CERES :: Browsing by Author "Finnis, Mark"

Browsing by Author "Finnis, Mark"

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Open Access
Aero-whisker for the measurement of aircraft flight speed and angle of attack in compressible flow conditions
(AIAA, 2023-06-08) Debiasi, Marco; Atkinson, Kevin; Saddington, Alistair J.; Finnis, Mark
A whisker-like device has been designed and tested that simultaneously measures the speed and the direction of a flow in which it protrudes. The device consists of a thin cylindrical probe longer than the thickness of the local boundary layer whose aerodynamic drag produces a moment at its base which is measured by a solid-state torque transducer. With proper calibration, the orthogonal components of the moment can be used to measure the speed and the direction of the flow. Measurements have been performed in a wind tunnel to validate the design at flow velocities ranging from Mach 0.15 to Mach 0.87 and for flow angles relative to the probe ranging from -88° to +88°. The results obtained indicate that the aero-whisker is capable to accurately measure the Mach number and direction of the flow with potential for further optimization for aircraft applications.
Open Access
Bistatic multi‐polarimetric synthetic aperture radar coherence investigation using spatially variant incoherence trimming
(Institution of Engineering and Technology (IET), 2024-12-31) Hagelberg, Alexander; Andre, Daniel; Finnis, Mark
Synthetic Aperture Radar (SAR) Coherent Change Detection allows for the detection of very small scene changes. This is particularly useful for Intelligence, Surveillance and Reconnaissance as small changes such as vehicle tracks can be identified. Rapidly collecting repeat pass SAR imagery is important in these applications. For space‐borne platforms, such repeat passes may however have significant differences, or baselines. Coherent Change Detection products are reliant on high coherence for good interpretability. This work investigates the sources and levels of incoherence associated with bistatic SAR imagery for a variety of baselines using simulations and measured laboratory data for two ground types. Additionally, spatially variant incoherence trimming is implemented. The paper shows the importance of angle‐dependant backscatter on the coherence of sub‐resolution cell scatterers.
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, Mark
Satellites 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.
Open Access
Laboratory bistatic synthetic aperture radar coherent change detection investigation
(Institution of Engineering and Technology (IET), 2023-08-10) Hagelberg, Alexander; Andre, Daniel; Finnis, Mark
Synthetic 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.
Open Access
Laboratory multistatic 3D SAR with polarimetry and sparse aperture sampling
(Wiley, 2024-01-01) Welsh, Richard; Andre, Daniel; Finnis, Mark
With 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.
Open Access
Laboratory multistatic polarimetric 3D SAR
(IET, 2023-02-07) Andre, Daniel; Welsh, Richard; Finnis, Mark
With 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.
Open Access
Laboratory multistatic polarimetric sparse aperture 3D SAR investigation
(Institute of Acoustics, 2023-12-31) Welsh, Richard; Andre, Daniel; Finnis, Mark
Synthetic 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.
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, Mark
Poster 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".
Open Access
Modelling real‐world effects in near‐field SAR collections for compressive sensing
(Institution of Engineering and Technology (IET), 2025-01) Price, George A. J.; Andre, Daniel; Moate, Chris; Yuen, Peter; Finnis, Mark
The ability to control sidelobes in a SAR image is critical to forming images that are useful for interpretation and exploitation. QinetiQ has developed the RIBI sensing system, which utilises a distributed coherent array of sensors to produce multistatic images. These systems require techniques from outside the traditional radar domain to utilise the theoretical resolution possible in synthesising a coherent aperture from multiple disparate collections. This paper develops previously published work on using compressive sensing techniques to suppress sidelobes in SAR images to develop a higher‐fidelity measurement model. Using Cranfield University's GBSAR System a series, experimental measurements are conducted, and image estimation techniques are applied to this real data. It demonstrates an improvement in recovery performance over an isotropic measurement matrix, and discusses areas which require further development.
Open Access
Multistatic 3D SAR imaging with coarse elevation and azimuth sampling
(IEEE, 2022-11-10) Welsh, Richard; Andre, Daniel; Finnis, Mark
It 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.
Open Access
Multistatic hybrid SAR/ISAR data generation using a stationary target
(Institution of Engineering and Technology (IET), 2023-02-07) Rattan, Anmol; Andre, Daniel; Finnis, Mark
There 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.
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, Mark
Poster 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.
Open Access
Non-overlapping trajectory Multistatic SAR Coherent Change Detection
(IET, 2022-04-21) Hagelberg, Alexander; Andre, Daniel; Finnis, Mark
Synthetic 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.
Open Access
Polarimetric bistatic SAR image coherence
(VDE Publishing, 2022-11-10) Hagelberg, Alexander; Andre, Daniel; Finnis, Mark
Synthetic 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.
Open Access
Polarimetry for sparse multistatic 3D SAR
(Institution of Engineering and Technology (IET), 2025-01-01) Welsh, Richard; Andre, Daniel; Finnis, Mark
There is significant interest in multistatic SAR image formation, due to the increased development of satellite constellations and UAV swarms for remote sensing applications. The exploitation of the finer resolution and wider coverage of these geometries has been shown to reduce the often‐impractical data collection requirements of 3D SAR imagery; this offers advantages such as improved target identification and the removal of layover artefacts. This paper presents a novel polarimetric generalisation of the SSARVI algorithm, which was previously developed to exploit sparse aperture multistatic collections for 3D SAR image formation. The new algorithm presented here, named the PolSSARVI algorithm, combines polarimetrically weighted interferograms for determining the 3D scatterer locations from sparse aperture polarimetric collections. The bistatic generalised Huynen fork polarimetric parameters are then determined for the multistatic PolSSARVI 3D SAR renderings. This new approach was tested on both simulated and experimental data. Experimental imagery was formed using measurements from the Cranfield GBSAR laboratory.
