On Correlating Sonar Images

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.