Focused beamforming for underwater imaging: depth of field and range resolution optimization

Addresses two problems that characterize the formation of underwater acoustic images (3D maps) by focused beamforming. When usual parameters are chosen to achieve an accurate lateral resolution, the depth of field provided by focused beamforming is insufficient to build a flexible imaging system. Moreover, the accuracy of range determination is directly proportional to the signal bandwidth. The authors propose an evaluation methodology, namely, confidence measure, which, is calculated on the beam signal profile, and permits one to determine the exact position of an attenuated pulse in time by a comparison with an expected model of the beam signal. The confidence measure makes it possible to improve the precision of range determination and to generate an algorithm that, without any a priori knowledge of a scene, succeeds in focusing each beam signal correctly. Finally, they compare, in terms of image quality, sensitivity to noise, and processing time, the results obtained by the proposed algorithm with those obtained by fixed and dynamic focalizations