Open Access
Synthetic Aperture Radar for Through-Wall Detection and Imaging of Complex Vibrating Targets
(Cranfield University, 2017-11-15 11:56) Corbett, Brandon; Andre, Daniel; Muff, Darren; Morrow, Ivor; Finnis, Mark
Poster presented at the 2017 Defence and Security Doctoral Symposium.Low frequency Synthetic Aperture Radar (SAR) is a proven solution for generating through-wall images, although obtaining a clear picture of the structure and contents of buildings has proven to be difficult. Whilst the effects created by moving objects within a SAR image have been investigated before, the complex effects moving objects have upon a SAR image when located behind a wall, are less known. This is especially the case when the motion of the object being imaged is of vibration and when multipath effects influence the artefacts produced within the SAR image. This occurs when the transmitted SAR microwaves reflect from other objects within the imaged scene, before being detected by the receive antenna. The research presented, investigates these complex SAR phenomena with multistatic radar geometries, using the Cranfield University Antennas and Ground Based SAR (AGBSAR) laboratory. This research is conducted in support of the Dstl Remote Intelligence of Building Interiors (RIBI) programme, and addresses the problem of the detection of running machinery within buildings, amongst other challenging scenarios.
Open Access
Through-wall multistatic polarimetric 3D SAR
(VDE Publishing, 2022-11-10) Andre, Daniel; Sabiers, Richard; Finnis, Mark
Through-Wall (TW) Synthetic Aperture Radar (SAR) imagery can be difficult to interpret due to several factors including signal attenuation in highly cluttered environments, target overlay, difficult to interpret low SAR resolution and low frequency scattering responses. One approach which may help improve image interpretability is to employ 2D SAR apertures with multiple distributed receivers in all polarizations. For example: a 2D SAR aperture would allow the formation of 3D images, reducing noise levels and clutter overlay, as well as improving the recognition of objects through providing height information; the distributed receivers would be more likely to capture any bright specular responses from targets in the scene, making them visible; the polarimetric collection may provide useful target information, such as its orientation, polarizability or number of interactions with the radar signal. Highlight results from TW-SAR bistatic polarimetric experiments at the Cranfield University GBSAR laboratory are presented, illustrating the utility of the approach.
Open Access
Through-wall multistatic polarimetric 3D SAR
(NATO Science and Technology Organization, 2022-06-12) Andre, Daniel; Sabiers, Richard; Finnis, Mark
Through-Wall (TW) Synthetic Aperture Radar (SAR) imagery can be difficult to interpret due to several factors including signal attenuation in highly cluttered environments, target overlay, difficult to interpret low SAR resolution and low frequency scattering responses. One approach which may help improve image interpretability is to employ 2D SAR apertures with multiple distributed receivers in all polarizations. For example: the 2D SAR aperture would allow the formation of 3D images, reducing noise levels and clutter overlay, as well as improving the recognition of objects through providing height information; the distributed receivers would be more likely to capture any bright specular responses from targets in the scene, making them visible; the polarimetric collection may provide useful target information, such as its orientation, polarizability or number of interactions with the radar signal. Highlight results from TW-SAR bistatic polarimetric experiments at the Cranfield University GBSAR laboratory are presented, illustrating the utility of the approach.
Open Access
Towards Determining Wall Properties with Bistatic Radar
(Cranfield University, 2017-12-14 11:01) Elgy, James; Andre, Daniel; Morrow, Ivor; Finnis, Mark
Poster presented at the 2017 Defence and Security Doctoral Symposium.Remote sensing techniques to gather information about building structure and interiors are of significant interest for both military and civilian applications. Radar offers an attractive approach due its long-range, all-weather and non-destructive through-wall sensing nature. Radar however, is affected by the electrical properties of the medium the electromagnetic waves are passing through. For through-wall Synthetic Aperture Radar (SAR), this leads to a defocusing and a distortion of the resultant radar images due to the decrease in velocity and refraction of the radio waves. Compensation for this effect is possible if the properties of the medium are accounted for.This research contributes to the Remote Intelligence of Building Interiors (RIBI) project through use of multistatic measuring geometries and novel signal processing techniques to determine the thickness, refractive index and other electrical properties of walls, remotely, in both laboratory and realistic environments.We present experimental results, gathered at the Cranfield University Antennas and Ground-Based SAR (AGBSAR) laboratory to both validate our simulations and to illustrate the effectiveness of our proposed method as a means of addressing some of the fundamental issues with through-wall radar remote sensing.
Open Access
Volumetric interferometry for sparse 3D synthetic aperture radar with bistatic geometries
(Institution of Engineering and Technology (IET), 2023-06-25) Welsh, Richard; Andre, Daniel; Finnis, Mark
Synthetic Aperture Radar (SAR) renderings in 3D provide additional target information when compared to 2D by separating out features overlaid in height. However, the required 2D SAR aperture, when Nyquist sampled, necessitates large scanning times that would be impractical for most realistic collections. This research has developed a novel volumetric approach to sparse aperture 3D SAR imaging, that is applicable to bistatic SAR near-field geometries, a generalization of far-field cases. This approach is first demonstrated in simulation and then applied to a measured scene containing a model vehicle target, producing sub-Nyquist sampled 3D SAR renderings.