Time-frequency analysis of acoustic transients

We apply time-frequency analysis to various acoustic transients. Estimates of the conditional mean frequency and the conditional bandwidth exhibit characteristic trends for different transients. This information may be helpful in distinguishing between different classes of transients, and in understanding the underlying mechanisms generating the transient. 1. INTRODUCTION One of the primary means for locating and identifying submerged submarines is via the detection and analysis of acoustic emissions from the submarine. Spectral analysis has been particularly effective for identifying so called steady-state acoustic sounds, such as those associated with propeller noise. This analysis has been beneficial to the design of " quiet " submarines: silencing efforts, such as hull isolation and damping, have resulted in significant reduction in the radiation of steady-state acoustic energy from modern submarines. However, as the level of radiated steady-state or stationary energy has been reduced, the level of radiated energy associated with transient events, such as hatch slams and control surface movements, has not been significantly reduced. Consequently, transients have become a focus for detecting submerged submarines. Because transients are potentially a primary source for detecting (and possibly identifying) submarines , it is becoming increasingly important to identify the threat they pose to detection by enemy ships. If US submarines are to acquire the same level of " quiet character " for transients as they currently have for steady-state acoustic emissions, a thorough understanding of the spectral structure and character