ACOUSTIC NOISE INTERFEROMETRY

Acoustic noise interferometry uses long time series recordings of ambient and shipping noise, which are concurrently captured at two locations, to measure the acoustic Green’s function. With this technique, each hydrophone becomes a virtual acoustic transceiver—a combination of a source and a receiver—which can be used for passive acoustic remote sensing of the ocean. Compared to active techniques, passive remote sensing greatly reduces costs and allows for undetected, surreptitious monitoring of acoustic non-reciprocity, a sensitive measure of the velocity of oceanic currents. Using data obtained in the 2012 Florida Straits Noise Interferometry Experiment, this work investigated the feasibility of retrieval of the depth-dependence of the current velocity from the passively measured non-reciprocity of normal mode travel times in a shallow-water waveguide. It was found that measurements of the current-induced non-reciprocity of normal mode group speeds with errors up to 0.2 m/s will allow for inversion of the vertical current velocity profile with oceanographically relevant vertical resolution and accuracy. Additionally, passive measurements of acoustic non-reciprocity at frequencies below 80 Hz at ranges of about 50 times the ocean depth are sufficient for retrieval of the current velocity profile in shallow water. Thus, the technique investigated in the thesis can now be applied to field data, like those acquired in previous measurements in the Florida Straits.National Science FoundationLieutenant, United States NavyApproved for public release. distribution is unlimite