Doppler-only synthetic aperture radar
Chua, Cheng Lock Charles.
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SAR has traditionally been performed using high-range resolution data. This thesis is a proof-of-concept that the imaging process can be performed using high-doppler resolution data. The system requires a simple continuous wave transmitter, and the signal returns are confined to a narrow band. High-doppler resolution data is collected along an isodoppler line for different perspectives of the target. This data, a sinogram, is equivalent to taking the Radon transform of the target. The Fourier transform of the sinogram from each perspective (at an angle eÌ ) gives a slice of the two-dimensional transform subtending an angle eÌ with the axis, with equally distributed points along the line. This results in a higher density of points near the centre. Some form of weighting is necessary. This weighting is part of the Filtered Backprojection algorithm to determine the Inverse Radon transform of the sinogram. The backprojection portion is a simple redistribution of data back along the original projection line. Images were modeled by delta functions to test the above algorithm. The main points noted were that the reconstructed image was a scaled version of the original image, and that the quality of the image improved when more perspectives of the target were taken.
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