Fluctuations, Coherence and Predictability of Long Range Shallow Water Propagation in the Straits of Florida
1998
DeFerrari, Harry | Nguyen, Hien | Williams, Neil J.
See also ADM002252. Sponsored in part by ONR grant N00014-97-1-0373.
Show more [+] Less [-]Understanding long range acoustic propagation in shallow water. The coherence and predictability of long-range shallow water propagation deteriorates with higher frequency and longer range of propagation. We seek to understand the randomizing effect of fluctuations in bathymetry, sound speed and the geo-acoustic properties of the bottom. Usually, a propagating sound field is randomized after tens of kilometers of transmission but occasionally, stable and coherent signals are observed at much longer range (Monjo et al, 1997). We seek to explore these islands of coherence in a sea of chaos. Most shallow water experiments of the past focused on the fundamental problem of low frequency and short-range propagation resulting in a few acoustic modes. Mode theoretical approaches are used to interpret observations. We seek to expand the scope of observations to cover a broad band of frequencies 100 to 3200 Hz. and longer ranges of transmission with hundreds of modes. We hypothesize that wave-guide effects can produce phase-stationary summations of many modes in a way that will greatly enhance coherence under some conditions.
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