John N. Walpert

A Comparison of Methods for Determining Significant Wave Heights—Applied to a 3-m Discus Buoy during Hurricane Katrina

Abstract In August 2005, the eye of Hurricane Katrina passed 90 km to the west of a 3-m discus buoy deployed in the Mississippi Sound and operated by the Central Gulf of Mexico Ocean Observing System (CenGOOS). The buoy motions were measured with a strapped-down, 6 degrees of freedom accelerometer, a three-axis magnetometer, and from the displacement of a GPS antenna measured by postprocessed-kinematic GPS. Recognizing that an accelerometer experiences a large offset due to gravity, the authors investigated four different means of computing wave heights. In the most widely used method for a buoy with a strapped-down, 1D accelerometer, wave heights are overestimated by 26% on average and up to 56% during the peak of the hurricane. In the second method, the component of gravity is removed from the deck relative z-axis accelerations, requiring pitch and roll information. This is most similar to the motion of the GPS antenna and reduces the overestimation to only 5% on average. In the third method, the orient...

Hurricane Katrina Winds Measured by a Buoy-Mounted Sonic Anemometer

Abstract The eye of Hurricane Katrina passed within 49 n mi of an oceanographic observing system buoy in the Mississippi Bight that is part of the Central Gulf of Mexico Ocean Observing System. Although a mechanical anemometer failed on the buoy during the hurricane, a two-axis sonic anemometer survived and provided a complete record of the hurricane’s passage. This is the first reported case of a sonic anemometer surviving a hurricane and reporting validated data, and it demonstrates that this type of anemometer is a viable alternative to the mechanical anemometers traditionally used in marine applications. The buoy pitch and roll record during the storm show the importance of compensating the anemometer records for winds oblique to the horizontal plane of the anemometers. This is made apparent in the comparison between the two wind records from the anemometers during the hurricane.

Observing and forecasting coastal currents: Texas Automated Buoy System (TABS)

The Texas Automated Buoy System operates buoys at seven sites off the Texas coast from Brownsville to Sabine in water depths ranging from ten to one hundred meters. The system is supported by the Texas General Land Office as part of its mission to mitigate the effect of catastrophic oil spills on the Texas Coast. Buoys communicate surface currents and water temperature measured at 2m depth in near real time via cell phone and commercial satellite digital data links. One buoy located at East Flower Garden Banks has a 300 kHz ADCP, a meteorology package with an ultrasonic acoustic wind velocity sensor, and a conductivity sensor. Data are posted regularly to a Web page http://www.gerg.tamu.edu/tglo and are available to the public and governments within a few hours after data collection. On the TABS Web page, a graphical map presentation of TABS current vectors has links to data tables and historical databases. Links are also provided to other data resources for oceanographic data in the Gulf of Mexico. Also on the Web page are links to an automated continental shelf forecast system that predicts currents over the Texas-Louisiana shelf on an operational basis. There are four major components in this system: (1) forecast wind field retrieving and preparation, (2) shelf circulation model module, (3) simulation plotting module and (4) Web display and file transfer module. The wind field used is a 3-hour interval ETA-22 forecast gridded wind from NOAA NCEP based on 00, 06, 12, and 18UTC model runs. The shelf circulation model is a 3-D version of Princeton Ocean Model (POM) on a domain extending from the coast to a curved line extending from 25/spl deg/N on the Mexican coast to 85/spl deg/W at the coastline of Florida. The operational POM model used at this time is a simplified barotropic version that permits us to reduce computational time to allow prediction of surface currents twenty-four hours into the future. The data vs. model comparison from April through December, 1999 of nine nearshore TABS buoys indicates modest skill of the model in predicting the wind driven circulation. A fully baroclinic version of TABS-POM model is undergoing tests and will be implemented on an operational basis when sufficient computational resources become available. We are also developing data-assimilating models of the whole Gulf of Mexico and beyond to couple to our shelf model to supply outer boundary conditions.

