Browsing by Author "Andre, Daniel"
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Item Open Access Analysis and exploitation of complex SAR phenomena produced from vibrating targets(Institute of Acoustics, 2018-12-31) Corbett, Brandon; Andre, Daniel; Muff, D.; Finnis, Mark V.; Blacknell, D.Item Open Access Bistatic 3D SAR for wall parameter extraction in cluttered environments(IET, 2021-07-28) Elgy, James; Andre, Daniel; Finnis, Mark V.Through-wall radar is an emergent technology rooted in urban surveillance, a key component being synthetic aperture radar (SAR). Accurate through-wall SAR relies on knowledge of the refractive index and thickness of any obscuring walls. Such information is rarely known beforehand and is subject to change on a sample-by-sample basis. It is therefore necessary to obtain the material properties in conjunction with any SAR measurement. In this letter, a remote data-driven asymmetric bistatic SAR approach is taken by means of matching the range to the direct back face reflection with an explicit geometry-based model. The proposed method relies on an accurate knowledge of the bistatic measurement geometry. Using the bright reflection from the front face of the wall, a method for refining an estimate of the bistatic measurement geometry is proposed. This approach is extended to three-dimensions to improve usability in heavily cluttered environments. This method is empirically validated using three-dimensional SAR measurements of both a wall-only, and a heavily cluttered scene. The method is shown to accurately extract both the refractive index and thickness of a concrete wall, with both measurements in agreement with each other and an independent validation measurement.Item Open Access Bistatic SAR for Building Wall Material Characterisation(Cranfield University, 2020-07) Elgy, James; Andre, DanielThis thesis addresses the problem of using radar to extract interpretable information concerning both the structure and electrical properties of a wall, and the environment behind it. This is broken down into two subproblems: how to determine the thickness and electromagnetic properties of the wall without being in direct contact with it, and how to obtain the most accurate images of what lies beyond the wall. Existing research in the area is evaluated and a theoretical study is presented on the use of monostatic, bistatic, and multistatic Synthetic Aperture Radar (SAR) in both one and two dimensional apertures. New methods of determining the wall properties are evaluated by both computer simulation and with laboratory radar measurements, where a wall of concrete blocks is constructed. The robustness of the asymmetric SAR geometry approach is evaluated with the addition of complex objects placed behind the wall. The uncertainty associated with estimating the wall properties is evaluated and consequential improvements to image quality are discussed. It was found that an asymmetric bistatic SAR geometry accurately extracts the refractive index and thickness of a wall. The method is applicable to both cluttered environments and non-parallel wall trajectories without loss of accuracy. Applying a compensation for refraction in the SAR imagery results in better positional accuracy but does not necessarily result in better image focusing. Volumetric multistatic image formation benefits from applied refraction compensation. SAR image formation, and in particular volumetric image formation, can be significantly accelerated via a spatially variant basebanding technique followed by zero padding. Spatially variant basebanding is sub optimal when applied to a Through-Wall radar scenario where there is a visible wall signature in the image. Keywords: Through-Wall radar, Multistatic radar, Multidimensional signal processing, Electromagnetic propagation, Radar imaginItem Open Access Combined intensity and coherent change detection with four classes for laboratory multistatic polarimetric synthetic aperture radar(Institution of Engineering and Technology (IET), 2024-06-14) Hagelberg, Alexander; Andre, Daniel; Finnis, MarkSatellites and drone swarms can be used to collect multistatic Synthetic Aperture Radar (SAR) images. Synthetic Aperture Radar images can be used for Intelligence Surveillance and Reconnaissance. One method is to use Coherent Change Detection (CCD) to identify changes such as objects or tracks in the scene. This paper investigates a two-stage change detector, formed using intensity change and CCD images, extended to laboratory measured multistatic SAR data. A variety of performance metrics are used to quantitatively assess the results. Bistatic results are compared to a variety of multistatic and fully polarimetric results. The improvement in performance of multistatic and fully polarimetric images over bistatic images is shown. Additionally challenges and limitations of using multistatic datasets are highlighted.Item Open Access Imaging SAR phenomenology of concealed vibrating targets(ADE (IEEE), 2018-08-16) Corbett, Brandon; Andre, Daniel; Muff, Darren; Morrow, Ivor L.; Finnis, Mark V.This paper describes the novel imaging of SAR phenomena produced from vibrating targets with multipath effects. It has been established, through numerical SAR experiments, that different physical