Acoustic Mode Coherence in the Arctic Ocean

The dual issues of modal decomposition for tonal sound fields and the temporal coherence of the modal amplitudes are investigated for the case of the central Arctic sound channel at very low frequencies (15-80 Hz). The performance of each of four different modal beamforming algorithms when applied t...

Full description

Bibliographic Details
Main Author: Polcari, John J.
Other Authors: MASSACHUSETTS INST OF TECH CAMBRIDGE
Format: Text
Language:English
Published: 1986
Subjects:
Acoustic Detection and Detectors
Acoustics
*ACOUSTIC ARRAYS
*BEAM FORMING
MEASUREMENT
STATISTICS
COHERENCE
SURFACE ROUGHNESS
EFFICIENCY
THESES
PROCESSING EQUIPMENT
SENSITIVITY
ICE
LIMITATIONS
LEAST SQUARES METHOD
ATTENUATION
PERTURBATIONS
ACOUSTIC SCATTERING
DRAG
AMPLITUDE
DECOMPOSITION
HYDRODYNAMICS
ACOUSTIC DATA
CHANNELS
MULTIPLE BEAMS(RADIATION)
ARCTIC REGIONS
AUDIO TONES
UNDERWATER SOUND SIGNALS
LOW FREQUENCIES
ARCTIC OCEAN
ACOUSTIC CHANNELS
ALGORITHMS
TIME INTERVALS
MODAL DECOMPOSITION
Arctic
Arctic Ocean
Arctic Sound
Online Access:http://www.dtic.mil/docs/citations/ADA216942
http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA216942
Description
Summary:The dual issues of modal decomposition for tonal sound fields and the temporal coherence of the modal amplitudes are investigated for the case of the central Arctic sound channel at very low frequencies (15-80 Hz). The performance of each of four different modal beamforming algorithms when applied to the vertical array deployed during the FRAM IV Arctic Acoustic Experiment is analyzed. A multiple beam (or decoupled beam) least squares processor produces the most acceptable results for Arctic conditions. The modal decomposition is sensitive to vertical array tilt caused by hydrodynamic drag; a technique for its estimation from the acoustic data is developed. Tonal data taken from both the horizontal and vertical arrays deployed during FRAM IV is analyzed. Horizontal array results confirm the modal amplitudes generated from vertical array data. The rough surface scattering from the ice canopy places an upper limit of 40 Hz on efficient surface duct propagation. Attenuation measurements for the first mode show excellent agreement with predictions made for ice scattering using the method of small perturbations and experimental ice statistics. The high levels of coherence observed (0.95 to 0.99) show that tonal signal propagation in the Arctic channel is essentially deterministic for time periods well in excess of one hour. Theses. Original contains color plates: All DTIC reproductions will be in black and white.

Similar Items