Evaluation of Possible Inputs of Oil From the Deepwater Horizon Spill to the Loop Current and Associated Eddies in the Gulf of Mexico

Monitoring and M A Record-Breakin Geophysical Mon Copyright 2011 b 10.1029/2011GM The results of the analyses of 282 discreet water samples collected at various depths throughout the water column in the area of the Loop Current and associated eddies in the Gulf of Mexico are reported. No subsurface colored dissolved organic matter fluorescence maximum or oxygen minimum were observed, so samples were collected at standard depths. The concentration of Deepwater Horizon (DWH) total oil equivalents (TOE) estimated from total scanning fluorescence (TSF) maximum intensities ranged from less the practical quantitation limit (PQL) of 0.70 to 5.04 μg L . The presence of petroleum could not be confirmed in two thirds of the water samples having TOE below the PQL. Forty-eight samples were analyzed by gas chromatography/mass spectrometry for polycyclic aromatic hydrocarbons (PAHs) from primarily samples with higher TOE and from a few samples at the PQ. Of these 48 samples, 35% had PAH concentrations less than or equal to the procedural blank. These concentrations are in the lower range of historical prespill reported results. The oil detected could be from the DWH oil spill as oceanographic currents could have carried the oil from the region of the spill to the sampling sites. If the DWH oil spill was the source of the hydrocarbons detected, the oil would have to have been weathered and greatly diluted by the time it reached these sampling stations. The possibility of other potential sources of oil at the sampling locations cannot be ruled out, including oil from natural seepage, small unrelated discharges, contamination from shipping activities, and atmospheric deposition. Total scanning fluorescence is shown to be a very sensitive indicator of the presence of oil and serves as a valuable screening tool.

A Look at Currents in the Gulf of Mexico in 1999 - 2000

Oceanographic conditions in the Gulf of Mexico have been extensively studied from the summer of 1999 through the fall of 2000. These studies included cradle to grave surveys of Juggernaut Eddy; surveys in the Caribbean by several consortia; oceanographic surveys in support of hurricane research in the Gulf; measurements of inflow/outflow through the Yucatan Strait; and regional nowcasts and hindcasts of circulation. Several interesting phenomena have been observed during this period, including energetic bottom currents in excess of 2 knots and bottom furrows on the continental slope; the intrusion of one of the strongest eddies in a decade into the north-central Gulf leases; and strong midwater-column currents in SE Ewing Bank (~140 cm/s). This paper describes the observational data available and summarizes ongoing efforts to understand the oceanographic conditions during this period. Eventually, it is hoped that these efforts will lead to a better estimation of offshore structure design currents; an understanding of the dynamical causes of the strong mid-water-column currents; determining whether there is a link between the strong bottom currents at the base of the Sigsbee Escarpment and the Loop Current; and assessing the skill of the regional forecast/nowcast/hindcast oceanographic models. Introduction The importance of the Gulf to offshore mineral exploration and production is well known. But what may not be as wellappreciated is the fact that, because of the wealth of observational data and observational and modeling resources that have been brought to bear on the region in recent years, a better understanding and prediction of its circulation is more feasible today than ever before. In fact, the Gulf is an ideal test bed for exploring ideas on monitoring and predicting oceanographic conditions in a coastal/marginal sea. The Gulfs circulation is dominated by the Loop Current, an energetic current of warm subtropical water that enters the Gulf through the Yucatan Strait, extends northward, then loops around to the south and ultimately exits the Gulf through the Florida Strait. The position and strength of this Loop Current (LC) exhibits considerable variability. As first suggested by Ichiye and later observed by Cochrane, the LC may extend so far north, often nearly to the Mississippi Delta, that the circulation closes off and a large warm-core (anticyclonic) eddy is shed. Like the LC, these Loop Current eddies (LCE) also have strong currents, but unlike the LC, they are not constrained to the eastern Gulf and typically drift westward at a few kilometers per day. Often, the westward drift can interfere with offshore operations. This happened in 1999 when British Borneo reported the shutdown of deepwater operations at Ewing Bank 965 due to the LC during August and September. This shutdown contributed to a