mechanisms interact to produce new artefacts. The computations demonstrated that the edges of a dielectric medium can act as a source for multipath effects to emanate from, leading to the hypothesis that SAR artefacts can arise from through-wall SAR imagery. This deduction and mechanism of origin were validated through several experimental measurements, undertaken at Cranfield University’s Antennas and Ground-based SAR laboratory, yielding results that closely match those predicted.Item Open Access Laboratory bistatic synthetic aperture radar coherent change detection investigation(IET - The Institution of Engineering and Technology, 2023-08-10) Hagelberg, Alexander; Andre, Daniel; Finnis, MarkSynthetic Aperture Radar (SAR) Coherent Change Detection (CCD) allows for the detection of very small scene changes. This is particularly useful for reconnaissance and surveillance as small changes such as vehicle tracks can be identified. In some situations, it is desirable to rapidly collect repeat pass SAR images for use in change detection, and multistatic geometries may facilitate this. Such repeat passes may however have significant baselines, particularly for satellite-based platforms, though CCD products are reliant on high coherence for good interpretability. This work investigates the sources and levels of incoherence associated with bistatic SAR imagery with increasing baselines using simulations and measured laboratory data.Item Open Access Laboratory multistatic 3D SAR with polarimetry and sparse aperture sampling(Wiley, 2024-01-01) Welsh, Richard; Andre, Daniel; Finnis, MarkWith the advent of constellations of SAR satellites, and the possibility of swarms of SAR UAV's, there is increased interest in multistatic SAR image formation. This may provide advantages including allowing three-dimensional image formation free of clutter overlay; the coherent combination of bistatic SAR geometries for improved image resolution; and the collection of additional scattering information, including polarimetric. The polarimetric collection may provide useful target information, such as its orientation, polarisability, or number of interactions with the radar signal; distributed receivers would be more likely to capture any bright specular responses from targets in the scene, making target outlines distinct. Highlight results from multistatic polarimetric SAR experiments at the Cranfield University GBSAR laboratory are presented, illustrating the utility of the approach for fully sampled 3D SAR image formation, and for sparse aperture SAR 3D point-cloud generation with a newly developed volumetric multistatic interferometry algorithm.Item Open Access Laboratory multistatic polarimetric 3D SAR(IET, 2023-02-07) Andre, Daniel; Welsh, Richard; Finnis, MarkWith the advent of constellations of SAR satellites, and the possibility of swarms of SAR UAV's, there is increased interest in multistatic SAR image formation. This may provide advantages including allowing three-dimensional image formation free of clutter overlay; the coherent combination of bistatic SAR geometries for improved image resolution; the collection of additional scattering information, including polarimetric. The polarimetric collection may provide useful target information, such as its orientation, polarizability or number of interactions with the radar signal; distributed receivers would be more likely to capture any bright specular responses from targets in the scene, making target outlines distinct. Highlight results from multistatic polarimetric SAR experiments at the Cranfield University GBSAR laboratory are presented, illustrating the utility of the approach.Item Open Access Laboratory multistatic polarimetric sparse aperture 3D SAR investigation(Institute of Acoustics, 2023-12-31) Welsh, Richard; Andre, Daniel; Finnis, MarkSynthetic Aperture Radar (SAR) is a coherent technique that produces high quality imagery, with a finer cross-range resolution than would be possible with a stationary antenna. Radar pulses from multiple points along a flight path are combined, with return time and phase recorded for each pulse. This technique can be used to produce multidimensional 3D SAR images, with scatterers otherwise overlaid in range and azimuth separated out in height.Item Open Access Light Weight Low Cost X-Band Antennas and Waveguide Components Using Electroplated 3D Printed Plastics(Cranfield University, 2017-11-15 12:05) Wirth, Sebastian; Morrow, Ivor; Andre, Daniel; Finnis, MarkPoster presented at the 2017 Defence and Security Doctoral Symposium.Low weight and low cost are attractive features in many antenna and waveguide applications including mobile communication, remote sensing and medical scenarios. Electroplating shaped three-dimensional printed plastic components to produce highly conductive surfaces is one advantageous approach. This research contributes to the newly developed design procedure, manufacture and measurements of a 3D printed microwave pyramidal horn antenna electoplated with a 40 um copper coating and a novel flat 3D printed Graded Refractive Index (GRIN) lens. The antenna, waveguide and lens are printed in two pieces, the lens is then attached to the horn antenna aperture to provide a highly collimated radiated beam. Measurements