A study on a synthetic aperture sonar
Aperture synthesis, as its name implies, synthesises an aperture by storing successive echoes obtained from a moving platform and by processing the results as if they had been obtained from a multi-element array enables a high azimuth resolution to be obtained from a physically small array. The technique has been highly successful in radio astronomy, and in both satellite and aircraft borne radar. However the use of this technique has been very limited in the sonar environment mainly because of difficulties of maintaining a stable track under water and problems of under-sampling of the aperture arising from the relatively slow velocity of acoustic waves in water. The thesis describes a study of the application of the synthetic aperture technique to sonar, highlighting some of these difficulties and possible means of overcoming them. A study has also been made the application of the bathymetric technique, a technique for measuring the height of objects on the sea bed, to synthetic aperture sonar. In addition to the theoretical work and computer simulation, an experimental system has been built in a water tank measuring some 9m by 5m by 2m deep in order to test a number of the algorithms and some good results have been obtained.