The focus of this study is on the estimation of the kinematic parameters of a moving target via a multiple-input-multiple output (MIMO) forward scatter radar (FSR) system. For this purpose, a crossing time-based estimation technique is proposed that exploits the information on the time instants at which the target crosses the individual baselines of multiple FSR nodes to retrieve the target motion parameters. First the accuracy of such technique is investigated from a theoretical point of view through Monte Carlo simulations and then the effectiveness of the proposed approach is demonstrated by applying it to measured MIMO FSR data. Shown results prove the practical applicability of the proposed technique and demonstrate the potential of MIMO FSR configuration.

The joint exploitation of polarimetric and frequency diversity is considered in this study as a way to improve the target detection capability in a FM radio-based passive radar. The authors resort to a generalised likelihood ratio test approach and derive a fully adaptive multi-frequency polarimetric detector that optimally combines the signals simultaneously transmitted by a given illuminator of opportunity and received at different carrier frequencies by differently polarised surveillance antennas. The application of the proposed detection scheme to recorded live data demonstrates the effectiveness of the multi-frequency polarimetric operation in typical scenarios, besides the expected improvement due to non-coherent integration of target echoes received on multiple channels. In particular, it is shown to provide remarkable target discrimination capability against interfering sources as well as increased robustness with respect to the time-varying characteristics of the exploited signals of opportunity.

This study is concerned with the characterisation of Doppler spectra from high range resolution X-band radar sea clutter observed from an airborne platform over the range of grazing angles, 15° to 45°. It is observed that when looking up or down wind there is a strong correlation between mean Doppler shift and local spectrum intensity. When combined with random fluctuations of spectrum width, these characteristics give the spectra a temporal and spatial variability. This behaviour has previously been observed in low grazing angle data and these results confirm the wider applicability of the models developed using that data. The modelling method is also extended here to capture the bimodal behaviour observed with high intensity returns from breaking waves looking up or down-wind.

This study is concerned with the assessment of models of Doppler spectra, derived from high range resolution X-band radar sea clutter observed from an airborne platform over the range of grazing angles, 15–45°. When looking up or downwind these models represent the strong correlation between mean Doppler shift and local spectrum intensity. When combined with random fluctuations of spectrum width, these characteristics give the spectra a temporal and spatial variability. The models are used to predict clutter spectrum statistics as a function of Doppler frequency and these are compared with statistics derived from the original data. It is also shown how realistic range-varying coherent clutter returns can be simulated using the models.

Radars are developed with the aim to process any type of signals even in the presence of interferences in a hostile context. The authors propose a circuit which can deal with any signal, whatever its frequency, its modulation scheme. This circuit is based on sampled analogue signal processor (SASP) performing a fast Fourier transform (FFT) using voltage samples. The idea is to process any radio frequency signal from 0 to 5 GHz using the FFT to obtain frequency shifting and filtering, presenting a new approach to reduce dramatically power consumption and thus address radar application such as FOPEN. The measurement results presented here on the SASP have been obtained with a 65 nm CMOS technology from STMicroelectronics. Further, the concept of an active interference-cancelling system using the analogue signal processor in a feed-forward loop is presented.

Slow moving ground targets are invisible within synthetic aperture radar (SAR) images since they appear defocused and their backscattered signal completely overlap the focused ground return. In order for this targets to be detected and refocused the availability of some spatial degrees of freedom is required. This allows for space/slow time processing to be applied to mitigate the ground clutter. However, multichannel SAR (M-SAR) systems are very expensive and the requirements in terms of baseline length can be very restrictive. In this study a processing scheme that exploits high PRF single channel SAR system to emulate a multichannel SAR is presented. The signal model for both target and clutter components are presented and the difference with respect to an actual M-SAR are highlighted. The effectiveness of the proposed processing is then demonstrated on simulated a measured dataset.

An algorithm for three-dimensional (3D) target reconstruction is proposed in this study. Such an algorithm is based on the use of 2D inverse synthetic aperture radar (ISAR) imaging and interferometry. The proposed algorithm is able to operate with both bistatic and squinted geometry, thus allowing its applicability to all possible geometrical configurations. A mathematical foundation of the algorithm is provided in this study followed by a validation through the use of both simulated and real data.

