Investigation of an unusual noise phenomenon with horizontal and vertical hydrophone array data and three‐dimensional propagation modeling.

Abstract

Acoustic data from an experiment conducted during Shallow Water 2006 (SW06) showed an unexplained broadband noise phenomenon. While the R/V Knorr towed a J‐15 acoustic source, which emitted a 93 Hz continuous‐wave signal, the R/V Endeavor performed Scanfish measurements in the vicinity to characterize internal wave phenomena. The WHOI Shark horizontal and vertical hydrophone array detected the 93 Hz signal, but eventually the signal was overpowered by broadband low‐frequency noise. The broadband noise may be associated with either research vessel but is uncharacteristically intense given that both vessels were greater than 25 km away from the Shark array. The complex acoustic environment due to the shelfbreak front, an internal wave packet, and the bathymetry of the continental shelf may have caused ducting of the noise field. Both three‐dimensional acoustic modeling and array processing techniques will be used to characterize the unexplained noise levels. In situ data from temperature sensors and Scanfish measurements provide environmental information needed to accurately model the sound speed field. These methods can also be applied to other SW06 experiments that were tailored to investigate the role of internal waves in acoustic propagation—such as those carried out on the R/V Sharp. [Work sponsored by the Office of Naval Research.]