Calibrated Synthetic Aperture Sonar (SAS) data can provide monostatic backscattering strength measurements as a function of grazing angle at high resolution. Motivated by an interest in obtaining invariant metrics from vehicle based sonar acquisition systems, an end-to-end processing methodology for recovering calibrated scattering cross section levels from seafloor swaths is presented. Calibrated SAS beamforming software developed for this work was based on the narrowband sonar equation and a delay-and-sum beamformer. Modern SAS processing techniques such as redundant phase center micronavigation, and an autofocus algorithm to estimate sound speed, were employed in the beamforming stage. Data from overlapping sections of seafloor acquired in the Gulf of Mexico during 2012 provide the basis for analysis of comparative scattering results, which are examined in an effort to demonstrate adherence to established acoustic principles.