Deep‐water propagation measurements from a towed‐array.

Towed array measurements using the Office of Naval Research Five Octave Research Array (FORA) were made of narrowband and broadband transmissions as part of the Philippine Sea 2009 experiment (PhilSea09). Geometries between the tow‐ship and the receive ship were established to investigate the spatial and temporal structure of convergence zone (CZ) propagation, as well as short range propagation, dominated by a single bottom bounce path. Estimates of the CZ width as a function of geography and local bathymetry will be given as well as coherence scales for a constant range arc (within a CZ). For the bottom bounce path, significant bottom scattering (beam‐broadening) was observed and has been interpreted as out‐of‐plane scattering from the rough sub‐surface seafloor. Numerical modeling to begin to investigate the nature of 3‐D rough seafloor scattering work has been begun and will be presented. Implications for the detection processing for CZ and bottom‐bounce detection will be discussed.