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In this Letter, the authors propose using compressive sensing (CS)-based Stolt migration imaging approach to reduce the amount of measurement data and provide an enhanced imaging quality. The authors utilise both forward and backward Stolt migration imaging operators to deal with the measurement and image the space data in two-dimensional matrix form for sparse recovery computation. This imaging process accounts for the electromagnetic wave propagation and does not require prior knowledge of the transmitted pulse, which is practically not available in practice. Results of the proposed numerical simulation demonstrate the validity and effectiveness of the proposed imaging algorithm.

Pulse-agile radar systems are becoming more prevalent as the demand for adaptive and cognitive systems increases. This focus is motivated by the need for interference avoidance and spectrum sharing. Pulse agility within a coherent processing interval (CPI) or intra-CPI adaption has been shown to cause distortion, which will negatively impact the radar's performance. This problem can be framed in the context of image processing such that an ideal range-Doppler image is corrupted by some point spread function. Deconvolution is then applied to remove this distortion and improve radar performance while maintaining the ability to use computationally efficient fast Fourier transform-based processing.

Highly sampled imagery offers many benefits to the radar practitioner, ranging from easier image coregistration to simple visual appeal. However, it is often overlooked due to the computational burden forming such an image imposes. Fast image formation typically imposes restrictions on the imaging scenario, for example synthetic aperture radar (SAR) far-field, and exploits parallelism through use of modern multi- core architecture. Imposing a SAR near-field requirement on the image formation limits the applicability of several of the faster algorithms, thus there is a need to create a general process to achieve highly sampled imagery, regardless of the imaging regime. In this letter, a method for accurately upsampling near-field (SAR) imagery is presented. This is applicable to both SAR near-field and SAR far-field scenarios. The methodology is discussed, and an example is provided in the form of a SAR near-field volumetric image of a miniature tank. The limitations to the approach are discussed and prospects for future work given.

Tomography SAR (TomoSAR) imaging can achieve three-dimensional (3D) imaging, which is significant for urban 3D mapping. When the baseline of TomoSAR is sparse, the scattering centres of several different altitudes in the same resolution unit are aliased together, which affects the accuracy of TomoSAR imaging. To solve this problem, an altitude ambiguity suppression method based on dual-frequency interfering and multi-frequency averaging is proposed. Firstly, dual-frequency interfering is used to obtain the radar cross-section (RCS) of targets and the sum of the results of the cross interference between targets and ambiguities in different positions. Then multi-frequency averaging is used to suppress the power of the cross-interference, and finally the RCS of target is accurately obtained. Simulation results verify the effectiveness of the proposed method.

For the synthesised aperture radar, the radar signal with a zero autocorrelation zone (ZACZ) is synthesised, which represents a sequence from two phase-code shift keying (PCSK) pulses coded by adjacent pairs of the D-code with additional linear frequency shift-keying (LFSK) of the train pulse discrete value. A comparative analysis is performed of correlation characteristics of the synthesised signal with the signal without discrete modulation and the truncated M-sequence. Total correlation characteristics of the ensemble from four signals are also analysed. It is shown that in ZACZ, the level of all side lobes of the autocorrelation function (ACF) of the synthesised signal is less than the level of the ACF side lobes of the M-sequence. The total ACF of the ensemble of four signals both with modulation and without the discrete modulation has zero side lobes along with the whole time axis τ, and at mismatch in frequency in ZACZ, it has the side lobe level

A novel target recognition method is proposed for high-range resolution profiles (HRRPs) of radar targets under low signal-to-noise ratio (SNR) conditions. This method achieves good recognition performance for noisy HRRPs with discriminative sparse-low-rank representation. The framework of this method is constructed based on sparse representation and low-rank representation, which are applied to extract the local and global characteristics of target HRRPs. To guarantee the noise-robust and highly discriminative features of the HRRPs, dictionary learning is adopted. In the training stage, a discriminative dictionary is produced based on hinge loss theory to improve the recognition performance. Denoising dictionary optimisation is implemented for noise suppression during the testing stage. Experimental results on measured HRRP data demonstrate that the proposed method can recover the original HRRPs and significantly improve the recognition performance for HRRP test samples under relatively low SNR conditions.