conducted at Cranfield University Antennas and Ground Based SAR (AGBSAR) laboratory on the antenna matching radiated fields and gain demonstrate the performance meets, and in some cases exceeds, that of a standard X-band milled aluminium horn antenna and waveguide but with significantly reduced weight and cost. When the lens is attached to the horn antenna aperture an increase in antenna radiated gain of 5dBi over a 200 MHz bandwidth at 10 GHz is demonstrated. The hybrid antenna-lens sensor is highly suitable for near-field ground penetrating radar imaging of buried landmines. We acknowledge the financial support of the Sir Bobby Charlton Charity "Find A Better Way".Item Open Access Localising vibrating scatterer phenomena in synthetic aperture radar imagery(IET, 2020-01-21) Corbett, Brandon; Andre, Daniel; Finnis, Mark V.Artefact phenomena resulting from synthetic aperture radar (SAR) image formation can pose a challenge for image interpretation. One such artefact is produced when a vibrating target is imaged. Suppression of these artefacts has previously been described, however little has been developed in the area of modelling the location and shape of such artefacts. The authors present an experimentally validated model that provides accurate location and shape of vibrating target paired echoes in both SAR near-field and SAR far-field imagery.Item Open Access Low-frequency 3D synthetic aperture radar for the remote intelligence of building interiors(2017-06-12) Andre, Daniel; Faulkner, B.; Finnis, Mark V.Low-frequency (LF) synthetic aperture radar (SAR) images offer a viable approach to determining the architecture and contents of buildings and underground bunkers via remote sensing. Often however, standard 2D SAR images can be difficult to interpret due to component signatures from different heights being projected into the scene leading to confused results. In this research, measurement results have shown that the full Nyquist 2D aperture scan approach to 3D through-wall LF SAR provides focussed 3D resolution of a wall and contents behind it in a number of frequency bands. Full-scale radar system upgrades are ongoing in order to investigate numerous other scenarios, however in the meantime, sparse 2D aperture scanning investigations have been undertaken with a prototype radar scanner. Whilst this kind of collection cannot achieve the low sidelobe levels of full Nyquist 2D aperture collections, these prototype scanner measurements are much faster to collect, and have shown encouraging results of sufficient image quality to determine the 3D configuration of prominent features in the target scene, albeit with higher sidelobe or image artefact levels.Item Open Access Microwave phase contrast imaging of the subsurface using variation in soil moisture level(IEEE, 2018-10-25) Wirth, Sebastian G.; Morrow, Ivor L.; Andre, DanielA new microwave subsurface imaging product is described which is evolved via time lapsed microwave measurements, over several days, of the soil subsurface. The technique exploits changes in soil moisture levels that occur naturally due to evaporative and percolation processes. A novel technique is investigated for detecting and discriminating buried targets; it provides a scaled phase weighting procedure to form a cumulative B-scan image of the subsurface. The algorithm is demonstrated on ground penetrating radar measurements acquired in the XBand spectrum over soil where reference targets and other buried artefacts are placed. Early stage experimental results suggest the approach shows promise to provide enhanced subsurface imagery with reduced clutter and noise levels.Item Open Access Multistatic 3D SAR imaging with coarse elevation and azimuth sampling(IEEE, 2022-11-10) Welsh, Richard; Andre, Daniel; Finnis, MarkIt is advantageous to produce Synthetic Aperture Radar (SAR) renderings in three dimensions as these allow the separation of features in height, providing additional target information. A Nyquist sampled 2D SAR aperture produces high quality 3D imagery, however the large scanning time and data storage requirements make this method impractical for use in many scenarios. This paper investigates the formation of 3D target renderings from sparsely sampled 2D aperture Multistatic SAR geometries. The investigation employed both simulations and measured multistatic data collected at the Ground Based SAR (GBSAR) Laboratory at Cranfield University.Item Open Access Multistatic dual-polarimetric through-wall 3D-SAR(IEEE, 2021-07-02) Andre, Daniel; Watson, Francis; Finnis, Mark V.Through-wall (TW) imaging is of great interest for both military and civilian applications. At sufficiently low radar frequencies, Synthetic Aperture Radar (SAR) provides a TW sensing solution, however making sense of cluttered and overlaid signatures can prove difficult. This work investigates the suitability of three-dimensional dual-polarimetric multistatic TW-SAR, for the determination of building architectures and the detection of targets within buildings. These results are relevant to radar sensing Unmanned Air Systems under current developmentItem Open Access Multistatic hybrid SAR/ISAR data generation using a stationary target(IET - The Institution of Engineering and Technology, 