Real-time delivery of subsurface coastal circulation measurements from distributed instruments using networked acoustic modems

Abstract

A novel system to use networked acoustic modems for real-time wireless delivery of oceanographic measurements from a distributed array of subsurface instruments in coastal waters is presented. The network consists of sensor nodes, repeater nodes, gateway nodes, and a server. Gateway nodes are buoys equipped with acoustic modems interfaced to Internet-accessible cellular modems for two-way communication between server and subsurface network. Network data flow is remotely re-configurable with multiple paths to the server from each sensor so loss or failure of an individual node can be accommodated. Oceanographic instruments are housed in bottom-mounted frames to limit biofouling and minimize fishing and shipping interference. A trawl-resistant frame enables azimuthally omnidirectional acoustic signaling as required for the network. Gateways serve multiple sensors distributed across wide areas, minimizing the number of instruments with surface exposure. A low-bandwidth data format for acoustic Doppler current profilers is devised to reduce network throughput and power consumption. Gateway equipment is engineered for a Coast Guard buoy. Tests in winter and spring indicate wind limits acoustic communications range by roughening the sea surface. A preliminary network deployment demonstrates gateway control, data delivery across multiple repeaters, and route reconfiguration.