A New Buoy for Oceanographic and Spill Response Applications

Transcription

1 A New Buoy for Oceanographic and Spill Response Applications John N. Walpert, Norman L. Guinasso Jr., Leslie C. Bender Geochemical and Environmental Research Group Texas A&M University Abstract In 1995 the government of the state of Texas through the Texas General Lands Office (TGLO), began a proactive program of current monitoring in the Gulf of Mexico to support its oil spill trajectory modeling efforts. Texas A&M University s Geochemical and Environmental Research Group (GERG) was contracted to develop and operate a near real time observing system to provide this valuable data. The use of historical currents in spill response models had been shown over the years to be unreliable and unable to account for shifts in local environmental forces. After fourteen years of operation, the Texas Automated Buoy System (TABS) is still providing data to support TGLO s mandate of oil spill trajectory modeling and response at up to 8 TGLO sponsored locations and 2 industry sponsored locations off the coast of Texas. The TABS system has been used for decision making purposes in over 30 spill events since Since the inception of TABS a diverse fleet of buoys have been developed with the capability to provide high quality oceanographic data that supports not only the TGLO mandate of near surface currents, but can also provide meteorological, biological, chemical and directional wave data for research, education, search and rescue (SAR), fisheries etc.. In recent years, the increasing high cost of oil has prompted the oil industry to transport heavier grades (specific gravity > 1.024) of oil which when spilled leave little or no surface expression. In 2005, the DBL-152 spill discharged 70,000 barrels of heavy fuel oil into the shallow waters of the Gulf of Mexico. With no surface expression to guide them, and only near surface current information available, trajectory modeling and cleanup of the spill was difficult, time consuming and very expensive. A TABS II buoy equipped with a Doppler profiler and meteorological sensors was later deployed at the spill site to provide local real time data. A deployment ship equipped with crane, winch and open deck space was required along with trained technicians to deploy, test and configure the buoy for operation. It was determined then that a small, lightweight, preconfigured buoy which could be deployed by any ship of opportunity at the spill location would be extremely useful and cost effective. In September 2008, GERG was funded to design a small lightweight buoy to provide real time current profiles or near surface currents, meteorological, and directional wave data. TABS an integral component of the oil spill trajectory modeling efforts that were being used to help mitigate the effects of oil spills along the Texas Gulf coast [1]. The Geochemical and Environmental Research Group (GERG) of Texas A&M University was chosen to develop a cost effective system that would satisfy this mandate. Working in conjunction with the Woods Hole Group Ltd., out of N. Falmouth, MA. to design the buoy and electronics, GERG deployed the first system in April, Seven locations along the Texas coast were chosen based on their proximity to coastal populations, ports of entry for oil tankers, lightering locations and industry activity. These locations (Fig. 1) are spread along the coast from Port Isabel near the border with Mexico to Sabine Pass near the Texas Louisiana border. In 2002, two additional sites at the east and west Flower Garden Banks were added. These two sites are funded through a consortium of oil companies which support the Flower Garden Banks Joint Industry Project (FGJIP). A tenth location was added in 2005 in support of a NOAA sponsored project directed by Dr. Lisa Campbell at Texas A&M University. The study made use of a new flow cytometer called FlowCam for detecting a particular type of diatom called karenia brevis which causes harmful algal blooms. The TGLO sponsored a 3m discus buoy in support of this project which also served as a working TABS buoy and a TABS development site for new sensors. Along with the FlowCam (flow cytometer) development this buoy also was used for testing new meteorological sensors, nutrient analyzers and flourometers, some of which have now been deployed at more traditional TABS locations. I. INTRODUCTION October 2009, will mark the 15 th anniversary of the beginning of TABS (Texas Automated Buoy System). TABS came about by a request from the Texas General Lands Office (TGLO) for the development of a real time near surface current measuring and reporting system along the coast of Texas in the Gulf of Mexico. The design concept would make Figure 1: Distribution of TABS buoys in the Gulf of Mexico

