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The Kauai Near-Source Test (KNST): Modeling and measurements of downslope propagation near the North Pacific Acoustics Laboratory (NPAL) Kauai source

2005; Acoustical Society of America; Volume: 117; Issue: 3 Linguagem: Inglês

10.1121/1.1854990

1520-9024

Kevin D. Heaney,

Geophysical Methods and Applications

In April 2002, a series of recordings were taken near the North Pacific Acoustic Laboratory (NPAL) Kauai source. This source transmits broadband low-frequency signals to receivers in various locations across the Pacific. Travel-time calculations based upon the nonbottom interacting PE or ray-trace modeling for the Kauai source lagged the actual first arrival by 1 second or so, a disturbing discrepancy that needed answering. The Kauai Near-Source Test (KNST) was designed to take measurements near the Kauai source to examine the effect of the local bathymetry on the signal transmitted into the ocean. Six receptions, using a 100 m VLA, at ranges from 0.2 to 52 km were taken. Parabolic Equation (PE) simulations of the channel impulse response for the measurement ranges are in good agreement with the observations. PE simulations using an exposed basalt seafloor match the data much better than those with a silty-sand cover. A primary result of this test was the indication that there may be significant energy in the first bottom bounce, comparable to the direct-path (purely refracted) ray. This implies that the seafloor near the source influences the arrival times and patterns of the field at long distances, and should be taken into account.