Opportunistic radar imaging using a multichannel receiver

Bistatic Synthetic Aperture Radars have a physically separated transmitter and receiver where one or both are moving. Besides the advantages of reduced procurement and maintenance costs, the receiving system can sense passively while remaining covert which offers obvious tactical advantages. In this work, spaceborne monostatic SARs are used as emitters of opportunity with a stationary ground-based receiver. The imaging mode of SAR systems over land is usually a wide-swath mode such as ScanSAR or TOPSAR in which the antenna scans the area of interest in range to image a larger swath at the expense of degraded cross-range resolution compared to the conventional stripmap mode. In the bistatic geometry considered here, the signals from the sidelobes of the scanning beams illuminating the adjacent sub-swath are exploited to produce images with high cross-range resolution from data obtained from a SAR system operating in wide-swath mode. To achieve this, the SAR inverse problem is rigorously formulated and solved using a Maximum A Posteriori estimation method providing enhanced cross-range resolution compared to that obtained by classical burst-mode SAR processing. This dramatically increases the number of useful images that can be produced using emitters of opportunity. Signals from any radar satellite in the receiving band of the receiver can be used, thus further decreasing the revisit time of the area of interest. As a comparison, a compressive sensing-based method is critically analysed and proves more sensitive to off-grid targets and only suited to sparse scene. The novel SAR imaging method is demonstrated using simulated data and real measurements from C-band satellites such as RADARSAT-2 and ESA’s satellites ERS-2, ENVISAT and Sentinel-1A. In addition, this thesis analyses the main technological issues in bistatic SAR such as the azimuth-variant characteristic of bistatic data and the effect of imperfect synchronisation between the non-cooperative transmitter and the receiver

Low cost passive radar through software defined radio

Passive radars utilise existing terrestrial radio signals, such as those produced by radio or television stations, to track objects within their range. This project aims to determine the suitability of low cost USB TV tuners as hardware receivers for a Software Defined Radio (SDR) based passive radar receiver. Subsequently determining its effectiveness in producing inverse synthetic aperture radar images using data collected from Digital Television signals. Since the initial identification of passive radar, Militaries the world over have been using it as a part of electronic warfare. The evolution of SDR has enabled greater access to the technologies required to implement passive radar, with the greatest limitation being the cost of the required hardware. The availability of low cost hardware was therefore investigated to determine its suitability and subsequently the availability of passive radar to a wider audience. Research was conducted into the available SDR receivers, and comparison of specifications was made against the low cost receiver used in the project. A functional hardware platform based around the Realtek RTL2832U chipset has been developed to determine its suitability as a low cost receiver verifying its ability to coherently receive radio signals for target identification. A complex ambiguity function was implemented to interpret sampled data windows, with the output of these windows to be compared to the requirements for an inverse synthetic aperture radar input, thus determining the suitability of the device. Interpretation of the received data has identified that although the hardware is capable, a real time implementation of data processing is not yet possible, impeding the ability to determine the suitability of the receiver as an inverse synthetic aperture receiver. The results of testing show that the hardware is capable of receiving and producing radar images, however due to the bandwidth of DVB-T signals , and the bandwidth limitations inherent in RTL-SDR dongles, they have proven not to be suitable for DVB-T based inverse synthetic aperture radar receivers

Bistatic SAR data acquisition and processing using SABRINA-X, with TerraSAR-X as the opportunity transmitter

This thesis investigates the acquisition and processing of Bistatic SAR data using SABRINA-X, and with TerraSAR-X as the transmitter of opportunity. SABRINA-X is an X-band receiver system that has been recently designed at the UPC Remote-Sensing Laboratory, while TerraSARX is a German satellite for SAR-based active remote-sensing. Prior to the particular case of acquiring TerraSAR-X signals, the hardware aspects of SABRINAX have been investigated further, and improved as necessary (or suggested for up-gradation in future). Two successful data acquisitions have been carried out, to obtain bistatic SAR images of the Barcelona harbor, with the receiver set-up at the close-by Montjuïc hill. Each acquisition campaign necessitated an accurate prediction of the satellite overpass time and precise orientation of the antennas to acquire the direct signal from the satellite and the backscattered signals off the viewed terrain. The thesis also investigates the characteristics of the acquired signals, which is critical as regards the subsequent processing for imaging and interferometric applications. The hardware limitations, combined with ‘off-nominal’ transmissions of the satellite, necessitate improved range processing of the acquired signals. The thesis expounds the possible range compression techniques, and suggests ways for improved compression, thereby improving the quality of the subsequently processed images

