Long range acoustic communications and navigation in the Arctic

A long-range acoustic navigation system with built-in acoustic communications capability has been developed for use by underwater gliders, drifters and vehicles under Arctic ice where surfacing to acquire GPS position may be risky or impossible. The system consists of multiple buoys placed on the ice with transducers suspended 100 m below, each of which is programmed to transmit in a specific time slot at regular intervals. The system operates at 900 Hz, and has programmable bandwidth, from 25 to 100 Hz. The communications data rate for the system is several bits per second, sufficient to transmit the GPS location of the buoys and several bytes of data to vehicles under the ice. The system was deployed in March of 2014 and operated through the fall of 2014, testing the performance of both the navigation and communications capabilities of the system in conjunction with Seagliders deployed by the University of Washington. Ranges of greater than 400 km were achieved with range accuracy of 40 m RMS for the case where the speed of sound is known. The long range and excellent accuracy were the result of ducted sound propagation in the Beaufort Sea.