Abstract

Synthetic aperture sonar (SAS) is an underwater imaging technology whose image accuracy depends on the motion stability of the carrier platform. Nevertheless, underwater platforms inevitably experience unwanted movements in all six degrees of freedom, which result in phase errors and image quality degradation. So far, no comparative study has evaluated the effect of each of these motions on phase error and image quality, and most recent research has merely focused on geometric compensation of motion errors, overlooking quantitative assessment of their impact on image quality.

In this research, the effects of sinusoidal unwanted platform motions in six degrees of freedom—including surge, sway, and heave displacements as well as rotational motions: roll, pitch, and yaw—have been numerically simulated and compared. To this end, the phase error induced by platform motion was modeled, and by calculating the RMSE, PSNR, PSLR, and ISLR metrics under various conditions, the system’s sensitivity to increasing error amplitude was assessed. Simulation results show that among translational motions, vertical displacement (heave) has the most detrimental impact: displacements exceeding 0.1 m cause a severe drop in image quality, with PSNR falling below 20 dB and RMSE rising above 0.1 m. sway displacement above about 0.5 m also rapidly reduces quality, while surge displacement has the least effect, with noticeable degradation occurring only at very large errors. Among rotational motions, rotation about the yaw has the greatest destructive effect, with deviations beyond 5° leading to severe image degradation, while roll remains the most stable axis, and the image remains nearly intact for deviations up to 5°.

Consequently, controlling and stabilizing vertical, lateral, and yaw motions of the carrier platform are essential in the design of synthetic aperture sonar systems to ensure stable and high-quality imaging.