Correction of distributed phase aberrations caused by propagation-speed and array-pitch errors

When an incorrectly assumed array pitch or propagation speed is used to form an image, phase aberrations are generated even in a homogeneous medium, and they are distributed. That is, at different image points the phase aberration profiles are different. Even though array pitch and propagation speed are usually known quite accurately, it is important and interesting to test whether a phase aberration correction algorithm is capable of correcting distributed phase aberrations caused by incorrect array pitch and propagation speed values. It was demonstrated that the Near Field Signal Redundancy (NFSR) algorithm is able to correct these kinds of phase aberrations with data from a linear array. However, only a single phase-aberration profile was measured and the image quality after correction was only improved in a small region. In this paper we present new results from a phased array where multiple phase aberration profiles have been measured and the whole image has been corrected. These results have further demonstrated that the NFSR algorithm is capable of correcting distributed phase aberrations caused by array pitch and propagation speed errors.