Measurements of the space–time–frequency distribution of the noise in the surf zone

The space–time–frequency distribution of the noise generated in the surf zone was measured in the SandyDuck’97 experiment during September and October 1997. The noise measurements were obtained on a 17-phone, 138-m, bottom-mounted, linear array located along a line perpendicular to the shore at a depth of one to three meters. Concurrent measurements of the location, size, and time evolution of the individual breaking waves directly above the array were made using a video camera mounted on a nearby tower. The measurements of the time history of the noise at individual phones along the array indicate that in regions of wave breaking, the noise contributions are broadband bursts, isolated in time with significant variations in level. A significant number of these broadband bursts exhibit a downward frequency sweep. Similarly, measurements of the time history of the noise observed along the array at selected frequencies show significant variations in both the range extent and the propagation speeds of the noise sources. The paper will present an interpretation of this variability in terms of the space–time distribution of the breaking waves obtained from the video measurements. [Work supported by ONR.]