Transient interference cancellation is necessary for high-frequency sky-wave radar and usually requires accurate interference detection and localisation which is complicated due to the non-uniform noise level caused by sea-clutter mitigation in Doppler domain. A novel approach is proposed by converting the detection of interference into a problem of straight line extraction in the constructed fast- and slow-time images. The line edges are detected by an edge detector, such as Canny method, followed by Hough transform. Then, each edge is classified as a rising, falling or false-alarm edge based on multi-threshold segmentation of image sub-blocks. Experimental results demonstrate the effectiveness of the proposed approach.

A knowledge-aided mono-pulse forward-looking imaging algorithm to enhance the performance of airborne radar is proposed. Firstly, the ideal mono-pulse imaging model based on the dual-channel radar system is analysed and the mismatch model of the receiving channel is constructed. Then the mismatch phase error and a modified mono-pulse curve (MPC) are derived based on the least square (LS) method by taking advantage of a prior antenna pattern information. Finally, the modified MPC is utilised to perform the direction-of-arrival (DOA) estimation of each scattering centres in mono-pulse imaging. Real airborne radar data experiments are given to verify the effectiveness of the proposed algorithm.

A new feature named ‘2D comb’ to improve ship classification is proposed. The proposed feature presents added value to distinguish between container ship, tank ship and cargo ship. It is based on radar cross-section (RCS) statistic of the ship target related to the ship structure. Besides, related local RCS is proposed to classify three kinds of ships. Experimental results based on TerraSAR-X images show that the proposed feature can abstract and describe the ship structure in high-resolution synthetic aperture radar (SAR) imagery. It establishes relationship between RCS and ship structure, which is very useful to distinguish different kinds of ships.

Sparse reconstruction has been recently proposed to overcome many challenges in radar imaging applications. In sparse reconstruction framework, the basis matrix of high-resolution radar image demonstrates high mutual coherence, which is inversely proportional to the quality of the reconstructed image. The high mutual coherence, also, weakens the noise immunity in the sparse reconstruction. A technique for building a basis matrix with low mutual coherence is proposed which preserves the high quality of the resultant radar image. The proposed technique groups the columns of the original basis matrix that share the same range of time delay into one column with the average time delay of the group. The resultant basis matrix is used in a sparse reconstruction algorithm to reconstruct the pixel values of a radar image. The technique was validated over realistic and simulated radar measurements and was shown to be computationally efficient with improved noise immunity.

The terahertz (THz) radar has obvious advantages of high-resolution imaging because it is relatively easy to achieve large signal bandwidth compared with the microwave band. A 0.33 THz imaging radar system was built and experiments on a precession warhead model are presented. The imaging algorithm based on precession is adopted and high-resolution inverse synthetic aperture radar images are obtained. From these imaging results, the structures such as the cone-top and the cone-cylinder junctions, and even the subtle structures such as rivets are clearly shown. Finally, the resolutions under different conditions are analysed to verify the advantages of THz radar in high-resolution imaging.

ArcSAR is a Synthetic Aperture Radar which recently has been receiving increasing interest in scientific literature. It operates exploiting the spatial diversity of the data acquired by an antenna fixed to a rotating arm. Its great advantage is its capability to synthesise images at 360° with constant resolution in azimuth. The ArcSAR, in addition to operate as interferometric differential radar, can detect the elevation of the targets, i.e. it is potentially able to generate digital elevation models of the surrounding field of view.

A moving train was imaged by a Ka-band interferometric (In) radar of 2 GHz bandwidth working at the dechirping model. Two radar images from two channels as well as their In image were obtained after estimating the speed and direction of the train. The plots of In phases (InPhes) along the train exhibits periodic fluctuations, which are resulted from the back and forth motions of both locomotive and other compartments when the trains are moving ahead, and this can be attributed to the micro-motion (m-M) of the train. As far as it is known, this is the first time to experimentally demonstrate m-M detection through InPhes.

Radar research using transmitters of opportunity (commensal radar (CR)) has experienced a resurgence in popularity. Most published results to date used a multiple transmitter, single receiver site configuration with combinations of bearing, range and Doppler for target localisation. Doppler-only tracking has received the least attention. This reported work demonstrates with field measurements, using a single frequency modulation broadcast radio transmitter and multiple, spatially distributed, low-cost CR receivers, that Doppler-only tracking is achievable with target position accuracies of 150 m, despite a course range resolution.