2 II. SYSTEM DEVELOPMENT The first TABS buoy (Fig. 2) was a spar design and consisted of a Woods Hole Group SeaPac current meter coupled to a cell phone modem and solar cells for power. The spar design was specifically chosen for the hull because of GERG s mandate to provide high quality near surface current measurements. The spar design is not a wave follower and high frequency waves tend to roll through the buoy while lower frequency waves tend to make the buoy move vertically through the orbital motion rather than follow the slope of the waves. Called a TABS I buoy, the first system provided half hourly near surface currents and water temperature measurements every 3 hours via cell phone modem. Although there were many issues with the first buoys, the concept was solid and was used as a foundation in improving the system and later developing more advanced electronics and sensor combinations. The buoy could be deployed in waters up to 40m in depth using a traditional chain or chain and wire catenary mooring design [2]. Working with the Woods Hole Group, GERG introduced the TABS II buoy in The TABS II had the expanded capability of collecting meteorological data, as well as full water column ADCP data and near surface current information. It also had additional ports for sensor expansion. The buoy was approximately twice the size of a TABS I buoy, and was capable of being deployed in deeper water. Initial attempts at meteorological data collection failed due to poor design and the robustness of sensors small enough to fit on the top of a small spar buoy. The introduction of ultrasonic and sonic anemometers solved this problem and development of a dry plumbing system also enabled collection of Figure 2: First TABS I buoy being deployed in April 1995 Figure 3: Early version of a TABS II with Westinghouse satellite antenna. barometric pressure data. The unique design of the TABS I and TABS II buoys also introduced deployment and recovery issues. Stainless steel handles mounted at the waterline which were used for deployment on the early TABS II buoys had to be removed because boats would use them as tie off points. The larger commercial boats would end up breaking sensors and antennas and dragging the buoys off of location. This caused a lot of extra service trips to the buoys at a cost of tens of thousands of dollars per occurrence. GERG was left with no alternative but to remove the handles. This had implications on how the buoys would be deployed and recovered. The removal of the handles left no easy way to lift the buoy and put it in the water or take it out without submerging the top of the buoy and the entire meteorological sensor system. The resulting deployment method required that the TABS II buoy be placed on rollers on the stern of the ship so it could be simply pushed off the open back deck. Recovery involved dropping a wire rope lasso over the top of the buoy and allowing it to sink beneath the buoy onto the mooring chain. Then when the lasso was winched in it would pick up the mooring allowing the buoy to fall over and be dragged up on deck. This method has worked very well over the years but it requires a ship with an open stern and significant back deck space, which limits the number of vessels suitable for deployment or recovery. In the end the removal of the handles reduced the number of tie offs and damage to the buoys. Because the TABS II buoys could be set in deeper waters, most of the deployment areas were outside of traditional cell phone coverage areas. Satellite transceivers, made by Westinghouse, and using the AMSC

3 and MSAT geostationary satellites, were used as a replacement for the cell phones. These transceiver systems were large, consumed a lot of power and were expensive to operate. The antennas were 48 whip antennas which had to be tuned to their geographic location and were fragile at sea. Although the system worked, the fragile nature of the antennas was a serious problem. The Westinghouse system was soon replaced by Globalstar in 2001 as soon as Qualcomm came out with the GSP-1620 satellite data modem. This change resulted in a major improvement in power consumption, data throughput, system reliability, robustness, and a reduction in service cruises by approximately 40%. Besides reducing service cruises, the cost of data dropped by 50% [5]. Data throughput went from approximately 75% to 98-99% after quality control. The next few years saw a change in the electronics design of the TABS II buoy from the Woods Hole Group Remote System Manager as a controller to a new ultra low power PC-104 based controller. This change gave the buoys much more computing capability, sensor options, and reduced service time and trouble shooting requirements. The new processor has a Linux based OS and modular programs that are written in Perl and in C [6]. 900 cover impregnated with Samthane coating, and a rectangular instrument well. The new buoy provides over 4000 lbs reserve buoyancy and because it is a discus hull and a wave following design, it can measure directional waves along with the traditional near surface and profiled currents, redundant winds, barometric pressure, air temperature and humidity, salinity and water temperature. There is the capability for adding additional sensors such as flourometers, transmissometers, nutrient sensors, par sensors etc. There are currently three of these buoys deployed in the Gulf of Mexico as part of TABS and the Flower Gardens Joint Industry Project (FGJIP) and one which has been fabricated for the University of Southern Mississippi. The greatest weakness of the TABS II buoy over the years has proven to be its reserve buoyancy. In order for the buoy to behave as a spar buoy, its motion has to be heavily damped. It is moored using a semi-taught catenary chain and wire rope mooring which results in a reserve buoyancy of approximately 800 lbs. During a major hurricane, there is not sufficient reserve buoyancy to keep the buoy on