3D reconstruction of small underwater objects using high-resolution sonar data

A high-resolution, very compact acoustic lens sonar was used to investigate how well small underwater objects can be reconstructed in 3D. The purpose was to develop an acoustic snapshot approaching photographic quality in turbid water where cameras and lens are ineffective. In-water experiments have provided data from an 8-by-8 array of acoustical beams with 1.5 degree conical resolution. Algorithms have been developed to interpolate the conical grid onto a grid. Once gridded, a volume rendering algorithm was applied to produce a full 3D rendering of the object. The sensitivity of this process to different gridding algorithms is evaluated. It is shown that objects can be quantified in size quite precisely. The degree to which shape can be extracted and small details made visible is discussed. The authors also consider how well the reconstruction can be improved by using multiple passes over the object. Registration algorithms are presented, and it is shown that the alignment process can be done with enough accuracy to improve the image and provide greater detail about the object