Wide-Angle Multistatic Synthetic Aperture Radar: Focused Image Formation and Aliasing Artifact Mitigation

Traditional monostatic Synthetic Aperture Radar (SAR) platforms force the user to choose between two image types: larger, low resolution images or smaller, high resolution images. Switching to a Wide-Angle Multistatic Synthetic Aperture Radar (WAM-SAR) approach allows formation of large high-resolution images. Unfortunately, WAM-SAR suffers from two significant implementation problems. First, wavefront curvature effects, non-linear flight paths, and warped ground planes lead to image defocusing with traditional SAR processing methods. A new 3-D monostatic/bistatic image formation routine solves the defocusing problem, correcting for all relevant wide-angle effects. Inverse SAR (ISAR) imagery from a Radar Cross Section (RCS) chamber validates this approach. The second implementation problem stems from the large Doppler spread in the wide-angle scene, leading to severe aliasing problems. This research effort develops a new anti-aliasing technique using randomized Stepped-Frequency (SF) waveforms to form Doppler filter nulls coinciding with aliasing artifact locations. Both simulation and laboratory results demonstrate effective performance, eliminating more than 99% of the aliased energy

Bistatic SAR data acquisition and processing using SABRINA-X, with TerraSAR-X as the opportunity transmitter

This thesis investigates the acquisition and processing of Bistatic SAR data using SABRINA-X, and with TerraSAR-X as the transmitter of opportunity. SABRINA-X is an X-band receiver system that has been recently designed at the UPC Remote-Sensing Laboratory, while TerraSARX is a German satellite for SAR-based active remote-sensing. Prior to the particular case of acquiring TerraSAR-X signals, the hardware aspects of SABRINAX have been investigated further, and improved as necessary (or suggested for up-gradation in future). Two successful data acquisitions have been carried out, to obtain bistatic SAR images of the Barcelona harbor, with the receiver set-up at the close-by Montjuïc hill. Each acquisition campaign necessitated an accurate prediction of the satellite overpass time and precise orientation of the antennas to acquire the direct signal from the satellite and the backscattered signals off the viewed terrain. The thesis also investigates the characteristics of the acquired signals, which is critical as regards the subsequent processing for imaging and interferometric applications. The hardware limitations, combined with ‘off-nominal’ transmissions of the satellite, necessitate improved range processing of the acquired signals. The thesis expounds the possible range compression techniques, and suggests ways for improved compression, thereby improving the quality of the subsequently processed images

Air Force Institute of Technology Research Report 2001

This report summarizes the research activities of the Air Force Institute of Technology’s Graduate School of Engineering and Management. It describes research interests and faculty expertise; lists student theses/dissertations; identifies research sponsors and contributions; and outlines the procedures for contacting the school. Included in the report are: faculty publications, conference presentations, consultations, and funded research projects. Research was conducted in the areas of Aeronautical and Astronautical Engineering, Electrical Engineering and Electro-Optics, Computer Engineering and Computer Science, Systems and Engineering Management, Operational Sciences, and Engineering Physics

Exploring bistatic scattering modeling for land surface applications using radio spectrum recycling in the Signal of Opportunity Coherent Bistatic Simulator

The potential for high spatio-temporal resolution microwave measurements has urged the adoption of the signals of opportunity (SoOp) passive radar technique for use in remote sensing. Recent trends in particular target highly complex remote sensing problems such as root-zone soil moisture and snow water equivalent. This dissertation explores the continued open-sourcing of the SoOp coherent bistatic scattering model (SCoBi) and its use in soil moisture sensing applications. Starting from ground-based applications, the feasibility of root-zone soil moisture remote sensing is assessed using available SoOp resources below L-band. A modularized, spaceborne model is then developed to simulate land-surface scattering and delay-Doppler maps over the available spectrum of SoOp resources. The simulation tools are intended to provide insights for future spaceborne modeling pursuits