Wireless Data Communication for Ocean Bottom Instrumentation

The 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 way to obtain real-time data from bottom mounted instruments is via underwater cable link. However, it is vulnerable to damages and costly to install and maintain. This paper describes a new approach utilizing wireless data telemetry. The system consists of an ocean bottom instrumentation platform and a data relay surface buoy. The bottom platform contains a RD Instruments (RDI) 1200 KHz acoustic Doppler current profiler (ADCP), a LinkQuest UWM1000 underwater acoustic transmitting modem, and acoustic recovery devices. The surface buoy supports a UWM1000 receiving modem and a Freewave 900MHz spread spectrum line-of-sight radio modem with antenna. The ADCP provides measurements of vertical current profiles at 6-minute interval and surface waves at hourly interval. The underwater acoustic modem transmits at 9.6 K baud rate the current data at the end of each 6-minute sampling, and wave data at the end of each 20-minute sampling. These data are relayed via radio at 48.5 K baud rate to a shore base station located at the University of Maryland’s Horn Point Laboratory about 16 miles away. There the data are then transferred in near-real-time via internet to NOS office in Silver Spring. Data are monitored and archived at both sites. The system was deployed off Taylors Island in the Chesapeake Bay in late July 2003 and was operated reliably through a 8-month period. It demonstrated successfully its measurement concept and capability for real-time monitoring of both currents and waves from a single ADCP instrument. This paper describes the overall system, component testings and field experiences, and presents some sample results.