Temporal coherence after multiple forward scattering through random three-dimensional inhomogeneities in an ocean waveguide.
An analytical expression is derived for the temporal coherence of an acoustic field after multiple forward scattering through random three-dimensional (3D) inhomogeneities in an ocean waveguide. This expression makes it possible to predict the coherence time scale of field fluctuations in ocean-acoustic measurements from knowledge of the oceanography. It is used to explain the time scale of acoustic field fluctuations observed at megameter ranges in various deep ocean-acoustic transmission experiments. It is shown that this time scale is nonlinearly related to the much longer coherence time scale of deep ocean internal waves through a multiple forward scattering process. It is also shown that 3D scattering effects become pronounced when the acoustic Fresnel width exceeds the cross-range coherence length of the deep ocean internal waves, which lead to frequency and range-dependent power losses in the forward field that may help to explain historic long range measurements.
Chen
Tianrun
T
Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Ratilal
Purnima
P
Makris
Nicholas C
NC
D000162:Acoustics; D003198:Computer Simulation; D009791:Oceanography / Q000379:methods*; D009792:Oceans and Seas; D012623:Seawater; D013016:Sound; D013997:Time Factors