Browsing by Author "Elgy, James"

Now showing 1 - 7 of 7
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    Bistatic 3D SAR for wall parameter extraction in cluttered environments
    (Institution of Engineering and Technology (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.
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    Bistatic SAR for Building Wall Material Characterisation
    (Cranfield University, 2020-07) Elgy, James; Andre, Daniel
    This 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 imagin
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    GBSAR-Proc
    (Cranfield University, 2019-08-22 15:56) Elgy, James
    The GBSAR-Proc Python package is designed to load and process data gathered from Cranfield University's ground based Synthetic Aperture Radar (SAR) system. Included in the package are a series of classes designed to manipulate raw data, process it into range profiles and finally use the Backprojection Algorithm to plot high quality near-field SAR images. In addition to the more common planar SAR images, there is functionality to both generate and plot volumetric SAR images, formed on either the CPU or GPU.
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    Non-Invasive Determination of Wall Structure and Material Using Synthetic Aperture Radar
    (Cranfield University, 2018-11-15 17:16) Elgy, James
    3MT presented at the 2018 Defence and Security Doctoral Symposium.Through-Wall remote sensing has become an area of great interest in both civilian and military sectors, with uses ranging from search and rescue to the assessment of the insulation used in building construction. Low frequency Synthetic Aperture Radar (SAR) is an attractive option due to its long-range, all-weather and non-destructive nature, with different radar modalities each providing useful information. Unfortunately, in a through-wall scenario, radar accuracy is inherently decreased due to the electrical properties of the wall material, leading to defocused and distorted images. Funded in part by Dstl, this research focuses on the remote determination of the thickness and refractive index of walls, through the use of different radar measuring geometries. In addition to providing useful auxiliary information, the knowledge of the wall properties can be used to improve the quality of through-wall SAR imagery and to address some of the fundamental limitations of the technology .
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    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.
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    Volumetric SAR near-field upsampling and basebanding
    (IET, 2020-03-03) Elgy, James; Andre, Daniel; Finnis, Mark V.
    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.
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    X Ray Eyes: Seeing Through Walls Using Radar
    (Cranfield University, 2018-11-15 10:39) Elgy, James
    Digital Image presented at the 2018 Defence and Security Doctoral Symposium.This image represents current research into ground-based applications of radar imaging in a through-wall context. Utilising different measurement geometries and signal processing, the aim is to gather and disseminate low-frequency synthetic aperture radar data to identify building structure and content. This image shows volumetric synthetic aperture radar data gathered in a multistatic modality, i.e. where there are two independent receiving antennas, both on the far side of the wall. This is superimposed onto a photograph of the same area, showing good agreement between the visual and radar images. For clarity, the point cloud has been segmented into different regions, each given a separate colour. Red represents the two metal barrels, blue shows the desk area whilst green represents the wall signature.