Modifying Range-Doppler geometry frameworks to process Spotlight SAR imagery in Polar Format

We present a simple method to enable processing of Spotlight Synthetic Aperture Radar (SAR) imagery distributed in Polar Format (PFA) using standard Range-Doppler (RDA) geometry algorithms. Our approach is applicable to PFA SAR images characterized by a constant value of the Center of Aperture (COA) time. We present simplified expressions for forward (image-to-ground) and inverse (ground-to-image) geometry mapping using Sensor Independent Complex Data (SICD) conventions. We discuss simple changes needed to current open source SAR software that implement Range-Doppler algorithms, to enable support within them for Spotlight data distributed in SICD format. We include a proof-of-concept script that utilizes the Python packages sarpy and isce3 to demonstrate the correctness of the proposed approach.