Creating synthetic aperture images using experimental and simulated backscattering of solid elastic cubes

To study aspect and material dependent backscattering of objects, we used cubes as their geometry has distinct exposure points for different backscattering mechanisms. We insonified two solid cubes, one brass and the other steel, in underwater tank scale experiments, measuring their backscattering using circular, linear, and cylindrical synthetic aperture sonar. The right angles of the edges allow for enhanced backscattering by Rayleigh waves, which couple in at material-specific angles, since the waves are retroreflected by the cube’s edges [K. Gipson and P. L. Marston, J. Acoust. Soc. Am. 105, 700-710 (1998)]. In concert with the experiments, we model the backscattering from our cubes using Kirchhoff-Integration based simulations. The simulation isolates the specular responses, simplifying the complex responses from the cube’s geometry and allowing us to identify specific effects, such as splitting from the corner reflections of a cube when its top ridge is tilted. Using Fourier based back-projection algorithms, we reconstructed target images from both the experimental and simulation results. Three dimensional images were also recreated from the cylindrical data. Using a combination of experimental and simulation results, we identified aspect dependent mechanisms. [Work supported by ONR.]