Richard Bouchard

Observational changes and trends in northeast Pacific wave records

[1]xa0Routine wave observations from buoys in the northeast Pacific now extend up to 35 years. Several recent studies reported long-term trends extracted from these records. However, significant modifications of the wave measurement hardware as well as the analysis procedures since the start of the observations result in inhomogeneities of the records. We analyze significant wave heights from seven offshore wave records. Several step changes of the mean monthly significant wave height of a few decimetres are identified. These changes are induced by buoy modifications and poor data quality rather than changes in the wave climate. After adjusting the data for these step changes the wave heights show positive trends for some of the southern locations and negative trends at the northern buoys, however all trends are much smaller than reported in previous studies. Storm wave heights are extracted from the occurrence rate distributions of the adjusted significant wave heights. No statistically significant trends can be established for storm wave heights.

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.

Signal-to-noise ratio and the isolation of the 11 March 2011 Tohoku tsunami in deep-ocean tsunameter records

The United States National Oceanic and Atmospheric Administration tsunami forecasting capability under collaborative development between the National Weather Service, the Pacific Marine Environmental Laboratory, the National Geophysical Data Center, and the National Data Buoy Center depends on rapid isolation of a deep-ocean tsunami signal during tsunami propagation. Typical tsunami signal-to-noise ratios in the deep-ocean are such that de-tiding based on a combination of standard tidal harmonic predictions and carefully constructed filters are necessary to isolate the tsunami from records dominated by local tides and environmentally induced background noise. The unprecedented amplitudes measured at deep-ocean tsunameter sites offshore Japan during the propagation phase of the 11 March 2011 Tohoku tsunami provide an atypical scenario of high signal-to-noise ratios by which to evaluate the historic nature of this tsunami in terms of signal isolation for the forecasting of tsunami amplitude and inundation along Pacific Basin coastlines. Tsunami isolation for real-time forecasting during the more typical event scenarios of 27 February 2010 Chile and 29 September 2009 Samoa require specific techniques to minimize impact on the tsunami signal.

IOOS wave observations, a national perspective

The 2009 National Operational Wave Observation Plan is being updated in 2012 to reflect the present state of the wave observation network and revised to better define priority placements and upgrades, and to identify the stations with the longest data records. The revised plan, which is based on the existing 200 locations, defines a perimeter Backbone network of observing sites and proposes adding 47 new locations and upgrading the directional wave measurement of 87 stations. 10 Rover Buoys are recommended to be used with one year deployments to evaluate regional wave models so that they can be used as virtual wave gauges. The plan also identifies 60 of the existing US backbone locations with record lengths of 20 years or longer (the longest record is 38 years). These Sentinel Stations are critical to understanding climatic changes to the Nations wave conditions. In this paper, we review the status of the nations wave observation network, present a number of proposed changes and describe a process using wave models and short-term wave sensor deployments to optimize the wave observations in a particular region.

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.

U.S. deep-sea tsunameter network fully operational

In March 2008, the National Oceanic and Atmospheric Administrations (NOAA) National Data Buoy Center (NDBC) completed the deployment of the last of the 39-station network of deep-sea tsunameters. This effort was an integral part of the National Tsunami Hazard Mitigation Program. The Tsunami Program is part of a cooperative effort to save lives and protect property through hazard assessment, warning guidance, mitigation, research capabilities, and international coordination. NOAAs National Weather Service (NWS) is responsible for the overall execution of the Tsunami Program. This includes operation of the U.S. Tsunami Warning Centers (TWC) as well as leadership of the National Tsunami Hazard Mitigation Program. It also includes the acquisition, operations and maintenance of observation systems required in support of tsunami warning, such as NOAAs Deep-ocean Assessment and Reporting of Tsunamis (DARTreg), local seismic networks, coastal, and coastal flooding detectors. NWS also supports observations and data management through the National Data Buoy Center (NDBC). As part of NOAAs effort to strengthen tsunami warning capabilities, NDBC expanded the network from the original six stations to 39 stations and upgraded all stations from first-generation DARTreg I technology to second-generation DARTreg II technology. Consisting of bottom pressure recorder and a surface buoy, the tsunameters deliver sea-level data from the sea bottom to tsunami warning centers in less than three minutes. A significant capability of DART II is the two-way communications between the bottom pressure recorder and the Tsunami Warning Centers/NDBC using the Iridium Satellite LLCs commercial satellite communications system. The two-way communications allow the Tsunami Warning Centers to set stations in event mode in anticipation of possible tsunamis or retrieve the high-resolution (15-s intervals) data in one-hour blocks for detailed analysis. DART II systems transmit standard mode data, containing 24 estimated sea-level height observations at 15-minute intervals, once very six hours. The two-way communications allow for real-time troubleshooting and diagnostics of the systems. NDBC receives the data from the DART II systems, formats the data into messages and then delivers them to the National Weather Service Telecommunications Gateway (NWSTG) that then distributes the data in real-time to the Tsunami Warning Centers via NWS communications and nationally and internationally via the Global Telecommunications Systems. NDBC positioned the tsunameters between Hawaii and every seismic zone that could generate a tsunami that would impact the state and beyond, including the U.S. west coast. The effort in expanding the tsunameter network in the Pacific and to the western Atlantic, Gulf of Mexico and Caribbean required hundreds of thousands of kilometers of ship deployments. NDBC assumed operational responsibility for the tsunameter network in 2004 and the network became operational in 2005. In addition to the expansion, NDBC and its technical services contractor, SAIC, have (1) Completed the transition of the DART II technology from research to operations (2) Planned and executed 16 deployment missions needed to expand the array (3) Assisted four international partners with deployment and operation of DART II systems (4) Conducted DART II technology test procedures to facilitate and validate the commercial application of the DART II technology (5) Developed and maintain a DART observation ingest and dissemination (6) Maintained data availability in excess of the network goal of 80% (7) Introduced innovations and efficiencies in the logistics and operations that reduced the costs of maintaining the array (8) Increased the reliability of the network.