Accession Number:

ADA073492

Title:

Some Underwater Propagation Studies in the Vicinity of the NOSC Oceanographic Tower.

Descriptive Note:

Final rept. Aug 78-Mar 79,

Corporate Author:

NAVAL OCEAN SYSTEMS CENTER SAN DIEGO CA

Personal Author(s):

Report Date:

1979-06-01

Pagination or Media Count:

42.0

Abstract:

Low-frequency 50 Hz underwater sound transmission studies were made to a range of 81 km west of the NOSC oceanographic tower off Mission Beach, San Diego, California. Both explosive and CW sources were used to ranges of 26 km, and explosive sources to longer ranges. Both hydrophones and three-component geophones were used as detectors. Results show that the propagation is better in the E-W direction, but that the noise level is higher. Thus, on the continental shelf, the N-S geophones appear to be the best detectors for sounds below 20 Hz but at longer ranges, the hydrophones have a better SN ratio. At close range 5 km propagation modes appear to be controlled by the thickness of the unconsolidated sediment. The ground arrivals indicate a semiconsolidated sedimentary layer 553 m thick with a compressional wave speed of 4770 ms. A second arrival line, having a sound speed of 3420 ms, is interpreted as a shear wave that traveled in the basement rock and was converted back to a compressional wave before reaching the surface. Overall, there was no outstanding difference between the hydrophone and geophone detectors, except the geophones do have a directionality gain of about 5 dB over omnidirectional sensors. Author ad

Subject Categories:

  • Acoustic Detection and Detectors
  • Acoustics

Distribution Statement:

APPROVED FOR PUBLIC RELEASE