This study presents a new asphalt radar, operating in the band from 13 to 17 GHz, intended for mobile road surveying of road pavement surface layers. A wide frequency band is required since new asphalt overlays are very thin in Finland being less than 50 mm in thickness. Therefore, sufficient spatial resolution of the radar system is required so that the subgrade would not affect the measurement result of the surface course. This study presents new results of the measurement campaign carried out on a newly-laid highway lane in Finland during summer 2014. The permittivity values on the trial section of the lane varied between 2.1 and 6.4. Two samples were drilled from the road in order to obtain reference permittivity values, measured in a laboratory using a 7 to 17 GHz scanner producing a 2D image of the permittivity. The permittivity values obtained using the scanner varied between 4.3 and 9.5 and they relate to the structural variation of the permittivity with a 5 mm × 5 mm resolution. The results indicate that permittivity values can be used for monitoring the change in asphalt density condition when it is performed as a follow-up survey.

Runway operation is the limiting factor for the overall throughput of airports. Today the International Civil Aviation Organization (ICAO) imposes wake vortex separation minima between following aircrafts that are based on simple pair-wise rules. However, the lifetime of wake vortices results from a much broader basis of factors, that ranges from a large set of aircraft parameters to meteorological conditions and traffic mix. In particular atmospheric conditions can significantly reduce wake hazard, for instance, in case of strong turbulence or crosswinds. While such situations could allow a reduction of the separation minima, safety reasons and the current technical challenges of detecting and managing such scenarios leads to the strict application of the ICAO standards. With the aid of accurate wind data and precise measurements of wake vortices, more efficient intervals could be set, particularly when weather conditions turn favourable. Depending on traffic intensity, these adjustments could enhance airport capacity, and generate major commercial benefits. This study deals with recent development in the radar technology to attain such goals. It presents (i) the trials of an electronic scanning radar to be used in a future wake turbulence advisory system and (ii) theoretical and numerical analysis of the radar response in clear air and in rainy weather. Part of this work has been achieved with the support of the European ATM research program SESAR.

In this study, the problem of efficient implementation of a coherent integration processor in passive bistatic radars (PBRs) in the presence of range migration is addressed. The authors present a coherent integration architecture for PBR, which consists of a frequency-domain pulse compression module to reduce the overall runtime for the computation of the cross-ambiguity function, and an efficient decimated keystone transform module based on the chirp z-transform to compensate the range migration. The proposed architecture is then implemented in a hybrid central processing unit plus graphic processing unit scheme. Real measurement data are used to verify the superior integration performance and reduced computational complexity achieved by the proposed scheme.

For detection of target submerged in the spread Doppler spectrum of the first-order sea clutter in shipborne high-frequency surface-wave radar (HFSWR), there still remains a challenge. In this study, an improved orthogonal weighting (OW) algorithm is proposed for shipborne HFSWR to suppress sea clutter in both Doppler domain and spatial domain. By combining OW with the method of sea clutter suppression in Doppler domain, the performance of azimuth estimation of OW is thus preserved. Compared with OW and two-dimensional fast Fourier transform plus digital beamforming, this new approach is verified to be more effective by simulations and real data.

Integrity of positioning is one of the key aspects of satellite based augmentation systems. This paper presents a study carried out in north-eastern Poland, a region which is considered as a border of the operation of the European Geostationary Navigation Overlay Service (EGNOS) system. Detailed analyses concerning operational parameters of EGNOS were done during the 12-hour and 24-hour measurement sessions conducted at a fixed point. The study was focused on the role of ionospheric delays in the integrity model according to the Radio Technical Commission for Aeronautics guidelines. In determination of the accuracy and integrity of positioning, two variants of calculations were adopted: one based on a standard interpolation algorithm determining ionospheric delay by the EGNOS system, and the other based on the Klobuchar model. The research found that the first method is characterised by only slightly better accuracy results, while significant differences were obtained by examining the integrity of positioning. For both variants of the calculation design, the values of protection levels determined for the fixed point are much higher than the positioning accuracy, which meets the integrity requirements of the navigation system.

Non-rigid image registration is an important preprocessing step in synthetic aperture radar (SAR) image applications. A crucial problem that involves in it is to reliably establish the correspondences between the feature points extracted from both the reference and sensed image. In this Letter, a non-rigid registration method is proposed to align two SAR images by registering two sets of feature points extracted from the images. In the proposed method, both point-wise background regional similarity and local spatial constraint are utilised to find correct correspondences between two feature point sets. Point-wise background regional similarity is introduced to enhance feature points similarity measurement. Meanwhile, based on the adjacent spatial relationship between feature point and its neighbouring points, a new concept of local spatial constraint is further proposed to robustly characterise the geometric consistency between them, which is designed to reduce the ambiguous matches aroused by speckle noise and feature outliers. By combining these two improvements, the authors generate a new matching cost function and formulate non-rigid image registration as a correspondence optimisation problem, which can be solved by the probabilistic relaxation method. Experimental results on both simulated and real deformed SAR images indicate the robustness and effectiveness of the proposed method.

