Gain and Phase Variations in Holographic Acoustic Imaging Systems

Abstract

The effect of random gain and phase errors in the hydrophones and associated amplifiers in a uniformly-filled square array of a holographic acoustic imaging system is theoretically analyzed. Temporal noise introduced by the amplifiers is also considered. The contrast of the image reconstructed from the holographic information is shown to depend on the statistics of the array, on the dynamic range of the amplifiers, and on the intensity distribution of the target. It is also shown that image contrast depends on field-of-view location when the width of the sensing elements in the array is an appreciable fraction of the separation of the elements. A method of compensating for known gain and phase variations is presented. The theory is used to evaluate the performance of some existing systems.