The frequency modulated continuous-wave (FMCW) technique has been used in many radar applications owing to its low requirements on radar hardware. Linear sawtooth sweep (the frequency sweeps in one direction) is one of the simplest waveforms employed by most FMCW radars. By theory and real data it is proved that by simply using the linear triangular sweep (the frequency goes first down and then up), the range resolution can be doubled without increasing the transmitted bandwidth.

A novel method employing two-dimensional (2D) unitary ESPRIT and a spatial smoothing technique is proposed for super-resolution ISAR imaging. The spatial smoothing technique is employed to resolve the contradiction that 2D unitary ESPRIT requests multiple snapshots; however, in radar imaging applications only one snapshot of the radar data are available. Experimental results are presented to verify the high resolution and feasibility of the proposed imaging algorithm in ISAR imaging.

A design consideration for super-Nyquist frequency modulated continuous-wave (FMCW) radar systems relating to transmitter to receiver noise leakage is introduced. Phase noise curves comparing the fundamental direct digital synthesisers frequency and its second super-Nyquist image show a significant increase in relative noise level at all offsets from the carrier. This results in a reduced transmitter signal-to-noise ratio. It is shown with a simple example that this can lead to a significant degradation in receiver sensitivity if not managed properly. A design rule-of-thumb that can be used by radar designers to avoid or mitigate this problem is provided.

Airborne circular stripmap synthetic aperture radar (CSSAR) has the advantages of short revisit time and large coverage, and thus is an attractive tool for wide area surveillance. A novel ground moving target imaging algorithm for single channel airborne CSSAR is proposed. The proposed algorithm can be implemented without knowing a target’s motion parameters. Simulation results indicate that moving targets can be well focused by the proposed algorithm.

A new method for three-dimensional (3D) imaging via a narrowband bistatic multiple-input-multiple-output (MIMO) radar with two uniform rectangular arrays is presented. After matched filtering and phase compensation, the method utilises the 2D cross-range images measured by the transmit and receive arrays to reconstruct the 3D image of the target. Compared with the 3D wideband monostatic MIMO imaging, lower hardware cost can be achieved since the narrowband waveforms are employed. In addition, the range alignment in wideband imaging can be avoided for the poor range resolution of the narrowband waveforms.

Passive radars utilising illuminators of opportunity are being actively studied in the field of radar. In the last few years, many illuminator sources have been employed for passive radar applications. However, there have been no published results on the use of the long-term evolution (LTE) signal as a novel source for passive radar applications. For the first time an experimental investigation into the feasibility of LTE-based passive radars for detecting a moving target is presented. A theoretical analysis was conducted on a captured LTE signal in the atmosphere. This was then followed by a field experiment. The preliminary results show that the LTE signal is capable of being an illuminator for passive radars.

Forward imaging radar using an UWB signal has been developed by many researchers. The image quality in this radar is not satisfactory because of the limitation of aperture length. Proposed is an image enhancement method using a modified apodisation technique in forward imaging radar. An experiment is carried out to validate the proposed method. The azimuth resolution and peak-to-sidelobe ratio are improved by the proposed method by up to about 11.7% and 10 dB, respectively.

Prominent point processing (PPP) is a very popular synthetic aperture radar (SAR) autofocus algorithm, which can estimate errors caused by any type of unknown motion or other error source and has high accuracy under the assumption that a prominent point scatterer is available within an imaged scene. Proposed is an advanced PPP algorithm with a preprocessing technique based on the short-time fractional Fourier transform (STFRFT) to relax the limitation on the scene content. The performance of the proposed autofocus algorithm is validated using real radar data.

Compared with sequential single-input–multiple-output array, a novel design method of high-efficiency sparse array is proposed to achieve the similar azimuth resolution and lower grating-lobe level. Theoretical analysis and numerical experiments demonstrate that the designed array is irredundant and the efficiency is increased. The work can benefit the development of high-resolution imaging and low-cost ultra-wideband radar.

A report is presented on results achieved with an FM band commensal radar system in which the surveillance and reference antennas are widely separated, making use of common view, Global Positioning System disciplined oscillators to maintain timing synchronicity. The proposed configuration allows greater DPI suppression by means of terrain shielding and independent selection of the surveillance receiver position to enhance target visibility.

