Chung-Chu Teng

Wave measurements from NDBC buoys and C-MAN stations

Since the U.S. National Data Buoy Center (NDBC) deployed the first wave measuring buoy in 1973, its wave measurement network has grown very quickly. Now, all of NDBCs 71 moored buoys and 6 of its C-MAN stations measure and report ocean waves. Nineteen of the 71 buoys also measure directional waves. Over the years, NDBC has collected a huge amount of wave data. This paper briefly reviews the history of NDBC wave measurements. The basic concepts and theories of operations of NDBC wave systems are also discussed. Then, the current status and future plans for the NDBC wave measurement network are presented.

Validation of National Data Buoy Center Directional Wave Measurements Using Swell Waves from Distant Storms

Accuracy of swell wave direction measurements derived from Datawell Hippy 40-second Mark II and National Data Buoy Center angular rate sensor (ARS) are determined using two NDBC west coast stations: 46042 in Monterey Bay and 46028 near Cape San Martin. These are located in deep water 66 nautical miles apart off the central coast of California. Hippy and ARS spectral wave directions are compared to corresponding directions inferred from strong cyclonic wind fields represented by data obtained from National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/ NCAR) Reanalysis project of NOAA Earth System Research Laboratory (ESRL). Wave energy is assumed to propagate along great circle routes at its frequency-dependent group velocity. Time of wave generation is computed by the ridgeline method. Patterns found in contours of non-directional wave energy on time-frequency plots yield precise information on the time of swell generation. Frequency-dependent wave direction is determined using NDBC techniques. Swell origin position from buoy information is compared to true swell origin, determined to be where high winds exceeding 15 meters per second are found directed toward the station. We present the twelve and only cases from November 2004 to December 2005 in which peak wave period exceeded 20 seconds at NDBC station 46042. In the twelve cases, swell energy reached both stations nearly simultaneously. Storm centers were all deep extra-tropical cyclones, and these ranged across the entire Pacific Ocean. The most distant storm was 3,005 kilometers away in the southern Pacific near 60 degrees south 150 degrees west. Together, these cases show ARS-derived directions marginally exceeding NDBC error limits of 10 degrees. Accuracy of Hippy direction is estimated to be 7 plusmn 10 degrees. The viability of the validation method as a general technique for any directional wave system is discussed. The last of the twelve cases, the one with the least spectral energy density, representing a wave of period 21 seconds with an amplitude of 13 centimeters, is shown requiring further research owing to apparently weak winds around projected point of swell origin

Determination of pitch and roll angles from data buoys

Pitch and roll angles are crucial for determining directional wave information from data buoys. A gimbaled gyro sensor is typically used to provide the pitch and roll information. There are three alternatives using lighter, smaller, cheaper, and easier to handle sensors to determine this information: (1) deriving the angles by using magnetometers, (2) deriving the angles from angular rate sensors, and (3) direct pitch and roll angle outputs from a dedicated motion package. Two sets of data measured from two data buoys were used in this study. The results show the pitch and roll angles derived from angular rate sensors are better than those from the other two methods using the data from the gimbaled gyro sensor as a reference.

Concepts for an ideal ocean wave-measuring buoy

A survey of several national buoy wave data collection programs is given to establish a rough idea of the state of the art in automated wave data acquisition systems, including buoys, sensors and techniques. The largest program is that of the National Data Buoy Center, managed under the U.S. National Oceanic and Atmospheric Administration; however, the most popular commercial wave buoy is Datawell B.V.s Waverider®, followed by the OCEANOR Wavescan buoy. These two buoy types have been deployed around the world by several countries. The latest technique for wave measurement from buoys, done independently by the United States, the Netherlands, Japan and South Africa, uses displacements obtained from the Global Positioning System constellation of polar orbiting satellites. Communications systems using geosynchronous and low earth orbiting satellites and ground radio are discussed. Three concepts for improving the quality of wave data from buoys are presented.

A compact wave and ocean data buoy system

A compact wave and ocean data buoy system, called the COLOS buoy system, was recently designed and tested by the NOAAs National Data Buoy Center (NDBC) to support its expanding networks and ocean measurement capabilities. The buoy system (including buoy hull, bridle, mast, frame structure, data acquisition system, power, communications, and measurements) are described and discussed in this paper. Some results from the first field test are also presented

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 MicroStrainreg 3DM-GX1 motion sensor, located at the center of flotation, provides a stream of nine measurements subsampled at a rate of 2,048 samples in 1,200 seconds. The buoy transmits standard NDBC directional wave spectral information each hour via an iridiumreg 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. Additional, as a fifth step, a second 1.8-m buoy with a different battery pack, consisting of 700 alkaline D-cells, was evaluated and found to be adequate, yet the batteries interfered with magnetometer measurements more than the smaller, lighter cegasareg battery pack. In the sixth step, the buoy with cegasa batteries was deployed in shallow water at the U.S. Army Corps of Engineers Field Research Facility, Duck, North Carolina, from December 2006 until April 2007. This deployment provided two sources of accurate directional wave data as a basis for comparison, the FRF 8-meter array of bottom-mounted pressure sensors and a datawell waveriderreg buoy. Comparisons indicated that the 1.8-m buoy gives excellent non-directional wave spectra and accurate wave directions. A small drawback, an area of on-going research, is that the buoy gives lower than desired spreading function values. It produces characteristically lower values than does the lighter, particle-following waverider buoy. Finally, NDBC deployed an identical, second 1.8-meter buoy off Mission Bay, California, next to another datawell waverider, from February to June 2007. Directional wave accuracy, using swell waves from a distant storm as ground truth, has proven to be excellent, although, as with the first deployment at Duck, directional spreading is less than desired. We speculate this is due to size and shape of hull and limitations arising from pitch-roll signal -to-noise ratio.

