NDBC wave measurement initiatives

The National Oceanic and Atmospheric Administration's (NOAA) National Data Buoy Center (NDBC) provides wave spectral and bulk, sea state parameters from its fleet of Weather observation buoys. NDBC has focused on initiatives to (1) document and improve its wave measurements and (2) make these measurements more cost-effective. This paper describes these recent initiatives, as well as plans for the future. A significant accomplishment in NDBC's efforts to document and improve its wave measurements was the post-calibration of the heading component of NDBC's operational directional wave measurement system. Prior to deployment, functional tests are performed by NDBC on sensors to confirm each measurement is within a certain tolerance. NDBC has historically documented, through field tests, an accuracy of 10 degrees for its directional wave measurements, but has not documented any post-deployment calibrations. An effort was undertaken to test five buoys after their deployment life to determine the stability of their heading accuracy. These post-deployment tests showed maximum heading errors ranging from 6 to 8 degrees, which is within NDBC's published overall accuracy of 10 degrees. NDBC also developed the capability to host two Digital Directional Wave Module (DDWM) systems on a single three-meter (3-m) buoy to evaluate improvements. This capability eliminated the cost of a second buoy and the spatial variability inherent in using two separate buoys for such evaluations. A recent modification to NDBC's DDWM is under evaluation against the present standard DDWM in the Gulf of Mexico at buoy 42003. Additionally, NDBC partnered with the Army Corps of Engineers' Coastal Hydrology Lab (CHL) on a special project comparing legacy and present-day wave systems. This comparison will help gauge potential differences in wave height observations from the newer and older systems, with the results, as anticipated by the CHL, used to improve wave models, which draw on NDBC's 30-plus years of wave height observations. Thus, a six-meter (6-m) NOMAD (Navy Oceanographic Meteorological Automatic Device) buoy, which has a boat-shaped hull, was integrated with the wave observation systems and deployed off Monterey, California near a Datawell Waverider buoy. Finally, NDBC is upgrading the DDWM, the workhorse of NDBC wave observations. This device contains a nine-axis motion sensor and processor, of which, both are commercially available, but nearing the end of their production life with newer, more power efficient and capable devices available. Thus, newer generation, motion sensors, as well as the possibility of moving the data processing to a modern, Linux-based, embedded platform, are under NDBC evaluation for their possibility of lowering both power demand and cost while maintaining compatibility with NDBC current, wave processing systems and quality standards. The Linux system will complete the processing significantly faster and likely use less power, overall. Increased computing capability will support future processing enhancements that older processing hardware cannot. Also, the new Linux system will be compatible with a desktop Linux version; thus, allowing for easier validation of any processing changes with the desktop version and previously recorded raw data. This new wave box will include NDBC Smart Module (SM) technology, for which the NDBC has a pending patent application, and allow for an upgrade to the electronics used for control and reporting, as well as maintain compatibility with the newest generation of NDBC Weather systems.