The issue of extracting micro-Doppler (mD) information of the coning target radar echoes with or without Doppler aliasing is considered using scattering centre reconstruction combined with the time-frequency analysis (TFA) method. The effectiveness of the presented method is investigated using real measured radar signal experiments. For radar echoes without Doppler aliasing, extraction of the mD information of the coning target using traditional TFA can be obtained. However, using the presented method the mD information is more precise. For radar echoes with Doppler aliasing, there are significant differences in precision between the traditional TFA and the presented methods, and the mD information is smeared using the traditional TFA. Nevertheless, the extraction of mD information can be achieved by the presented method.

A linear frequency-modulated continuous-wave (LFMCW) radar with a simplified single homodyne channel is proposed and developed in the 0.22 THz band. The transmitter employs direct digital waveform synthesiser technology to obtain a reliable fast scanning LFMCW source, the scanning speed of which is 40 µs with an instantaneous bandwidth of 14.4 GHz. To realise the nonlinearity calibration and coherent imaging, the quadrature signal is recovered by a Hilbert transform receiver to obtain the phase information of the return wave. The radar operates using the real-aperture imaging method and uses a lens to focus the Gauss beam which determines the azimuth resolution. The results of the pulse compression and imaging experiments verify the effectiveness of the proposed imaging scheme in the 0.22 THz band. The radar can be used for non-destructive testing and security checks.

A method is proposed for estimating the target rotation rate for ISAR imaging based on the frame processing technique. The method utilises the intrinsic structures of the frame which span the Hilbert space of radar return from which the rotational information of the target is extracted. For a prominent point, the intensity of the projection is maximum when the frame component corresponding to the prominent point is built with the target rotation rate.

Introduced is radar and sonar echoic flow as the counterpart to its better-known cousin, optical flow. Echoic flow can be computed in a number of forms, the simplest being the ratio of range to range rate. This provides a direct measure of the time to collision between a radar/sonar system and a detected object. Its derivative is a measure of collision intensity. Thus, together, these two quantities provide a powerful basis for autonomous navigation and related applications. The origins of echoic flow are explained and it is shown through simulation how it can be used as a basis for radar-based autonomous navigation.

The microwave Doppler radar sensor enables a non-contact approach for measuring movement in various applications. One of the most challenging issues is radar signal demodulation because it requires accurate DC offset compensation. Existing works either require a complicated setup procedure or are sensitive to environmental changes. In this reported work, a compressed sensing based approach to effectively demodulate a radar signal is discussed. Through l 1 minimisation, the proposed method can reliably demodulate noisy signals with large measurement residuals. To validate the algorithm, three sets of experiments were run to evaluate the demodulation performance. Experimental results show that the proposed method is promising in both simulation and real-case studies.

A wavelet transform focuses on localised signal structures with a zooming procedure that progressively reduces the scale parameter. On the other hand, fractal geometry has recently been applied to the analysis of high range resolution radar sea clutters. Using both concepts in designing a new detector, reveals considerable improvement in performance of target detection within sea clutter. In support of this argument, simulation results using real radar data samples are presented.

An efficient method is presented to extract the active distortions of polarimetric radar systems without the measurement of a point calibration target under field conditions. The active distortions are extracted using the signal returned from the antenna input. The backscattering coefficients of distributed targets measured using the proposed method agree quite well with results of numerical simulations and spaceborne SAR measurements.

The range migration of airborne forward-looking scanning radar is first analysed, and then the keystone transform is introduced to correct the space-variant range migration. Finally, deconvolution is conducted to obtain the super-resolution image. Simulations are given to verify the effectiveness of the method.

The probability model of multipath delays is proposed for scattering centres above the ocean surface. The surface is endowed with the Kirchhoff approximation, as well as a probability density function of the elevations and slopes. The model faithfully reflects the stochastic character of the multipath delays in imaging radar echoes. Moreover, it explores a way to simulate the synthetic aperture radar images without the time-consuming process of electromagnetic computation.

An experimental radar at 220 GHz has been developed which is capable of delivering an instantaneous bandwidth of 8000 MHz. The solid-state radar uses an FM-CW waveform. The development is based on experience with a 94 GHz broadband measurement radar. The data undergo an ISAR imaging process to derive high-resolution scattering centre distributions for targets measured in tower/turntable configuration. High-resolution processing algorithms have been developed which result in scattering centre distributions with a resolution better than 2 cm at ranges of and exceeding 200 m. The radar will be used for investigations on target signatures of small objects for stand-off detection of concealed weapons and other threat material.