the surface even when there is a large mooring scope of 1.7:1. After losses during hurricanes Claudette, Ike and Dolly, it was determined that a larger buoy would be more useful in deeper water. Figure 5: TABS 2.25m buoy at Flower Garden Banks site N III. MODELING EFFORT Figure 4: Latest version of TABS II with MET station and Globalstar system In 2007, work commenced on a new 2.25m discus design (Fig. 5) that made use of the existing PC-104 controller but with additional capabilities such as wireless control, wave data, a hull made from closed cell foam with a woven Spectra All data collected by TABS buoys are used by the TGLO and NOAA HAZMAT personnel in support of spill trajectory modeling during cleanup operations following an oil spill. Data collected at GERG are distributed to clients and the general public via FTP server and via the World Wide Web at Also available on this website are a detailed real time analysis of the oceanographic and meteorological data. The goal of the TGLO and NOAA HAZMAT modeling effort is to locate and cleanup the spill before it has an impact on the coastal environments such as beaches, shell reefs, nursing grounds, and the economic well coastal Texas. Data show [4] that the coastal currents off of Texas are generally topographically driven and are affected by local weather fronts and local bottom features. The Princeton and Regional Ocean Models (POMS and ROMS) run daily by the Department of Oceanography at Texas A&M use TABS buoy inputs along with data from NCEP (National Center for Environmental Prediction) to model currents on and off the Texas shelf. The models cannot take into account small scale

4 local weather and effects of local bottom topographies at spill sites because the data inputs are not available. This becomes especially important when there is a spill consisting of oils with specific gravities greater than about 1. These oils sink into the water column or to the seafloor leaving little or no surface expression making them very difficult to track. This is less of a problem in deep water than it is in shallow waters of about 40 meters or less. In this zone wave and wind energies can re-suspend oils on the seafloor driving them back up into the water column and current then potentially, eventually onto land where they coat beaches and end up as sticky tar balls. TABS buoys are spaced far apart along the coast requiring currents at the actual spill site to be modeled by using surface currents and winds from TABS locations and extrapolating results at the spill site. When there is a spill of heavy oils, this method may not provide the necessary information to optimize the trajectory model outputs. During spill events offshore of states where there are no existing buoys in place to measure real time currents, modelers must rely on historical current data for their trajectory models. More up to date local current information, whether it is near surface or near bottom, is required to help fill in the gaps. Although traditional TABS buoys can and have been deployed on site at oil spills, large buoys which can provide all the data necessary for the models require a considerable amount of time to configure for the actual site depth and data requirements. Traditional TABS buoys require trained technicians for setup, deployment and recovery as well as a suitable ship with proper lifting gear and open deck space. IV. ON SITE DATA In November 2005, the DBL-152 spill occurred near Port Arthur, Texas when an oil barge struck a piece of submerged wreckage left over after Hurricane Rita. The hurricane debris ripped a 30 foot long gash in the hull of the barge which resulted in 70,000 barrels of heavy fuel oil being spilled into the Gulf of Mexico (Fig. 5). At the request of the NOAA HAZMAT people and the TGLO, GERG deployed a TABS II buoy equipped with both a near surface current sensor, and an ADCP. The buoy was on location for approximately 3 months as crews tracked and recovered the submerged heavy fuel oil. In order to deploy the buoy, two GERG technicians spent 3 days getting a buoy ready to go then accompanied the buoy to a chartered vessel for deployment. It was felt that a small preconfigured lightweight buoy which could be handled by two inexperienced deck hands would be very cost effective in these situations. In September 2008, GERG was awarded funding by the Texas General Lands Office to produce two prototypes of a fast responder buoy. Both prototypes would initially use Globalstar for telemetry and transmit data to the TABS operations center at GERG where the data would be distributed via FTP server and Internet. One buoy would measure near surface current while the other would measure current profiles using an ADCP. The buoys were dubbed Figure 5: TABS II deployed on site at the DBL-152 oil spill in The buoy measured near surface currents and current profiles along with winds to aid the spill cleanup. (Photo courtesy of NOAA) Responder buoys because the design requirement was fast response, easy assembly and easy deployment. Sensor requirements for the new TABS Responder were determined to be full water column currents using an ADCP for heavy oil spills, or near surface currents using a single point Doppler current sensor for lighter oil spills, water temperature, wind speed and direction, barometric pressure, directional wave information and GPS position. The