Real-Time Current and Wave Monitoring Using Acoustic and Iridium Satellite Links

The U.S. National Ocean Service (NOS) of NOAA maintains and operates a Physical Oceanography Real Time System (PORTS®) in the Nation’s major ports, harbors and bays. The traditional method of obtaining real-time data from bottom mounted instruments is via underwater cable link. However, this is vulnerable to damage and costly to install and maintain. This paper describes an approach utilizing acoustic and Iridium satellite links to report in real-time wave and current data. The system consists of an ocean bottom instrumentation platform and a U.S. Coast Guard Aid-to-Navigation buoy for data relay. The bottom platform contains a Nortek 1 MHz Acoustic Wave and Current profiler (AWAC) with an integrated Nortek Internal Processor (NIP), a LinkQuest omni-directional UWM2000H underwater acoustic transmitting modem, an ORE acoustic release-based recovery component, and a Teledyne-Benthos UAT-376/EL acoustic transponder. The surface buoy supports an omni-directional UWM2000H receiving modem, an Iridium antenna, and an electronic box containing an Iridium modem, a controller, battery packs, and temperature and voltage sensors. The AWAC measures current profiles along the vertical water column at 30-minute intervals and surface waves at hourly intervals. The NIP processes a set of user selected wave and current parameters and sends these data to the controller on the surface buoy through acoustic modems. The data are then transmitted via Iridium satellite to remote offices in real-time. Sample measurement results and reference data from a near-by Datawell’s Waverider directional wave buoy are presented. The Waverider is operated by the U.S. Army Corps of Engineers (USACE) and Scripps Institution of Oceanography (SIO). Several unique system design features and interesting wave phenomenon observed at the measurement site are discussed. The goal of this project is to demonstrate the performance of AWAC, NIP, shallow water acoustic modems, and Iridium satellite in real-time data telemetry.