Image quality improvement of underwater synthetic aperture ultrasonic holography by deconvolution of spatial response of transducers

This paper studies the effect of transducer spatial response on the measured underwater ultrasonic pressure field, and eliminates this effect by using of the deconvolution technique to improve the image resolution and modulation transfer function (MTF) of underwater synthetic aperture ultrasonic holography (SAUH) imaging systems, in which resolution is usually limited by the spatial size of transducers. Plane non-focused ultrasonic transducers are adopted in this paper. To deconvolve the effect of transducer spatial response on SAUH images, we utilize pseudo-inverse filters derived from two types of transducer response. The first one is of single-transducer and the other is of combined-two-transducers obtained by using of the technique named spatial filtered incoherent summation (SFIS). Both numerical simulation and experiment are applied to verify the capability of deconvolution process. Results show, the image resolution can be apparently improved by deconvolving the transducer finite size effect, and the low signal-to-noise region of spatial-frequency response of transducers can be compensated by the SFIS technique, and more spatial frequency information with better resolution and MTF (modulation transfer function) will be restored.