National Data Buoy Center 1.8-meter Discus Buoy, Directional Wave System

Since year 2005, the National Data Buoy Center (NDBC) has been developing, testing, evaluating and refining a pitch-roll-heave directional wave measuring system. It consists of a 1.8-meter-diameter isomer foam flotation ring in the center of which is placed a cylindrical battery and instrument compartment. A MicroStrain 3DM-GX1 motion sensor, located at the center of flotation, provides a stream of nine measurements sub-sampled at a rate of 2,048 samples in 1,200 seconds. The buoy transmits standard NDBC directional wave spectral information each hour via an Iridium (R) satellite modem after computing directional wave spectra from triaxial components of earth magnetic flux density and angular rate, and along-mast acceleration. Additionally, high-resolution data are stored onboard the station for post-deployment analysis. Testing has been done in seven steps. First, static testing of the 3DM-GX1 revealed that the measurement mode of the sensor yields varying amounts of electronic and processor noise. The best mode and time constants for the sensor were determined in the second step of development, using a desktop wave simulator designed exclusively for that purpose. It provided precisely known simulated directional wave information. In the third step, the complete buoy payload, including an air-depolarized, alkaline battery pack manufactured by Cegasa International was placed on the one-meter radius NDBC directional wave simulator, with which a full end-to-end test was conducted. Fourth, after sufficient laboratory testing, the complete system was deployed near NDBC station 42007 in the northern Gulf of Mexico for several days, and there was found close agreement between measurements from the two platforms.
See also ADM002047. Presented at the MTS/IEEE Oceans 2007 Conference held in Vancouver, Canada on 29 September-4 October 2007. Published in the Proceedings of the MTS/IEEE Oceans 2007 Conference, 2007. The original document contains color images.