At-sea Observation and Theoretical Simulation on Very-low-frequency Sound Propagation in Shallow Water

摘要

A very-low-frequency (VLF) sound propagation experiment with a reflective and refractive wide-angle Ocean Bottom Seismometer (OBS) and a large volume air-gun was conducted across the northeastern continental margin of the South China Sea (SCS). With air-gun shot spacing of approximately 190 m, high-quality Scholte wave data was recorded by the horizontal and vertical geophones of OBS within 0.4-6 km offset. At least four modal phase-velocity dispersion curves of Scholte waves in the frequency band of 1.2-3 Hz were extracted from common receiver gathers (CRGs) using phase-shift method. We retrieved the first three higher modes from the horizontal component, and the fundamental and the first higher mode can be extracted from the vertical component, but no Scholte wave was found on the hydrophone. The dispersion results show that the phase velocity of the fundamental Scholte wave varies from 240 m/s to 400 m/s, and the phase velocity of the higher order of Scholte waves vary from 400 m/s to 1000 m/s.