Suppression of ship harmonic lines using the coherent onion peeler

The coherent onion peeler (COP) algorithm is derived by minimizing the error in the coherent subtraction of data from a single plane wave model. After the direction of the strongest interferer is known, a plane wave model is built to subtract most of the interference noise. If the strongest interferer is suppressed, COP can be applied to the second strongest interferer, and then to other interferers present. The COP solution has the FFTs form rather than the beam, so the residual FFTs can be beamformed using any beamforming algorithms after COP's process on hydrophone FFTs. In this paper, it is proposed that COP is used for suppressing ship harmonic lines so that a weaker target can be detected. The ship interferer harmonic lines are the main part of ship radiated noise at low frequency, which always hinders the detection of weak targets. In this paper, the basic principles and derivation of the COP algorithm for an equally spaced line array was given, and then a computer simulation was completed. COP was used to suppress the ship harmonic lines in the background noise field with Gaussian statistics. The result showed that COP reduced the harmonic lines by a large margin and the weak target was detected successfully. COP therefore shows great promise for incorporation in real sonar systems.