NOAA???s recent field testing of current and wave measurement systems ??? part ii

The National Oceanic and Atmospheric Administration´s (NOAA) Center for Operational Oceanographic Products and Services (CO-OPS) currently maintains twenty-two operational Physical Oceanographic Real- Time System (PORTS®) observatories throughout the United States´ coastal regions. Ocean current observations are among the multiple PORTS® data products that provide critical support for safe navigation and a variety of scientific and engineering applications. To ensure that its observing network provides the most accurate and up-to-date products available, CO-OPS routinely conducts test and evaluation of newly available oceanographic sensors and measurement systems. From October 10 - December 3, 2014, CO-OPS conducted a field test in the South Chesapeake Bay which included three acoustic current profiling and wave sensors deployed in bottom mounted, upward looking configuration 1) the TRDI 500 kHz Sentinel V, 2) the Nortek 600 kHz AWAC-AST, and 3) the Nortek 500 kHz Signature 500 AD2CP; and an AXYS Technologies TriAXYS^TM Next Wave II Directional Wave Buoy with Currents provided with an integrated Nortek 600 kHz Aquadopp acoustic sensor. Also included in the deployment was a bottom mounted TRDI 600 kHz Workhorse Sentinel acoustic current profiling sensor. The test site was near the mouth of the bay where currents are predominantly tidal and the average water depth is approximately 15 meters (50 feet). During the test, currents at the site ranged in magnitude from approximately 0-0.75 m/s on a daily basis and reached as high as 1.2 m/s (2.3 knots) on one occasion. Three high-wind storm events passed through the region and significant wave heights exceeded 2 m on multiple occasions. Data results presented in this paper focus on comparison of wave measurements collected by the TriAXYSTM Next Wave II Directional Wave Buoy with Currents and the bottom-mounted TRDI 500 kHz Sentinel V. Currents measured by both devices are presented in [1]. Both - nstruments were deployed on 10 October, 2015; the Sentinel V operated until 2 November before ceasing data collection, possibly due to a faulty memory card. The TriAXYS buoy operated until recovery on 5 December 2015, transmitting wave data hourly and current data every 6 minutes via satellite in real time. Significant (Maximum) wave heights ranged from 0.15 (0.2) m to 2.5 (4.0) m and 5-7 second periods during the deployment, with the largest waves from the Northern quadrant, associated with strong northerly winds following cold front passages. In comparing bulk wave parameters, the two instruments agreed well on Maximum and Significant wave heigh and Peak period; in other measures of wave period (TMEAN and TZ), the Sentinel V showed a slight bias towards longer periods. Mean Wave Direction agreed well, to within 1 degree in the mean. Non-directional wave spectra were compared - the Sentinel V estimated these using two methods, Sea Surface Height and Velocity. The two were highly consistent and agreed well with the TriAXYS spectra, in spite of differences in methodology and frequency resolution. A notable feature of the non-directional spectra was the appearance of relative maxima of lower frequency waves (around 10 seconds) regularly appearing in the records of both instruments. Directional spectra also agreed quite well, and showed that the low frequency waves were primarily from the south, even in the presence of northerly winds, and likely from the open ocean 20 miles south at the mouth of the Chesapeake Bay. Of 12 identified QARTOD tests, 6 were applied. In general very few data points failed any of those tests; they did prove instructive on monitoring real-time data quality. The limited amount of time between instrument recovery and publication submission, combined with the significant processing required in analysis of these data sets, has resulted in limited analysis to this point. There are further data, in particular from the 5-beam Sentinel V, that need