SAR Imaging Using the Back Projection Algorithm

Core Concept and Application of the Back Projection Algorithm in SAR Imaging

Synthetic Aperture Radar (SAR) imaging is a technique for acquiring high-resolution terrain images via radar systems, with the Back Projection (BP) algorithm serving as a classical time-domain processing method. Unlike frequency-domain algorithms, the BP algorithm directly utilizes time-domain echo data received by the radar for imaging, offering advantages such as high tolerance to motion errors and adaptability to irregular flight trajectories.

The BP algorithm reconstructs images by back-projecting echo data received at each radar position onto every pixel in the imaging area. Specifically, the algorithm calculates the two-way propagation delay between the radar and each pixel, then coherently integrates the echo signal corresponding to that delay into the pixel value. Although this pixel-by-pixel approach is computationally intensive, it precisely compensates for phase errors induced by platform motion, making it particularly suitable for airborne or UAV-based SAR systems. In code implementation, this involves nested loops over radar positions and pixels, with delay calculation using Euclidean distance and interpolation for non-integer delay indices.

Practical applications of the BP algorithm require consideration of radar beam geometry and time-delay calibration for signal propagation. By strategically partitioning the imaging area and optimizing projection paths (e.g., through parallel computing or GPU acceleration), computational efficiency can be improved while maintaining image quality. Key implementation aspects include range migration compensation and phase preservation during coherent summation. The algorithm demonstrates strong adaptability in military reconnaissance, topographic mapping, and other fields, establishing itself as a vital tool for SAR imaging in complex scenarios.