1. A method for detecting correlation between sonar images, comprising the steps of: correlating a plurality of coherent sonar images to obtain a correlation image, wherein said correlation image comprises a matrix showing correlation coefficients vs. at least one of spatial translation and rotations; obtaining a mean of absolute values of correlation coefficients in said correlation image; determining a Rayleigh parameter from said mean; determining a threshold value based on a desired false detection probability; and registering a detection if a peak one of said correlation coefficients exceeds a product of said threshold and said Rayleigh parameter.