Quadratic phase coupling analysis of passive sonar data using biphase techniques

In this work we report on the application of a higher order statistics based method that can be used to improve passive signature estimation over the conventional bispectrum methods. The method employs the biphase for extraction of frequency triplets with possible quadratic phase coupling. We demonstrate the method using data recorded by bottom mounted hydrophones during a sea trial in the Baltic Sea with a small fiberglass motor boat as a target. Several frequency pairs are shown to exist for which, according to the biphase test, there is significant quadratic phase coupling. This information can be useful to form complementary features for passive signature classification.