Inter-comparison and evaluation of a single-point, acoustic Doppler current sensor mounted on a TABS II spar buoy

20 million increase in development costs for the Morpeth Field. Currents in the LC and newly detached LCEs can be quite strong. Using an acoustic Doppler current profiler (ADCP), Cooper et al surveyed two LCEs in 1983 and recorded 223 cm/s (4.3 knot) surface currents. Measured currents during Fast Eddy were slightly lower reaching 180 cm/s (Forristall et al) After separation from the LC, the eddies decay and speeds slowly decrease. In the case of Fast Eddy, this slow evolution is described by Lewis et al. On a smaller scale, shingles, filaments and small eddies may be formed by instabilities associated with the LC and LCE fronts. Vukovich et al found that some of these smallscale features were noticeable to 700 m depth and propagated along the Loop Current boundary at 28 km/day. In the fall of 1999, the LC shed Juggernaut Eddy which traversed active lease sites in the northern Gulf before moving off to the southwest. A similar event occurred in 1989 when the LC moved into southeast Ewing Bank before shedding Nelson Eddy. As part of a long-term effort to better understand the Loop Current system and its variability and to develop the tools needed to accurately nowcast/forecast these OTC 12996 A Look at Currents in the Gulf of Mexico in 1999 2000 K.J. Schaudt Marathon Oil Co., G.Z. Forristall Shell Global Solutions U.S., L.H. Kantha, R. Leben, J.K. Choi Univ. of Colorado, P. Black, E. Uhlhorn NOAA, N.L. Guinasso, Jr. and J.N. Walpert TAMU GERG, F.J. Kelly TAMUCC, S.F. DiMarco and O. Wang TAMU OCN, S. Anderson, P. Coholan Horizon Marine 2 SCHAUDT ET AL OTC 12996 features, this eddy was extensively monitored and studied during its formation and transit. Observations and Numerical Models Due to a fortunate confluence of efforts by industry, government and university researchers, the Gulf was very well described in 1999 and 2000. Here we describe the comprehensive observations collected during this event and report on the current state of numerical circulation nowcast/forecast models for the Gulf. NOPP Airborne Surveys. As part of the National Ocean Partnership Program (NOPP) Gulf of Mexico Ocean Monitoring System (GOMOMS) program, Naval Oceanographic Office (NAVOCEANO) undertook airborne expendable bathythermograph (XBT) surveys in the Gulf. Fig. 1 shows the survey tracks in 1998 and 2000. NOPP Vessel Surveys. Two efforts are of interest here. As part of the NOPP GOMOMS program, Juggernaut Eddy was surveyed in late October 1999 as it separated from the Loop Current (Fig. 2). Oceanographic measurements were also collected across the Yucatan Strait in October 1999 to better understand the inflow conditions. Fig. 3 shows near-surface currents measured along the Yucatan Strait. Near surface flow was generally northward with speeds exceeding 100 cm/s over much of the section. There was also a significant backflow from the Gulf into the Caribbean on the Cuban side. Hurricane Research Division. During the course of hurricane research, NOAAs Atlantic Oceanographic Marine Laboratory conducted expendable bathythermograph (XBT) surveys of the Gulf of Mexico before, during and after the passage of hurricanes through the Gulf of Mexico in 1999 and 2000. The survey tracks in early October 1999 are typical of the coverage (Fig. 4). Inflow/outflow surveys. In order to improve the skill of numerical nowcast/forecast modeling, the inflow region in the Yucatan Channel and the Caribbean was extensively studied by a coordinated effort between NOPP, Conocos Eddy Joint