UBC Theses and Dissertations
Digital processing algorithms for bistatic Synthetic Aperture Radar data Neo, Yew Lam
The motivations for this thesis are the investigation of bistatic Synthetic Aperture Radar (SAR) image formation and the development of bistatic SAR algorithms to accommodate various bistatic SAR geometries. Traditional monostatic SAR algorithms based on frequency domain methods assume a single square root (a hyperbolic) range equation. In bistatic SAR data, the range history of a target has a Double Square Root (DSR) in the range equation as both the transmitter and receiver can assume different motion trajectories. Thus, monostatic algorithms are not able to focus bistatic SAR data. The key step to many frequency based algorithms is to find an analytical solution for the spectrum of a reference point target. No simple analytical solution exists for the bistatic case because of the DSR in the range equation. Several algorithms have been developed to overcome this difficulty. These algorithms are reviewed and analyzed in this thesis to compare their processing accuracies and the type of operations they require. A solution to the two-dimensional point target spectrum based on the reversion of a power series for the general bistatic case is presented in this thesis. The accuracy of this new point target spectrum is compared with existing analytical point target spectra. Using this spectrum result, a bistatic Range Doppler Algorithm (RDA) is developed to handle the azimuth-invariant, bistatic case. In addition, the algorithm is used to focus real bistatic data acquired with two X-band SAR systems from Forschungsgesellschaft für Angewandte Naturwissenschaften (FLAN), namely the Airborne Experimental Radar II (AER-II) and the Phased Array Multifunctional Imaging Radar (PAMIR). To handle azimuth-variant cases, the Non-Linear Chirp Scaling (NLCS) algorithm is used. The original NLCS algorithm is developed to focus only short-wavelength bistatic cases with one platform moving and imaging at broadside and the other stationary. It is found that the NLCS is able to cope with the general bistatic case since it is able to handle range and azimuth-variant signals. To exploit this processing capability, the algorithm is extended further to accommodate squinted and long-wavelength bistatic cases where both platforms have dissimilar velocities and flight paths slightly non-parallel.
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