Doctoral Degrees (Electrical and Electronic Engineering)

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Browsing Doctoral Degrees (Electrical and Electronic Engineering) by Subject "Airborne surveillance"

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    Aspects of small airborne passive millimetre-wave imaging systems
    (Stellenbosch : University of Stellenbosch, 2010-03) Smith, David Michael Patrick; Meyer, P.; University of Stellenbosch. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
    ENGLISH ABSTRACT: Passive millimetre-wave (PMMW) imaging is a technique that uses radiometers to detect thermal radiation emitted and reflected by metallic and non-metallic objects. While visual and infra-red emissions are attenuated by atmospheric constituents, PMMW emissions are transmitted, resulting in consistent contrast between different objects from day to night in clear weather and in low-visibility conditions to form images for a range of security and inclement weather applications. The use of a PMMW imaging system on a small unmanned aerial vehicle (UAV) offers extremely attractive possibilities for applications such as airborne surveillance for search and rescue operations, which are often hindered by inclement weather making visibility poor and endangering the rescuers as the search vehicle flies through the bad weather zone. The UAV would fly above the bad weather zone, with the PMMW imaging system detecting the thermal radiation emitted and reflected by objects in the MMW spectrum through the inclement weather. The 35GHz propagation window is chosen for the greater transmission through atmospheric constituents. The design of the PMMW imaging system is severely limited by the size of the UAV, particularly in the inability to incorporate any form of optical or mechanical scanning antenna. A possible solution is a long, thin antenna array fitted under the wings of the UAV. Such an antenna has a narrow, high gain, frequency-scanned beam along the plane perpendicular to the flight path, but a very broad beam along the plane of the flight path blurs the image, making it difficult to accurately determine the position of an object or to differentiate between objects situated along the plane of the flight path. This dissertation proposes a technique of image reconstruction based on the Kalman filter, a recursive filter that uses feedback control to estimate the state of a partially observed non-stationary stochastic process, to reconstruct an accurate image of the target area from such a detected signal. It is shown that given a simulated target area, populated with an arbitrary number of objects, the Kalman filter is able to successfully reconstruct the image using the measured antenna pattern to model the scanning process and reverse the blurring effect