Development and test of a real-time wave measurement system with an Acoustic Waves and Current Profiler

The National Oceanic and Atmospheric Administration´s (NOAA) Center for Operational Oceanographic Products and Services (CO-OPS) currently maintains twenty operational Physical Oceanographic Real-Time System (PORTS^®) observatories throughout United States coastal regions. To expand its measurement capabilities, CO-OPS recently developed and tested a real-time wave measurement system featuring a Nortek 1-MHz Acoustic Waves and Current Profiler (AWAC). The test system consisted of a bottom platform assembly and a surface communications buoy. The bottom assembly contained the AWAC, a LinkQuest omnidirectional acoustic bottom modem, batteries, and a Benthos acoustic release with tethered pop-up float. The surface buoy supported a LinkQuest acoustic surface modem, an Iridium communication system, solar cells, battery, GPS receiver, and temperature and voltage sensors. A 35-day field test of this real-time wave system was conducted from June 16 through July 20, 2011, in shallow water (19 m) Atlantic Ocean region approximately 10 nautical miles off of the coast of Virginia. The site was in close proximity (approximately 190 m) to a Datawell Waverider buoy that is maintained by the Scripps Institute of Oceanography Coastal Data Information Program (CDIP). During the field test, bulk wave parameters, including significant wave height and average wave period, were transmitted real-time every 30 minutes. Raw data recorded internally on the AWAC included `burst´ samples of 2048, 2-Hz values, collected every half hour. After the AWAC was recovered at the end of the field test, raw data were downloaded and used to calculate half hourly power spectra, both non-directional and directional. The resulting field test data were used to compare measurements from the AWAC and Datawell Waverider. A description of the real-time AWAC waves system and field test performance is presented, along with a comparison of AWAC versus Datawell buoy measurements for both half hou- ly wave bulk parameters and frequency spectra.