An Acoustic Telemetry System for Deep Ocean Mooring Data Acquisition and Control

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Abstract
An acoustic telemetry system is being developed which will allow two-way communication between subsurface instruments and a near-surface receiver. A high-speed link allows data to be sent from instruments to the surface in real-time, and a slower downlink is available to send commands to the remote units. The objective is to develop a cost-efficient, reliable link which will allow real-time data from anywhere in the water column to be transmitted to the surface and then forwarded via satellite link to a user anywhere on the globe. The system operates at 15-20 Khz and uses multiple frequencyshift keying (MFSK) modulation. Bit rates are adjustable, but 1200 bits per second has been selected for this application. The tones which make up the MFSK signal are decoded at the receiver with a Fourier transform implemented on a sophisticated signal processor. The processor can also be programmed to include an error-correction decoder, adaptive equalizer and data packet synchronizer. A simple, low baud rate, command link enables the use of an Automatic Repeat Request (ARQ) strategy which further increases the reliability of the up-link. A prototype system has been successfully tested at 1200 bits per second over a 3000 meter vertical path. Additional development work on the receiver, command link, and the transmitter is ongoing.

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