Linwood L. Lee

Gas hydrate that breaches the sea floor on the continental slope of the Gulf of Mexico

We report observations that concern formation and dissociation of gas hydrate near the sea floor at depths of ∼540 m in the northern Gulf of Mexico. In August 1992, three lobes of gas hydrate were partly exposed beneath a thin layer of sediment. By May 1993, the most prominent lobe had evidently broken free and floated away, leaving a patch of disturbed sediment and exposed hydrate. The underside of the gas hydrate was about 0.2 °C warmer than ambient sea water and had trapped a large volume of oil and free gas. An in situ monitoring device, deployed on a nearby bed of mussels, recorded sustained releases of gas during a 44 day monitoring period. Gas venting coincided with a temporary rise in water temperature of 1 °C, which is consistent with thermally induced dissociation of hydrate composed mainly of methane and water. We conclude that the effects of accumulating buoyant force and fluctuating water temperature cause shallow gas hydrate alternately to check and release gas venting.

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.

TEXAS AUTOMATED BUOY SYSTEM: REAL-TIME CURRENTS FOR OIL SPILL RESPONSE

ABSTRACT If the question asked of the oil spill R&D community is, “What have you done for me lately?,” a solid answer is the Texas Automated Buoy System (TABS) and its contribution to the response effort in the 3000-barrel Buffalo Barge 292 oil spill. The TABS network consists of five automated buoys anchored off the Texas coast that report half-hourly current measurements every 6 hours under normal conditions and every 2 hours during spill events. Public access to TABS is provided via an easy-to-use Internet Web page. Because of TABS, trajectory modelers knew the offshore currents within minutes of the Buffalo Barge 292 spill and were able to continuously track the currents along the Texas coast over the next 24 days. TABS also provided the first indications of a critical current reversal during the spill that allowed planners and managers to confidently stand down response preparations (and their associated costs) in some areas while redirecting response resources to truly threatened sections of the coa...

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

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

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.

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

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.

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

The Deepwater Horizon oil spill off the coast of Louisiana in 2010 woke the country once again to the inherent risks involved in offshore drilling operations. The final overall cost of this spill will not only be measured in dollars, but also in the tragic loss of life, environmental damage to coastal wetlands and damage to the psyche of many of the local residents who once regarded the oil industry simply as a means to prosperity. Although the environment will likely eventually recover, the outrage, hardship and economic impact on local communities cannot be overlooked. Fortunately spills of this nature and magnitude are rare occurrences. Companies involved in the oil industry mitigate the chance for accidents by requiring proper personnel training, daily regular safety and toolbox meetings and regular equipment maintenance. There are standard operating procedures that must be followed for most operations on drilling platforms, tankers and fueling depots which are designed specifically to prevent the accidental discharge of oil. Still, regardless of the quality of training, equipment and procedures, some accidents will still occasionally occur. Some of these accidents will rarely, but inevitably, result in oil being discharged into the environment. Working at sea is a challenging and potentially dangerous occupation where the at sea environment can make even simple tasks difficult and hazardous. Being prepared to act on an oil spill is critical in being able to mitigate the potential impacts. Many of the people who were working on the Deepwater Horizon platform were not yet born in 1979 when the last big blowout occurred in Mexicos Bay of Campeche in the Gulf of Mexico. Some were too young to remember the Exxon Valdez disaster in 1989 and the enormity of the costs involved in cleaning it up. Events such as these led the United States government to pass the 1990 Federal Oil Pollution Act, which allowed the government and its agencies to take control of cleanup operations during an oil spill and recoup all expenses from the responsible party. This in turn led to the Texas government passing the Texas Oil Spill Prevention and Response Act in 1991. Because of the potentially large environmental and socioeconomic impact of any size spill that reaches the coast, there is a great need for timely knowledge and understanding about the environment in which the spill occurred. This is why in 1994, the Texas General Land Office (TGLO) contracted the Geochemical and Environmental Research Group (GERG) of Texas A&M University (TAMU) to develop the Texas Automated Buoy System (TABS). It is the only state funded ocean observation system in the country whose primary mandate is to provide oceanographic and meteorological data for the purpose of modeling oil spill trajectories. With nine permanent locations on the Texas shelf, the TABS system provides spill response managers in Texas with the real time data necessary to accurately predict the trajectory of an offshore oil spill so the environmental and economic impacts of the spill can be minimized. In sixteen years of operation, TABS has been used for decision making purposes in over forty events. The first few minutes after a spill has been detected are critical to determine how to treat the spill, how and where to intercept it and to determine what resources are required. The TABS system provides that vital information to allow response managers to act and mitigate the potential impact from an oil spill.

TEXAS AUTOMATED BUOY SYSTEM PROVIDES SITUATIONAL AWARENESS OF WINDS AND CURRENTS ON THE COAST OF TEXAS

Texas has established an operational system that provides observations of wind and currents to the State On-Scene Coordinator. The Texas Automated Buoy System (TABS) began in 1994 with five current...