buoy had to be small enough to be easily handled on deck by two people without the aid of special equipment for deployment purposes and it had to be pre programmed so inexperienced deck hands could easily deploy the buoy without having to program or open the buoy at all. The average time a vessel is on site for an oil spill clean up will vary according to oil type, weather conditions and location. The amount of time a cleanup vessel spends at any one spill site, defines the necessary deployment duration of a fast response buoy. For the purposes of designing a fast response buoy, a period of 3 to 4 weeks was used. A buoy satisfying these requirements would supplement TABS during oils spills in the Gulf of Mexico, but could also be easily shipped on short notice anywhere in the country where there was an oil spill. Sensors were chosen based on power requirements, size, weight and ease of integration. An ultra low power, stripped down, PC-104 format computer running at 100 MHz was chosen as a controller (Fig 6). The processor was selected because it was very low power, it was sufficient to handle the computations required for the directional waves, it would run

5 Linux and use existing GERG buoy software for file management, telemetry, scheduling etc. Some of the programs and operations still had to be re written because of the type of processor in the new computer. This turned into more of a challenge than expected, but was eventually accomplished within the budgeted time frame of the project. New sensor software was written in C while the major operations such as scheduling, file management, telemetry were written in Perl. The overall power requirement for the buoy was determined to be approximately 45 watt-hrs/day based on hourly satellite transmissions, hourly wave measurements and measurement of other parameters at half hour intervals. Several power options were examined based on power density, cyclical memory, space requirements and discharge characteristics. In the end, lithium ion batteries were chosen to power the system. The power pack was designed into a frame which fits inside 6 by 17.5 long aluminum cylinder and included the charge controllers, charge monitoring electronics and power distribution board. The power supply provides 950 watt hrs at 15V dc with a very flat discharge curve. This is sufficient to allow 21 days of operation in the default setup. In order to keep costs down and conserve size and weight, it was decided not to use solar panels to keep the batteries charging while deployed. At the end of the deployment duration, the buoy is recovered and charged on the deck of the ship by plugging in to a bulkhead connector on the top plate of the buoy. There are two sealed housings which make up the watertight structure. Both housings are hard anodized and make use of double O-ring seals. The battery housing bolts to a bottom plate on the underside of the buoy. The current sensor is mounted to the bottom of the battery housing (Fig. 7). The controller electronics were designed into a separate 6 inch diameter cylinder which mounts to the top of the bottom plate. This housing contains the buoy controller, serial interface and power distribution board and voltage regulator, accelerometers, computer power supply, and sensor boards. The housing passes through the center of a foam hull where it is held in place by a top plate which sandwiches the foam hull. With the exception of the Aquadopp profiler, each sensor contains its own compass. The framework holding the electronics was designed to allow easy assembly while automatically aligning the current sensor with the compass. The battery housing and the electronics housings each bolt to small plates which sandwich the foam hull and form the bulk of the buoy (Fig. 8). Hull shape was determined based on the need to measure directional wave information in a short period coastal environment. The basic discus hull was chosen with a single chine at a 33 degree rise from the base of the hull to the waterline (Fig. 7). The 6.3 cu. ft. hull has an outside diameter of 36 inches which provides sufficient buoyancy to withstand strong currents and high winds in 40 meters of water using a light mooring with a 1.3:1 scope. The net buoyancy including payload was determined to be approximately 280 lbs. Specifications for the buoy are given in Table 1. Figure 6: Electronics and controller assembly for the Aquadopp equipped Responder Buoy Fig. 7 Battery Housing with Aquadopp current sensor installed A mast measuring 1.5m from the water line to the sensors supports a Qualcomm GSP-1620 satellite modem, night flashing amber light, tri-lens radar reflector and an Airmar meteorological sensor which provides compass corrected wind speed and direction, barometric pressure and GPS location. The mast is the most vulnerable component of the buoy in terms of potential for being damaged. With the sensors mounted only 1.5m above the sea surface, there is always the potential for wave or ship damage. All cables which enter the electronics housing do so through proper bulkhead connectors (as opposed to glands) so even if the mast were to be sheared off, the integrity of the electronics housing and battery compartment would remain intact. The bulkhead connectors are mounted under the mast on the electronics housing top plate and are protected by the buoy s top plate (Fig. 9).