Industry Program (EJIP) and Texacos Deepstar project. Current meter moorings were deployed in the Yucatan Strait. The array spanned both the Mexican and Cuban sides of the Strait and the moorings had several current meters to sample the vertical structure of the inflow. ADCPs were also deployed on all of these moorings. ADCP and Conductivity/ Temperature/Depth (CTD) surveys were made across the Strait during deployment and retrieval of the current meters. Also, airborne XBT (AXBT), airborne expendable CTD (AXCTD) and airborne expendable current profiler (AXCP) surveys were made in July 1999, March 2000 and July 2000. The surveys were conducted along the ground tracks of the TOPEX altimeter to enable using altimetry to provide conditions along the open southern boundary of numerical nowcast/forecast models of the Caribbean and the Gulf. EJIP Surveys. Starting in October 1999, EJIP conducted a series of current and temperature surveys of Juggernaut Eddy from its formation in the central Gulf to its decay in Mexican waters. Moorings and Rig Observations. Currents were measured at numerous locations in the Gulf, both from moorings and from fixed and mobile platforms. Many of the historical datasets and the numerical hindcast modeling are described in greater detail by Texas A&Ms work in the Deepwater Physical Oceanography Reanalysis and Synthesis of Historical Data (TAMU) project. This effort, funded by the MMS, is pooling and analyzing industry and public current data. One of the most significant recent efforts is the three moorings deployed for the MMS at approximately the 2000 m isobath in the central Gulf in Atwater Valley 663, Green Canyon 744 and Atwater Valley 838 from August 1999 through August 2000 (TAMU). The MMS moorings and the location of representative industry moored, platform or drilling rig-based current measurements are shown in Fig. 5. Most of the industry sites used ADCPs deployed from drilling rigs for roughly 90-day periods. In order to better understand the Topographic Rossby Waves, which are hypothesized to cause strong deepwater currents, Fugro GEOSs Gulf Lower Layer (GULL) Current Measurement Project recently deployed 19 current meter moorings in water depths from 5,000 to 11,000 feet (Fig. 6). CODAR Observations. Increasingly, CODARS (H/F RADAR systems for mapping currents) are being used to monitor and study near-coastal surface currents in the Gulf. Surface currents at the Morpeth platform (Fig. 5) were measured using a CODAR Seasonde. Testing of two longrange CODARS with the ability to map currents within a 300 to 400 km radius began in 2000. Assuming successful test results, long-range CODARS will be deployed to operationally map the currents in the Exclusive Economic Zone (EEZ) offshore Louisiana. Fig. 7 shows the overlapping region where hourly current vectors would be mapped at approximately a 6 km resolution and the large region with radial coverage. Altimetry. Ready availability of real-time data streams from NASA/CNES TOPEX/Poseidon altimetric mission and the ESA ERS-2 has enabled continuous monitoring of the Gulf as well as provided input into nowcast/forecast models of the Gulf (see for example, http://www-ccar.colorado.edu/~leben/ research.html). An example was shown in Fig. 2. Excellent altimetric coverage has existed since 1993 and is expected to continue well into this decade with the JASON-1, the successor to the TOPEX altimetric mission. Drifters. Lagrangian drifters have enabled the circulation in the Gulf to be monitored since the eighties. Horizon Marine deploys drifters drogued at 50 m depth, as part of their Eddy Wa

