Fast Back Projection Algorithm for Bi-Static SAR Using Polar Coordinates

Sammanfattning: Synthetic Aperture Radar (SAR) plays a significant role in geophysical studies and remote sensing applications. SAR inherits the benefits of imaging RADAR over the other optical sensors such as working in all weather conditions and working independently of sunlight. In addition to these benefits SAR generates a finer resolution 2-D image compared to conventional (real) aperture radar. Due to the sole merits of Ultrawideband-Ultrawidebeam (UWB) Bistatic SAR, this thesis introduces and analyzes a fast time domain algorithm for its image formation. This algorithm inherits the advantages of time-domain algorithms over frequency domain ones. It divides the full synthetic aperture into subapertures. Each subaperture generates a polar grid image. The key point is that the subaperture polar images have very low resolution in cross range (the angular direction); this means that they can be calculated on a pixel grid that is coarse in the angular direction. The final image is obtained by combining all subaperture polar images after converting them to the final high-resolution Cartesian image, in this conversion interpolation is used. Since the subaperture images contain far fewer pixels in cross range than the final image, far fewer operations are required to be executed as compared to Global Backprojection GBP. Due to using the polar grid, the proposed algorithm is named Bistatic Polar-FBP (Bi-PFBP). It is found that although for N×N scene image with N aperture positions the Bi-PFBP computational load is less by approximately a factor of √N as compared to GBP, the image quality generated by each one of them is almost the same.