Synthetic Aperture Radar Single Look Complex (SAR SLC) Image Quality Assessment Using the Minimum-Entropy Refocusing Velocity Parameter

This paper proposes two quantitative evaluation criteria for assessing the quality of synthetic aperture radar (SAR) single look complex (SLC) imagery using the minimum entropy refocusing velocity (MERV) derived during the refocusing process. The method aims to objectively quantify residual phase errors—caused by inaccurate satellite velocity estimates that induce azimuthal defocus—more rigorously than existing metrics. The first criterion, a standardized metric (Z-score), is a dimensionless score computed by dividing the MERV error by a scene-adaptive horizontal reference distance derived from the entropy–velocity curve. This metric enables consistent comparison of focus quality across all SLC products, regardless of scene content or system operating conditions. The second criterion, a quadratic phase error (QPE) pass/fail test, determines whether the QPE computed from MERV lies within a negligible-defocus threshold (π/4) and serves as a complementary check to the MERV-based evaluation. Applied to Sentinel-1A/C data, the approach confirms scene-agnostic applicability, and the combined MERV-based criteria provide a consistent and reproducible assessment of azimuth focus quality in SAR imagery.