2023-02-07) Rattan, Anmol; Andre, Daniel; Finnis, MarkThere is great interest in multistatic synthetic aperture radar (SAR) systems as they are capable of providing high resolution images. These systems could prove promising candidates for provision of surveillance for both military and civilian interest. Both multistatic SAR and its counterpart, multistatic inverse synthetic aperture radar (ISAR), are limited by their assumptions of observing a stationary target from a moving platform and vice-versa. Hence, without adequate target motion compensation, their resultant radar images appear defocused. Arranging experiments capable of providing repeatable multistatic hybrid SAR/ISAR data of real moving targets can be difficult and costly. One viable approach is the novel method presented in this study, whereby multistatic hybrid SAR/ISAR data can be collected of a target moving with a theoretical motion, without the requirement of an actual moving target – the theoretical motion is brought about through the appropriate motion of antennas. The study demonstrates, both through simulation and experimentation, how radar trajectories of a given SAR system can be altered to arrive at the equivalent setup of observing a moving target. Results from simulation and from an experiment conducted at the Cranfield University Ground-Based SAR (GBSAR) laboratory are presented, showing the utility of this approach.Item Open Access Near-Field Virtual Bandwidth Synthetic Aperture Radar Processing for Humanitarian Landmine Detection(Cranfield University, 2017-11-15 11:56) Wirth, Sebastian; Morrow, Ivor; Andre, Daniel; Finnis, MarkPoster presented at the 2017 Defence and Security Doctoral Symposium.This research presents the first experimental demonstration of the Near-Field Virtual Bandwidth SAR (NFVB-SAR) imaging technique. NFVB-SAR is a newly developed sub-surface imaging technique which in contrast to traditional imaging techniques promises subsurface imaging of soils at ultra-high, centimetre-scale resolution using narrow bandwidth. We specifically exploit the differential interferometric SAR phase history of an electromagnetic wave within a drying soil volume to generate high resolution sub-surface mapping from the returned wave through the soil volume. Experiments were conducted at the Cranfield University Antennas and Ground Based SAR (AGBSAR) laboratory using a near-field full polarimetric data acquisition ground penetrating radar. Measurements were taken over a sandy soil containing a buried landmine while the moisture level was varied. - firstly during controlled water addition and then during an extended natural drying out period. As the sand volume dries, the real radar frequency is sequentially transported across a virtual bandwidth of virtual frequencies. The preliminary results demonstrate that even a moderate soil moisture change (SMC) can produce large virtual bandwidths; for e.g. an SMC change of 10% can provide 6cm vertical resolution at X-band. We acknowledge the financial support of the Sir Bobby Charlton Charity "Find A Better Way",10.17862/cranfield.rd.5585245.v1.Item Open Access Non-overlapping trajectory Multistatic SAR Coherent Change Detection(IET, 2022-04-21) Hagelberg, Alexander; Andre, Daniel; Finnis, MarkSynthetic Aperture Radar (SAR) Coherent Change Detection (CCD) allows the detection of very small scene changes but is typically reliant on a high degree of similarity in the radar trajectories, with a small baseline. In the case of multistatic SAR imagery, such as those formed by a constellation of SAR satellites, the radar trajectories may have a greater baseline than those collected by a monostatic system such as an aircraft. This paper investigates the effects of multistatic trajectories on the measured coherence between imagery, and how this relates to the spatial frequency (K-space). In particular, the case where radar platform trajectories are greatly dissimilar, but where the K-space image supports still contains a high degree of overlap, is investigated. This paper uses multistatic SAR collections measured at the Ground Based SAR Laboratory at Cranfield University.Item Open Access Polarimetric bistatic SAR image coherence(VDE Publishing, 2022-11-10) Hagelberg, Alexander; Andre, Daniel; Finnis, MarkSynthetic Aperture Radar (SAR) Coherent Change Detection (CCD) allows the detection of very small scene changes, such as from ground subsidence or vehicle tracks, with applications both civilian and military. This high sensitivity to small changes can mean that differences in collection geometry or in polarisation can lead to significant changes in image coherence. This paper investigates the coherence between different bistatic SAR image geometries and their corresponding spatial frequency supports. It also investigates methods used to model coherence. The investigation employed both simulations and measured multistatic data collected at the Ground Based SAR Laboratory at Cranfield University.Item Open Access Radar geometries used during the PhD of Alexander Hagelberg(Cranfield University, 2024-08-23) Hagelberg, Alexander; Andre, DanielThis excel file contains the co-ordinates used in the experiments of the PhD of Alexander Hagelberg. These trajectories were used in various papers which are listed in the headers.