Interdisciplinary Ocean Observing on the Texas Coast

The Geochemical and Environmental Research Group of Texas A&M University conducted a thirty-day field experiment to compare and evaluate a single-point, Doppler current sensor for use on the Texas Automated Buoy System (TABS) spar buoys. Two spar buoys were deployed within 200 m of each other approximately 22 nmi. southwest of Galveston, Texas, in the Gulf of Mexico. One buoy was equipped with a Marsh-McBirney model 585 electromagnetic sensor and the other with an Aanderaa model DCS3500R single-point acoustic Doppler sensor. The sensors were located 2.5 m below the surface. A 300 kHz RD Instruments Workhorse Sentinel was moored in an upward-looking mode between the two buoys. Statistical comparison of the data from the three sensors shows that they performed well and measured vector components of similar magnitudes. Data from the Aanderaa DCS3500R tracked the bottom-mounted ADCP more closely than did the MMI585. The experiment indicates that both the MMI585 and the Aanderaa DCS3500R are suitable sensors for spar buoy deployment in a near surface dynamic environment. Of the three sensors, the MMI585 was most sensitive to fouling.

The effects of marine fouling on the performance of a single-point acoustic Doppler current sensor mounted on a TABS-II spar buoy

This article describes Texas A&M Universitys existing interdisciplinary operating Ocean Observing System (OOS) and supplemental instrumentation added to address spatial and temporal scales of northern Gulf of Mexico coastal hazards. Details are also included in Texas A&M Universitys future directions as an OOS leader on the Texas shelf and in how OOSs plays a vital role in community education and awareness of the coastal oceans.

High speed two way data communications used in the Texas Automated Buoy System (TABS)

Following the successful results of an experiment conducted during June and July, 2000 to determine how a single-point, acoustic Doppler current sensor would perform on a TABS-II spar buoy, a second experiment was conducted to determine the effects of marine fouling on the sensor. The TABS-II spar buoy is one of two types of spar buoys used by the Geochemical and Environmental Research Group (GERG) to monitor and report near real-time surface currents, in support of oil spill response and trajectory modeling for the Texas General Land Office in Austin, Texas. An Aanderaa DCS3500R Doppler current sensor was mounted on a TABS-II spar buoy and moored at a location approximately 22 nmi southwest of Galveston, Texas in 19 in of water. The mooring remained in place from June 1 to December 15, 2000 during which time it reported hourly near-surface current components and temperature via satellite telephone to GERGs office in College Station. On November 15, 2000 a second TABS-II spar buoy, equipped with a clean, calibrated, Marsh-McBirney, Inc., (MMI) Model 585 electromagnetic sensor, was deployed 200 in downcoast of the DCS3500R-equipped buoy. A 600-kHz RD Instruments directional-wave ADCP was mounted on the bottom between them in an upward-looking configuration. On November 15, 2000, prior to deployment of the MMI-equipped buoy and the ADCP wave meter, the DCS3500R-equipped buoy was recovered to remove marine growth from the hull and mooring. Barnacle growth on the DCS3500R was extensive, covering the entire sensor and cable.

Texas Automated Buoy System - sustainable ocean observations to help protect the environment

The goal of obtaining cost effective, reliable, two-way data communications with remote instrumentation has always been a major technical challenge in the successful operation of a remote ocean observing system. Typical low-cost telemetry methods such as line-of-sight radio and cellular telephones are limited in their coverage and are not suitable for remote locations, such as offshore moored buoy platforms. Power limitations, space availability and high volumes of data, have made this goal even more difficult to achieve. Satellites have typically provided low data rates at relatively high costs compared to other telemetry methods available to near shore deployment applications. Most satellite telephone systems were designed around the needs of the trucking or rail industry, and have typically relied on either mechanically steered or large tunable mast antennas as well as high current electronics to achieve two-way data communications through geo-synchronous satellites. In 1991 a consortium comprised of twelve aerospace and telecommunication companies was formed to provide worldwide satellite telecommunications service to business, government and the public. Their purpose was to provide cost effective satellite voice and data communications to areas, which were under-serviced. They named the consortium Globalstar/spl trade/ and over the next 10 years put into orbit, 48 LEO (Low-Earth-Orbit) satellites. Although primarily developed for voice communications in remote areas, Globalstar/spl trade/ Satellite Communications System offers full duplex, two way, data communication through the Qualcomm GSP-1620 Packet Data Modem, at uplink and downlink speeds of 9600 bps. In January 2002, the Geochemical and Environmental Research Group (GERG) of Texas A&M University (TAMU), deployed a TABS II buoy in the Gulf of Mexico, at the Flower Garden Bank Marine Sanctuary equipped with the new modem. The small, robust antenna, low power requirements and high speed data telemetry have so far proven to be reliable and a cost effective means to achieve two way data transmission of moderate to large data volumes.