Geometrical Evolution of Phase Gradient Autofocus for Navigation Correction Estimation

Abstract:
Synthetic Aperture Radar (SAR) is an active, coherent remote sensing method that allows the acquisition of highresolution images of the observed scene. To obtain fully focused and well-localized images, it is crucial to know platform position to within an accuracy of a fraction of wavelength. If this is not the case, the focusing process may result in severely blurred images. In this work, we present a low-complexity geometrical evolution of the well-known Phase Gradient Autofocus (PGA) algorithm for the estimation of trajectory corrections. The proposed algorithm addresses the strict constraint of traditional PGA regarding constant phase compensation for any point in the observed area, making it inapplicable in certain scenarios, such as low-altitude applications with strong space-varying phase errors. We test the algorithm using both numerical simulation and real-world data, demonstrating its feasibility and applicability to all SAR platforms.