Publications
Array processing techniques for broadband mode estimation
Abstract
Normal mode representations are useful in many aspects of underwater acoustics, e.g., modal acoustic tomography uses precise measurements of the travel time of broadband pulses to invert for environmental parameters. A thorough understanding of the resolution of mode estimators is crucial for tomographic applications. Typically, acoustic modes are used for describing and analyzing the temporal and spatial structure of narrowband signals. As source bandwidth increases, however, mode estimation algorithms can no longer ignore frequency variations of the modal wavenumbers, which result in temporal dispersion and frequency-dependent modeshapes. To address the issue, this study establishes an array processing framework for estimating the modal composition of broadband receptions. Within this framework, the time/frequency resolution tradeoffs inherent in the processing of modal pulse arrivals are explored. Specifically, the effects of modeshape frequency variations on standard modal beamformers are investigated. In addition to characterizing the performance of spatial filters for mode separation, this study considers the problem of designing receivers to compensate for the dispersion (pulse-spreading) introduced by the waveguide.
Techniques developed through theoretical work have been applied to data from the Acoustic Thermometry of Ocean Climate (ATOC) project. Some results of modal time series analysis for 1996 ATOC receptions are presented.
© 1997 Acoustical Society of America. This abstract may be downloaded for personal use only. Any other use requires the permission of the author and the Acoustical Society of America. The abstract appeared in the Journal of the Acoustical Society of America, vol. 101(5), pp. 3113-3114, May 1997 and may also be found on the JASA website.