Instrumentation Suite for Acoustic Propagation Measurements in Complex Shallow Water Environments

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FLC Region

Security Lab

No

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Chesapeake Beach

Description

FUNCTION: Obtain at-sea measurements to test theoretical and modeling predictions of acoustic propagation in dynamic, inhomogeneous, and nonisotropic shallow water environments. The theories and models predict variations of signal amplitude, coherence, and travel time due to interaction of sound with small- to large-scale volume inhomogeneities within the water column and ocean sediment. The instrumentation suite provides calibrated measurements of these acoustic quantities in the frequency range 50 Hz to 20 kHz.

DESCRIPTION: The multiple sources and receivers in this instrumentation suite allow measurement of acoustic propagation variability as a function of both time and range over horizontal and vertical apertures. The autonomous systems can operate in severe weather conditionssince they have no sea-surface expression, while the RF telemetered receiver system can provide real-time information on acoustic propagation. The acoustic receiver systems each have an operational lifetime up to 20 days at a sampling frequency of 4 kHz. The operational lifetime for each acoustic source is ~25 days at 50% duty cycle. Clocks having rubidium-standard accuracy control all timing functions for the acoustic sources and receivers, including waveform synthesis and sampling of the received signals. This feature permits measurement of absolute travel time and its variations to better than millisecond accuracy and allows data from each of the autonomous receiver systems to be time-synced together for phase-coherent processing.

INSTRUMENTATION: The instrumentation suite consists of several acoustic sources and receiver array systems, augmented by sensors to characterize the oceanographic environment. The current equipment suite is composed of two autonomous arbitrary waveform acoustic sources, two autonomous continuous-wave acoustic sources, three autonomous 32-element acoustic vertical line array receiver systems, one autonomous 96-element acoustic horizontal line array receiver system, and one 32-element RF telemetered acoustic vertical line array receiver system.

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