Modal analysis of vertical array receptions for the Heard Island Feasibility Test
Sperry, Brian J.
MetadataShow full item record
During the 1991 Heard Island Feasibility Test, a vertical hydrophone array deployed off Monterey, CA, recorded transmissions from a low-frequency acoustic source nearly 18,000 km away. By determining the modal structure of the received transmissions, it is possible to characterize the physics of such long range propagation. This thesis focuses on the determination of the modal, or vertical, structure of the signal. It was necessary to first develop a conditioning scheme to address several data quality issues, including very low signal levels (-15 dB SNR on a single channel), large transient spikes, and a limited set of operational channels. Very narrowband filtering was used to obtain a 25 dB increase in SNR. Doppler shifts for each transmission event were predicted from available parameters and were found to be within ±2 mHz of the measured shifts. The modal analysis employed two methods: comparing variations in signal energy with depth to the vertical extent of the modes, and fitting the data using a least squares modal decomposition. The least squares performance given a subsampled basis set of modes was studied and improved upon through the use of diagonal loading. Lack of array orientation data hindered the analysis, and least squares fitting was used to estimate the most likely orientation. The least squares analysis indicated the presence of modes at least up to mode 7, possibly higher. This is significant in that predictions prior to the experiment were that all but the lowest modes would be attenuated by boundary interactions along the path. Results from independent analyses of the same data also support the conclusion that the signal structure is quite complex.
Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and Woods Hole Oceanographic Institution May 1994
Showing items related by title, author, creator and subject.
Analysis of modal evolution caused by a weakly range-dependent seabed in shallow water and its application to inversion for geoacoustic properties Ohta, Kazuhiko (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1993-09)In a shallow water ocean environment, the range-dependent variation of the geoacoustic properties of the seabed is one of the crucial factors affecting sound propagation. Since the local modes of propagation depend on ...
Modal analysis of the range evolution of broadband wavefields in the North Pacific Ocean : low mode numbers Udovydchenkov, Ilya A.; Brown, Michael G.; Duda, Timothy F.; Mercer, James A.; Andrew, Rex K.; Worcester, Peter F.; Dzieciuch, Matthew A.; Howe, Bruce M.; Colosi, John A. (Acoustical Society of America, 2012-06)The results of mode-processing measurements of broadband acoustic wavefields made in the fall of 2004 as part of the Long-Range Ocean Acoustic Propagation Experiment (LOAPEX) in the eastern North Pacific Ocean are reported ...
Tracey, Brian H. (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1996-01)Acoustic propagation in the ocean can be strongly affected by small random variations in ocean properties, including rough surfaces and volume fluctuations in the ocean or seabed. Such inhomogeneities scatter part of the ...