Localizing and Beamforming Freely-Drifting VLF (Very Low Frequency) Acoustic Sensors
Abstract
Self contained, freely-drifting Swallow floats capable of recording ambient ocean noise in the 1 to 25 Hz band have been designed, built and deployed by the Marine Physical Laboratory, Scripps Institution of Oceanography, University of California, San Diego, California. The buoys are ballasted to neutral buoyancy at midwater depth where they record the components of particle velocity from which sound pressure levels may be derived. Float positions are estimated using an 8 kHz acoustic ranging system and a Kalman tracking filter. Individual float times series are then combined to obtain passive, directional acoustic measurements from 1 to 25 Hz which are not contaminated by flow noise or tether strumming. The float localization and beamforming techniques are illustrated using measurements from a September 1986 Swallow float experiments conducted approximately 50 miles west of San Diego, california. A distant target of opportunity (apparently a surface ship) provides six spectral lines between 9 and 22,5 Hz which are tracked for about 90 minutes. The complex bathymetry of the experiment site complicates signal propagation, but the signal level in the beam-former output indicates that the element time series are being properly combined.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 1988
- Accession Number
- ADA202638
Entities
People
- Richard L. Culver
Organizations
- Scripps Institution of Oceanography