Study of aperture area reduction and resolution improvement of underwater ultrasonic imaging system

This paper describes an imaging method to reduce the aperture area while improving the cross-range resolution by using a cylindrical aperture combined with a digital signal processing technique called the "post-focusing" for the C-scope underwater MSAUIS (monostatic synthetic aperture ultrasonic imaging system). Both theoretical and experimental studies are conducted. This paper demonstrates that the conventional synthetic aperture (SA) processing is a simplified case of the post-focusing when the transducer is idealized as a point-like one. A non-focused transducer is adopted in the experiments, and the monostatic point reflector spreading function (MPSF) of transducer is obtained by performing the same experimental procedure to a point-like reflector. Results show, the MPSF of transducer is a crucial blurring factor affecting the image resolution of the underwater MSAUIS, and the post-focusing method is better than the conventional SA processing for cross-range resolution improvement. The synthetic cylindrical aperture can form a larger illuminating area than the SPA of the same aperture area.