behaviour makes it difficult to predict the local sea clutter level for constant false alarm rate (CFAR) thresholding using conventional techniques. A new method of scan-to-scan CFAR processing is therefore proposed, which takes account of this behaviour. The scheme is analysed and its performance characterised. [ABSTRACT FROM AUTHOR]

Progress in the study of space-surface synthetic aperture radar is presented. Global navigation satellite system is considered as the transmitter of opportunity. It highlights the various important issues to successfully obtain an image. The experimental testing of the imaging algorithm is presented and verified using a GLONASS satellite signal. [ABSTRACT FROM AUTHOR]

The performance of netted radar is evaluated in terms of a netted version of the radar equation and the ambiguity function. A software simulation has been developed to allow assessment of netted radar sensitivity and ambiguity properties in both two-and three-dimensional space. Simulation results demonstrate that coherent netted radar sensitivity depends not only on the radar parameters, but also on the numbers, locations and specification of transmit and receive nodes. The netted radar ambiguity function is affected by a combination of many factors. In addition to those that determine the form of the monostatic ambiguity function, the locations of transmit and receive nodes as well as the position and velocity of the target all are shown to play an important role in evaluating system performance. As a result of these dependencies, it is shown that there is severe degradation of range and Doppler resolution when a target crosses sufficiently close to a transmit–receive baseline. [ABSTRACT FROM AUTHOR]

A novel technique to obtain position, velocity and radar biases estimates of a ship is described by matching ship-borne radar images to geo-referenced satellite images. The matching is performed through the minimisation of the averaged partial Hausdorff distances between data points in each image. The minimisation rapidly yields robust geographical latitude and longitude position measurements, as well as ship heading and radar biases. The accuracy of the measurements is improved by feeding them into a Kalman filter that also allows estimates of the ship's velocity to be obtained. The method provides an alternative effective position sensor for GPS denied environments, which may also be employed for automatic radar calibration of bearing and range biases or for indoor autonomous mobile robot navigation. [ABSTRACT FROM AUTHOR]