Analysis of Internal Wave Induced Mode Coupling Effects on the 1995 SWARM Experiment Acoustic TransmissionsAs part of the Shallow Water Acoustics in a Random Medium (SWARM) experiment [1], 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 [2] 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. |
Common terms and phrases
acoustic algorithm Amplitude analysis array arrival envelope attenuation Autonomous Underwater Vehicles backscattering strength beamforming bottom Chapter coefficient comparison computed correlation function correlation length covariance covariance matrix cross-correlations depth distribution dotted Dozier and Tappert equation error estimated fluctuations frequency Gaussian grazing angle higher modes horizontal hydrophone inhomogeneities interface internal wave Kalman Filter layer levels match matrix measurement meters minutes modal mode 1 arrival Mode 1 Peak mode filters mode shapes PAM1 arrival parameters path peak arrival peak height plotted position pixels power spectral density predicted propagation pulse random field range sample SAN DIEGO sequence shown in Figure SIA solitons signal simulated backscattering sound speed gradient sound speed variations sound-speed spectrum standard deviation statistics subarrivals SWARM temperature terrain-relative navigation thermistor records thermistor string tidal Trackline transmission transponder travel-time uncertainty vertical volume scattering waveguide wavenumber WVLA yearday