Multichannel autofocus (MCA) is a subspace-based autofocus method for solving the defocusing problem in synthetic aperture radar. In addition to the one-dimensional (1D) defocusing assumption, MCA assumes that the perfectly focused image has a low-return region, which is naturally guaranteed by the spatially limited nature of the radar antenna footprint. In theory, MCA yields better or even perfect solutions compared to other autofocus methods. However, the authors have discovered that MCA is far more sensitive to violation of the 1D defocusing assumption compared to other methods; in fact, MCA is unsuitable for even fairly small data-collection angles. Fortunately, this problem can be solved if they reverse the order of two steps in the image formation process and apply MCA in a domain where the defocusing effect is one dimensional. The distorted version of the image, obtained by inverse Fourier transforming the polar-grid data without further interpolation, contains regions satisfying a low-return assumption, but the region of low return must be carefully specified for best performance. They present simulation results of the proposed method, reversed-step MCA, for various ranges of look angles and discuss the selection of low-return constraints.

In this study, the authors investigate the effects on the range measurement accuracy of a WiFi-based passive radar when multiple copies of signal, from the same target, are received due to propagation through a rich-scattering environment. These multipath returns from stationary scatters induced range measurement inaccuracies in passive radars including offset of the target from its true range, smearing of the target in range dimension or appearance of ghost targets. Relationship between range measurement inaccuracies due to target multipaths and range resolution of transmission waveform has been studied. A two-step solution, that is, signal separation followed by equalisation, is also proposed to mitigate the effects of multipaths in WiFi-based passive radars.

To overcome the shortcomings of the conventional moving target detection method in single-channel synthetic aperture radar (SAR), this study proposes a novel method for moving target detection in single-channel multi-band SAR. In this method, according to the detectable velocity in different bands, the genetic algorithm is applied to optimise the choice of radar band parameters, for example, wavelength and pulse repetition frequency. With the obtained optimal parameter combinations, the multi-band SAR system could achieve the highest velocity detection rate and the maximal bands utilisation rate. Then, moving target detection, imaging and location could be accomplished with the radon transform and the deramp method. Finally, simulation results are presented to demonstrate the effectiveness and feasibility of the proposed method.

With the advantage that antenna pattern and scanning features can be described conveniently in phased array radar, direction cosine coordinates (COS) is widely used. Unfortunately, measurements reported in the COS are non-linear relative to the target states described in the Cartesian coordinates. In addition, it has been proved by the theory and practice that the tracker can perform better by making full use of the Doppler measurement. This study mainly focuses on dealing with the position and Doppler measurement in the COS. Firstly, a pseudo measurement constructed by the product of range measurement and Doppler measurement is utilized to reduce the high non-linearity between the target state and the Doppler measurement. Then, via taking the fourth-order terms of a Taylor series expansion, the consistent estimation of converted measurements errors is obtained based on current measurements. Finally, in order to process the converted position measurements and pseudo measurement sequentially, Cholesky decomposition is exploited to decorrelate the converted position and pseudo measurement errors. Simulation results illustrate that the filter presents a higher estimation accuracy of target states, whether the target is moving or static. Furthermore, compared with unscented Kalman filter, the calculation load of the proposed filter is reduced significantly.

The detection of partial discharge (PD) sources in electrical equipment is very important for safe and stable operation of power systems as it allows for the timely elimination of insulation faults. Cross, circular and square array sensors are commonly used in the detection. In order to determine which form is the best, this study compares the acoustic performance and positioning accuracy of the different arrays. Firstly, this study does research on the quantitative evaluation of the acoustic performance of the planar ultrasonic array sensors. Sparse signal decomposition theory is then applied to find three different directions of arrival (DOAs) of the signal from the PD source to the array sensor. Next, using two of the DOAs (azimuth and pitch), the location of the PD is determined as the centre of a sphere whose surface is tangential to the three DOAs in three different planes. The positioning accuracy of the sensors is then derived. Finally, simulation results show that the acoustic performance of the circular array is the best. It also produces the most accurate location results. Therefore, a circular array is the optimal form to use for the construction of a planar array sensor.

