Frequency analysis of broadband acoustic signals propagating through nonlinear internal waves

Nonlinear internal waves along the ocean thermocline are known to affect modal compositions and other properties of acoustic signals. Such nonlinear waves were observed during the SWARM 95 Orthogonal Propagation Experiment, where extensive data were collected from two broadband sources. One source was a 30‐s linear frequency modulated sweep signal, and the other was a 0.1‐s airgun shot. Both sources were repeated every minute and received by two vertical linear arrays several kilometers away. Sound speed profiles were measured near the source and the receiver arrays simultaneously. The influences of internal waves on the broadband frequency behavior of received and simulated signals are described. Features of energy spectral density and of transmission loss versus frequency plots are used to detect resonant frequencies where anomalous loss occurs. A time‐frequency analysis of received signals at several ranges is performed to determine modal propagation characteristics, including modal transitions of the ...