Three-dimensional underwater imaging method - synthetic aperture image holography using an acoustic lens

This paper describes the three-dimensional underwater imaging method of "Synthetic Aperture Image Holography" which utlizes an acoustic lens and synthetic aperture sonar techniques. The imaging procedure is as follows : (1) a transmitter in the transmitting array projects pulsed ultrasound to the target, (2)the reflected ultrasound from the target is then focused by the acoustic lens, (3) the time series signals of the focused image are detected by the receiving array, (4) multiple images are obtained by using transmitters at different positions in the array and by repeating steps 1 though 3, and (5) the final three-dimensional image is calculated by synthesizing all of these images together. A method analysis reveals that synthetic aperture techniques increase the system\´s resolution over the normal resolution limit of the lens itself. It also shows that the acoustic lens reduces the amount of calculations needed to obtain the image because it does part of the calculations physically. A three-dimensional image is obtained by the experiments. Lateral and range resolutions obtained are nearly equal to theoretical ones.