Propagation of bottom interacting very low‐frequency acoustic signals off the coast near Cape Fear, NC

Abstract

The Naval Ocean Research and Development Activity (NORDA) and the United States Geological Survey (USGS) at Woods Hole, MA, conducted the Cape Fear very‐low‐frequency (VLF, 20 Hz and less) exercise off the coast near Cape Fear, NC, during June 1985. The NORDA VLF array system (16‐element vertical line array with a uniform spacing of 20 m) was deployed in 400 m of water in a bottom moored configuration. The data acquired by the array system were collected by the R/VG. W. PIERCE via a radio link with the telemetry buoy on the surface attached to the array. The USNS LYNCH towed a continuous wave (cw, 10 Hz) sound source at a depth of 91 m along tracks upslope and downslope from the array at ranges from 1–100 km. Slope angles along the tow tracks varied from 0.5°–2.0°. Signal‐to‐noise ratios of 10 dB and greater were observed on all array elements during much of the source tow. The mode structure of these signals are presented and compared with numerical predictions made by the parabolic equation and fast field program models. [Work supported by NORDA.]