Observations of low frequency, long range propagation in the Philippine Sea and comparisons with mode transport theory

The year-long Philippine Sea (2010–2011) experiment was an extensive deep water propagation experiment in which there were six different sources transmitting to a water column spanning vertical line array. The six sources were placed across a 250 km × 250 km area, and transmitted at frequencies in the 200–300-Hz, and 140–205-Hz bandwidth. The PhilSea frequencies are higher than previous deep water experiments in the North Pacific for which modal analyses were performed. Further, the acoustic paths sample a two-dimensional area that is rich in internal tides, waves, and eddies. The PhilSea observations are thus a new opportunity to observe acoustic modal variability at higher frequencies than before and in an oceanographically dynamic region. This talk focuses on mode observations around the mid-water depths. The mode observations are used to present narrowband statistics such as transmission loss, and broadband statistics such as peak pulse intensity, travel time wander, time spreads, and scintillation indices. The observations are then compared with a new hybrid broadband transport theory. The model-data comparisons show excellent agreement for modes 1–10, and minor deviations for the rest. The discrepancies in the comparisons are related to limitations of the hybrid model, and other oceanographic fluctuations.