FM-based passive bistatic radars (PBRs), exploiting a single broadcasted channel, have limited range resolution due to low modulation bandwidth and high dependence on the content broadcasted from an FM station. This may be alleviated by exploiting multiple broadcasted channels from a single transmitter. To reach these goals, the authors formulate the problem of detecting a target in the presence of interference signals, such as receiver noise, direct signal, multipath/clutter echoes, and interfering targets, as a composite hypothesis test. So, they derive a multiband uniformly most powerful invariant test. In the proposed detector, they analytically show how the exploitation of the multiple broadcasted channels can improve the target range resolution. The false alarm rate and detection probability of the proposed detector are also derived in the closed-form expressions. Finally, they provide some simulation examples to validate the authors’ theoretical analysis. Simulation results show that a multiband PBR system offers advantages in terms of coherent combined diversity gain and target range resolution improvement as compared to a single band PBR system.

The subspace-based methods are effectively applied to classify sets of feature vectors by modelling them as subspaces. However, their application to the field of non-cooperative target identification of flying aircraft is barely seen in the literature. In these methods, setting the subspace dimensionality is always an issue. Here, it is demonstrated that a modified mutual subspace method, which uses softweights to set the importance of each subspace basis, is a promising classifier for identifying sets of range profiles coming from real in-flight targets with no need to set the subspace dimensionality in advance. The assembly of a recognition database is also a challenging task. In this study, this database comprises predicted range profiles coming from electromagnetic simulations. Even though the predicted and actual profiles differ, the high recognition rates achieved reveal that the algorithm might be a good candidate for its application in an operational target recognition system.

Pareto plus noise clutter distribution has been introduced recently as a good candidate model for X-band high resolution maritime clutter returns. In this study, the authors derive a non-integer order moments estimator (NIOME) and [zlog(z)] based estimator to find the parameters of this distribution in the case of non-coherent integration of N-pulses. For this, the authors first develop an asymptotic formula of moments with non-integer order which is expressed in terms of the gamma and the generalised hypergeometric functions. Then, the authors derive [zlog(z)] based approach as a function of the log based moments and the generalised hypergeometric function. By accommodating a non-integer moments and moments of orders one and two, the proposed estimators are given so that non-linear estimates of the shape parameter are achieved using numerical computations. Through synthetic and real data, the authors show numerous examples demonstrating the applicability of the estimation procedures as a function of clutter-plus-noise parameters. The obtained results illustrate that the proposed NIOME method is asymptotically efficient especially for multiple looks case and high sample size.

The problem of moving target indicator (MTI) filter design for radar systems with non-uniform (staggered) pulse repetition intervals is examined. The goal is to realise and then utilise a trade-off in the design of MTI filter between the conflicting requirements of high suppression of undesired signal (clutter echo) and minimal suppression of desired signal (target echo). To that aim, three design methodologies, namely, least squares, convex optimisation and min–max error, are studied. The numerical results indicate that the presented designs yield high-performance MTI filters which are easily applicable to a variety of operational scenarios. A ready-to-use source code for the design of suggested filters is also provided.

The growing interest in adopting pulse compression waveforms to non-coherent radar and radar-like systems (e.g. lidar) invites this update and review. The authors present different approaches of designing on–off {1, 0} coded envelopes of transmitted waveforms whose returns can be envelope detected and non-coherently processed. Two approaches are discussed for the aperiodic case: (a) Manchester encoding and (b) mismatched reference. For the periodic case, on–off sequences are described, which produce perfect periodic cross-correlation when cross-correlated with one or more integer number of periods of a two-valued reference sequence {1, −b}. This study provides comprehensive rules for designing periodic on–off waveforms and their references. The periodic waveform's high-average duty cycle (over 50%) makes it a ‘quasi continuous wave (CW) non-coherent waveform’, which avoids the pulse–train conflict between average power and unambiguous range. Good experimental results with a laser range finder are presented. Reports on other uses are quoted.

Perfect periodic cross-correlation is achievable in non-coherent pulse compression using Legendre sequences of any prime length. This paper briefly describes the (previously known) transmit and reference signals for the N = 4k − 1 case where N, the sequence length, is prime and k is a positive integer. It is then shown that a slight modification allows perfect periodic correlation with N = 4k − 3, doubling the number of available sequences.