A low-order autofocus algorithm

Synthetic aperture processing critically depends on the coherent ping-to-ping nature of the collected data. Phase errors are introduced when the sonar path deviates from a straight line and when the sound speed in the volume of interest is not perfectly constant. Much effort has been spent measuring and estimating corrections to the sonar motion. Phase errors due to inhomogeneous sound speeds are commonly corrected using autofocus algorithms. This paper introduces an autofocus algorithm that constructs an effective correction vector based on a low-order sine series approximation.