Three-dimensional reconstruction of underwater objects from a sequence of sonar images

This paper describes a method to estimate the three-dimensional aspects of underwater objects using a sequence of sonar images. The data are recorded by a sector scanning sonar, carried by an underwater vehicle which follows a circular track around the object. The sonar images are segmented into three kinds of regions : echo, shadow and background. The echo information corresponds to the signal back-scattered by the object while the shadow is due to the absence of back-scattering from behind the object. The remaining information composes the background. The reconstruction scheme processes the echo and shadow information separately. A two-dimensional elevation map is estimated from the shadow information and a two-dimensional reflection map is computed from the echoes. The final reconstruction merges these two maps