On Correlating Sonar Images

Abstract

This paper demonstrates that sonar images correlate badly because target geometry and image fringes correlate in different coordinate systems. It is shown that if the receiver is a line array, all point objects have the same image in a coordinate system with axes of range and the sine of target bearing (the (r, s) coordinate system). Results from an ocean experiment are presented. The ocean experiment shows that after a simple translation, the correlation coefficient between Cartesian images of a radar reflector drop to zero, while the correlation coefficient between images of the same radar reflector in an (r, s) coordinate system hover around 0.9.