Analysis of Internal Wave Induced Mode Coupling Effects on the 1995 SWARM Experiment Acoustic Transmissions
As part of the Shallow Water Acoustics in a Random Medium (SWARM) experiment , a sixteen element WHOI vertical line array (WVLA) was moored in 70 meters of water off the New Jersey coast. This array was sampled at 1395 Hz or higher for the seven days it was deployed. Tomography sources with carrier frequencies of 224 and 400 Hz were moored about 32 km shoreward, such that the acoustic path was anti-parallel to the primary propagation direction for shelf generated internal wave solitons. Two models for the propagation of normal modes through a 2-D waveguide with solitary internal wave (soliton) scattering included are developed to help in understanding the very complicated mode arrivals seen at the WVLA. The simplest model uses the Preisig and Duda  sharp interface approximation for solitons, allowing for rapid analysis of the effects of various numbers of solitons on mode arrival statistics. The second model, using SWARM thermistor string data to simulate the actual SWARM waveguides, is more realistic, but much slower. The analysis of the actual WVLA data yields spread, bias, wander, and intensity fluctuation signals that are modulated at tidal frequencies. The signals are consistent with predicted relationships to the internal wave distributions in the waveguides.
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acoustic algorithm amplitude analytic solution array ARSRP attenuation Autonomous Underwater Vehicles AUVs average backscattering strength bathymetric beamforming bias bottom Chapter coefficient comparison computed Contour correlation function correlation length coupling covariance matrix depth equation equivalent surface scattering error estimated exponential far-field approximation fluctuations frequency Gaussian grazing angle hydrophone internal wave Kalman Filter levels match measurement meters mode 1 arrival mode shapes PAM1 arrival parameters peak arrival peak height pixels plotted power law distribution power spectral density predicted propagation pulse random field range region sampling scattering layer scattering strength sediment pond sequence shown in Figure shows SIA solitons signal soliton sound speed gradient sound speed variations spectrum speed and density spread standard deviation subarrivals SWARM temperature terrain terrain-relative navigation thermistor thermistor string thesis track Trackline transmission uncertainty vertical volume scattering water/sediment interface waveguide wavenumber wavenumber integration WVLA yearday