Panama City 2003 Acoustic Coherence Experiments: Environmental Characterization

Abstract

During June 2003, the Naval Research Laboratory conducted a series of acoustic propagation experiments to measure both high (20 to 150 kHz) and low (1 to 10 kHz) frequency spatial and temporal coherence in very shallow water. Environmental data collected to support the acoustic measurements included water column current, bottom current, seasurface wave height, tide height, CTD water column profiles and mid-water time series, twodimensional micro-scale seawater temperature, and weather parameters. Wave periods varied from 3 to7 seconds and wind speeds ranged from 4 to 35 knots throughout the experiment. Temperature and salinity profiles characterized periods when the water column was isovelocity and periods when the water column was stratified with a strong depth dependence of temperature and salinity. Current magnitudes were always less than 25 cm/s. Experimental geometry and methods of environmental data collection are briefly described and environmental conditions and their impact on the propagation environment are emphasized.

Broadband Temporal Coherence Results From the June 2003 Panama City Coherence Experiments

“…During these experiments the mean of the measured broadband temporal coherence for the time scales examined was seen to be 0.47 and was relatively stationary as a function of temporal delay. This result is in agreement with [1] for the Rayleigh noise case. There was a fluctuation about the mean of approximately +/-10%.…”

“…This paper will focus primarily on mid-frequency broadband results of 20 June 2003. These results represent the effects seen during a 10-minute period on a relatively calm day with an isovelocity water column, [1]. Coherence for the entire received signal is calculated i.e.…”