Nonstationarity analysis of line spectrum and range estimation by spectrum interference

The purpose of the research is to investigate the line spectrum nonstationarity of radiated noise produced by moving vessels, and to use the features to improve sonar detection performance and to realize the ranging function. The line spectrum nonstationarity comes from 3 aspects:instability of sound source, propagation path and relative movements of sound source and receiver. Several typical patterns of line spectrum are summarized after the time-frequency analysis of a large amount of samples. Different patterns have different processing methods, taking a long time-integral for a stable line pattern, using Dopplerlet for a varying line pattern by relative movements of sound source and receiver, using Kalman filter for intermissive line pattern. A theory analysis is made for a phenomenon of "line group" which is bell shaped, and the spectrum interference between direct path sound and reflected sound is revealed. One kind of ranging method that employs the superimposed interference pattern is utilized to find moving vessel range. Finally the range and depth estimation of a moving vessel is given using this method.