Field evaluation of the value-engineered 3-meter discus buoy

In 1993, the National Data Buoy Center developed a value-engineered (VE) version of the 3-m-diameter discus buoy. The first field deployment of this design occurred in the summer of 1994 when two VE 3-m buoys were moored off the North Carolina coast. This paper presents results and evaluation of the performance of the VE 3-m design for data measurement by comparing the measured data to those measured from two standard 3-m discus buoys in a very close vicinity. In addition, a summary of future planned deployments of the buoy is also detailed.

Enhancements to NDBC's Digital Directional Wave Module

The present paper describes advancements that the National Data Buoy Center (NDBC) has achieved recently in improving its Digital Directional Wave Module (DDWM). Using the 3DM-GX1® (MicroStrain®, inc.) in the DDWM has expanded wave-measuring capability by addition of a triaxial acceleration package in place of a single, along-mast accelerometer used in the older NDBC wave system called the Angular Rate Sensor (ARS). NDBC has initiated two important changes in onboard processing. First, we transform along-mast accelerations to true vertical accelerations using measurements of pitch and roll angle. This change eliminates potential errors arising from a constant buoy heel angle. Second, NDBC has changed from a linear noise correction to an ƒ −2 inverse power function. The NDBC Engineering Laboratory has carefully tested these changes using apparatus of the Dr. Ed Michelena Sensor Test Facility, NDBCs latest mechanical wave machine, the Desktop Wave Simulator (DTWS) and a detailed electronic computational wave model, the Directional Wave Simulation Software (DWSS). The DWSS was developed to examine extreme conditions that cannot be simulated in the laboratory. It also provides a method to obtain a known input for end-to-end system testing or evaluating future on-board processing modifications. In addition, triaxial accelerations are used to determine the average pitch and roll angles of the platform without need of a separate tilt sensor. The latest version of the DDWM can be used in either directional or nondirectional modes. A compact flash memory unit is now installed as a standard feature on all DDWM units, providing high-resolution records of raw measurements.

Results of the National Data Buoy Center (NDBC) Commissioning Process on the Tropical Atmosphere Ocean (TAO) technology refreshed system

The Tropical Atmosphere Ocean/Triangle Trans-Ocean Buoy Network (TAO/TRITON) moored buoy array is a central component of the El Nino-Southern Oscillation (ENSO) Observing System to support research and forecasting of El Nino and La Nina. During the transition of the TAO array from Research to Operations, it was decided to refresh the TAO system by replacing the obsolescent components to ensure ongoing continuity of the TAO array. The major refreshed components include the data logger, subsurface conductivity/temperature (CT) sensors, and the compass for measurement of wind direction. Meanwhile, to increase the transmission frequency and transmitted data volume, NDBC determined that the Iridium communication system was ideal for the refreshed TAO system so that high temporal resolution data could be transmitted to NDBC each hour in near real-time. Accordingly, the shore-side data system for data ingest, processing, quality assurance/quality control (QA/QC), and display were modified and enhanced. To ensure the continuity and supportability of long-term ocean climate data, the TAO operations and refresh efforts follow the ten Climate Principles. NDBC designed, fabricated, integrated, and deployed several refreshed TAO buoy system to ensure sustained and smooth operations of the TAO array. To make sure that the refreshed TAO system can provide equal or better data quality from the refreshed TAO buoy system, various lab and field tests were conducted so far: (1) A lab test was conducted at NDBC by comparing the existing TAO and the refreshed TAO systems; (2) Two refreshed TAO buoys were deployed in the Gulf of Mexico for field testing; and (3) eleven refreshed TAO buoys were deployed in the Pacific Ocean next to existing TAO buoys for inter-comparison testing in the field. In addition to the Climate Principles and following all of the above parallel testing, NDBC also followed its internal process for “Commissioning New Buoys”. This paper highlights the testing that was completed in support of the Climate Principles as well as the additional support planning, support preparations, and testing required for the NDBC “Commissioning Process”. The additional Commissioning Process addresses supportability and performance aspects of the refreshed TAO system. The goal is to ensure successful and sustainable network operations.

The 2010 National Data Buoy Center (NDBC) mooring workshop

The National Data Buoy Center (NDBC) has a global operating theater that encompasses marine weather buoys, Tropical Atmosphere Ocean (TAO) buoys and Deep-Ocean Assessment and Reporting of Tsunami (DART®) buoys. NDBC operates and maintains 117 weather buoys, 55 TAO buoys and 38 DART buoys. These systems are deployed into harsh marine environments and are under constant attack from biological, environmental and human forces. NDBC realized that tackling the mooring issues associated with these deep-ocean moored buoy systems was going to be difficult and long term. In dealing with the short-term issues NDBC decided to host a two-day mooring workshop with the intention to improve the operational reliability of their moored systems. In order to better facilitate this mooring workshop, NDBC requested the NDBC Technical Services Contractor (NTSC) to bring together an internal mooring working group to address the mooring issues and problems. This paper presents the NDBC mooring configurations, the mooring working group and their finding, the actual 2010 NDBC mooring workshop and its findings and recommendations, and finally the actions and on-going efforts generated by the mooring workshop.