Ship noise spectrum analysis based on HHT

Ship noise spectrum analysis by HHT is a new method and essential for underwater target recognition. In the process, the end swings and overshoots/undershoots exist during empirical mode decomposition. Analyzing the feature of the cubic spline interpolation and cubic Hermite polynomial interpolation, a new method was proposed which made use of cubic Hermite polynomial interpolation for envelopes fitting, and the ARMA process combined with period extraction for ending extension to improve the fitting result. Then, a non-stationary time series and two adjacent-frequency signals separation were used to test its efficiency. Finally, in ship noise analysis, we obtained the foundamental frequency and its frequency doubling components satisfactorily.