Towed array propagation measurements and modelling in the Philippine Sea

During the PhilSea09 experiment the US Office of Naval Research Five-Octave Research Array (FORA) was towed in various geometries making recordings of acoustic transmissions from an array of fixed sources, as well as a ship-suspended and ship-towed source. Physics issues include the structure of the convergence zone (CZ) and its dependence upon mesoscale sound speed and bathymetry, the structure of ambient noise, bottom interacting propagation and out-of-plane reverberation. In this paper, a survey of the recordings will be presented. Broadband Adaptive Beamforming techniques are applied to the array data. Direct comparison of measurements with high-fidelity broadband Parabolic Equation modelling will be presented. Much of the observed phenomenon, such as Transmission Loss (TL), Doppler spread, temporal coherence length and bottom bounce levels are well reproduced by the model. Physics issues that are not included in the modelling will be discussed – internal wave scattering, bottom roughness and out-of-p...