Synthetic Aperture Sonar Technology Research

Aperture synthesis sonar, as its name implies, synthesizes 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. To increase its feasibility will be an important aspect in our sonar technology development.The thesis reviews the theory which is the basis of synthetic aperture processing and introduces five algorithms of image reconstruction: the coherent addition provides a good opportunity for the real time SAS; the envelope processing can work when sonar echo returns lack phase coherence; the I-Q processing can reduce the sampling rate; the broadband and CTFM processing are both aimed to increase the SAS mapping rate. The restrictions on the under water applications of the synthetic aperture technique are introduced followed by discussions of an autofocus technique that compensates the motion errors of the platform and the phase differential processing that has been developed to be less sensitive to media turbulence and transducer motion errors. The simulations concerned are also presented.