A low-complexity radar for human tracking in three-dimensional space is reported. The system consists of a three-element receiving array and two continuous-wave (CW) frequencies configured to provide azimuth bearing, elevation bearing and range measurements. Doppler processing is used for clutter removal as well as to separate multiple moving targets. A radar prototype is constructed and tested. Three-dimensional tracking of multiple humans is performed in both unobstructed and through-wall scenarios.

A two-dimensional Doppler and direction-of-arrival (DDOA) radar concept is proposed for the frontal imaging of humans. The system consists of a three-element receiver array configured to provide simultaneous DOA measurements in the azimuth and elevation planes. An experimental system has been built and tested. Two-dimensional frontal images of a human in free space as well as in a through-wall scenario are generated.

Microwave breast cancer detection is based on the differences in electrical properties of malignant tumours and normal fatty tissues. Radar-based approaches involve interpreting information in ultra-wideband reflections from the breast. A key issue in the design of radar-based tumour detection systems is selection of a substance to couple the breast and antenna. Several liquids are compared and the benefits of selecting an oil-based immersion liquid are shown.

A new continuous-wave linear frequency modulated radar scheme, which allows the accomplishment of high resolution radar images independently of the target position, is presented. Range resolutions around 15 cm can be achieved transmitting a gigahertz of bandwidth with a maximum distance of 15 km.

Success of a phase unwrapping algorithm for radar interferometry depends on availability of a good quality map. Many quality map extraction algorithms are available, and most methods use a fixed window around each pixel. When there are noise corrupted pixels, the fixed window sometimes yield poor results, and so a weighted window is proposed for use for quality map extraction.

Due to the presence of relatively large amounts of noise, co-registration of SAR images typically involves matching of local area based `tie patches' rather than feature based `tie points'. Some applications require small tie patch windows e.g. stereo SAR. Small tie patch windows, however, can lead to poor estimates of the local co-registration parameters. This paper proposes a procedure to minimise the ie patch window size while retaining `confidence' in the local co-registration result. Background theory to the procedure and the results of an experimental study are resented.

A new adaptive radar target detection algorithm which is of significant use in nonhomogeneous clutter environments is developed. The key idea of the proposed algorithm is that the degree of freedom is controlled to avoid a serious detection loss due to limited secondary data vectors, while maintaining high performance of the joint polarisation-space-time processing. The performance of the proposed algorithm is numerically evaluated to illustrate its efficiency in limited secondary data environments.

Radar space-time adaptive processing (STAP) techniques characteristically offer adaptivity in Doppler and azimuth. This research extends STAP concepts by incorporating elevation adaptivity using a two channel vertical interferometer. Using multi-stage processing and measured airborne radar data, clutter suppression improvement of 15 dB is achieved.

The use of switched circular transmission in polarisation diversity radar enables an estimate of apparent canting angles in rain to be obtained. Results are presented from an X-band radar in Ottawa.

The total phase measured from a polarisation-diversity radar is the sum of differential propagation phase and backscatter phase. An algorithm is presented to obtain differential propagation phase from the total phase by separating the back-scatter phase. This algorithm is independent of raindrop size distribution and frequency.

Based on the pseudorange correction adopted in GPS (global positioning system), the round-trip propagation range for a monostatic radar is derived. By treating the Doppler effect as the time rate of chance of the propagation range, the radar Doppler shift is generalised to the case where the velocity of the target relative to the transceiver is arbitrary, thereby taking into account both the transverse component of the relative velocity and the acceleration.

A two-mode radar altimeter on board a cost-effective microsatellite is proposed for sea state monitoring. The new additional low resolution mode is used to achieve improved normalised radar cross-section /spl sigma//sup 0/ measurement with the antenna having an off-nadir look angle up to 0.5/spl deg/.

The authors propose an interferometric radar system for the remote monitoring of structural deformations in buildings. A continuous wave step frequency (CW-SF) radar is used to synthesise radar cross-section (RCS) holographic images. The monitoring radar has been experimentally validated during a structural static test of a concrete pedestrian bridge.

The authors propose a ground-based interferometric radar for terrain elevation mapping. The radar is of the continuous-wave step-frequency (CW-SF) type and it operates by synthesising pairs of microwave holographic images taken at different antenna heights to obtain elevation maps by phase comparison.

Sequential transmission from the elements of a 2D array, with parallel reception and recording by all, permits major economies in transmitted and irradiating power, and provides significant novel processing options for much improved performance in the face of noise or clutter.