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Figure 5
future Directions
We have concentrated here
on the internal wave field as
one of the “major players” in
determining Lcoh in shallow
water, but as we said at the
beginning, it is only one of
a number of shallow water
oceanography processes that
affect the overall coherence length. We still have a number left to treat: internal tides, eddies, linear internal waves, spice, bottom geo- acoustic properties and bathymetric scattering. These will be treated similarly to what we have done with nonlinear internal waves here, and so this paper hopefully gives a good representation of our work. An interesting question that will need to be answered when we get through the list is: what are the dominant effects? The overall coher- ence length measured (whether modal or otherwise) will be some sort of weighted average of all these effects, with the smallest (limit- ing) length of a strong process probably determining the result the most. We can’t linearly superpose Lcoh results, so some reasonable scheme for weighting will need to be devised.
Another useful direction for this work is to look at source/receiver motion through the ocean (feature model) medium. For sources and receivers that move quickly compared to the ocean features (gener- ally true, with the exception of surface waves), the ocean can be taken as “frozen” and useful results obtained quickly from the forms we have been considering.
Yet another major direction for the work is to look at other impor- tant acoustic quantities with this simple feature model approach. Of first order interest will be: the transmission loss (TL), the scintil- lation index (SI), and the mode coupling matrix (Cmn.) All of these, based on some preliminary work, should be amenable to this approach, and we look forward to completing these extensions in the future.
We will conclude with our thanks to a departed, but never-to-be-forgotten col- league, Bill Carey, for provid- ing us with yet another set of puzzles to solve. We hope he would be pleased by these few
pieces we have been able to place together so far.
Figure 5 : Visual look at the mode-by-mode coherence of the first four modes in SW06. Intensity on the L-array is plotted.
Acknowledgements
We thank ONR for their support of this work throughout the years. We also thank Allan Pierce for his critical reading of our paper. Thanks too to Art Newhall for his help with the figures. And again, we thank Bill Carey for his inspiration.
biosketches
Dr. James Lynch obtained his B.S. in Physics from Stevens Institute of Technology in 1972 and his Ph.D. in Physics from the University of Texas at Austin in 1978. He then worked for three years at the Applied Research Labo- ratories of the University of Texas at Austin (ARL/UT) from 1978 to 1981, after which
he joined the scientific staff at the Woods Hole Oceanographic Institution (WHOI). He has worked at WHOI since then, and cur- rently holds the position of Senior Scientist. His research specialty areas are ocean acoustics and acoustical oceanography. He also greatly enjoys occasional forays into physical oceanography, marine geology, and marine biology. Dr. Lynch is a Fellow of the Acoustical Society of America, a Fellow of IEEE, a former Editor-in-Chief of the IEEE Journal of Oceanic Engineering, and current Editor-in- Chief of the Journal of the Acoustical Society of America Express Letters. His hobbies include amateur astronomy and computer gaming.
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