6 the batteries, monitoring the charge status and turning the buoy on and off. All of the components mounted on the mast are designed to be easily replaced if they are damaged in any way. The TABS Responder was designed to enable non technical or inexperienced personnel to easily turn on or charge the buoy without having to open it up and expose the electronics. The buoys are pre-configured before they leave GERG based on water depth and current sensor (Table II). When personnel on the boat uncrates the buoy all they have to do is plug in the mast electronics, turn the buoy on and deploy the buoy. This can be done from any vessel regardless of whether or not it has lifting equipment. Figure 8: Hull shape and light mooring were designed to allow the buoy to respond to high frequency waves In its default setup, the buoy will transmit data every 60 minutes via Globalstar using Qualcomm s GSP-1620 packet data modem. Although data are compressed for transmission, because the buoy measures directional waves and profiled currents, short burst, simplex data is not an option. Initially, satellite data will be quality controlled at GERG and posted to the web for access by modelers and possibly the cleanup fleet. Future versions of the buoy may transmit data directly to the client if that is a preference. Future buoys will also have the capability to use free wave radio or cellular telephone to transmit data directly to the cleanup fleet or a shore station. Figure 9: The buoy is shipped completely assembled with the exception of the weather mast which just plugs in and bolts in place. TABLE I TABS Responder Specifications Hull Material/Type Softlite Foam/ Discus Subsurface Metals 5086 Aluminum/316-L SS Above surface Metals 6061 Aluminum/316-L SS Assembled Diameter 0.9 m Air Weight (fully assembled) 68 kg (150 lbs) Reserve Buoyancy 127 kg (280 lbs) Max. Site Depth (for ADCP) 40m (130 feet) Deployment Duration (est.) 21 days from full charge Time to Full Charge 9 hrs from flat batteries Current Sensor Depth 0.75 m MET Sensor Altitude 1.5 m One of the bulkhead connectors is reserved for monitoring buoy operation, uploading software or downloading recorded data, a second connector passes signals and power for the mast mounted sensors and telemetry, and the third is for charging Figure 10. TABS Responder during a test deployment in the Gulf of Mexico

7 TABLE II TABS Responder Default Settings Wind Speed and Direction 10 min. average every 30 min. Barometric Pressure 30 min GPS Position/Time 30 min DCS Frequency 2 MHz # Pings/average/Cycle 300 pings/5 min/30 min. Aquadopp Frequency 600 khz Bin Length 1m # Bins 42 or 22 depending on depth Average Length 5 min # Pings/average 300 IMU Sample Rate 100 Hz IMU Sample duration/cycle 15 min/hr Recorder Size 8 Gbyte [4] Walpert, J.N., N.L. Guinasso, Jr., L.L. Lee III, F.J. Kelly, 2000: Inter-comparison and Evaluation of a Single-Point Acoustic Doppler Current Sensor Mounted on a TABS II Spar Buoy. Proceedings from MTS/IEEE Oceans 2000 Conference, September 11-14, 2000, Providence, RI. [5] Walpert, J.N., N.L. Guinasso, Jr., and L.L. Lee, III. A New Generation of TABS II Buoy for the Texas Automated Buoy System (TABS). Proceedings from MTS/IEEE Oceans 2005, September 18-21, 2005, Boston, MA.. V. FUTURE PLANS Testing of these two prototypes will continue through the end of 2009, and will include deployment of the buoys in the Offshore Technology Research Center wave tank to test the actual period response of the hull and mooring, and a full term deployment during a TABS cruise. GERG plans on building an additional two buoys during 2009/2010 and incorporating revisions based on testing done so far. One goal is to reduce the weight of the buoy from 150 pounds to approximately 135 pounds. Methods of streamlining and reducing the cost associated with fabricating the buoy will be examined. A review of the software will be conducted and suitable recommendations for changes will be incorporated. Acknowledgments GERG gratefully acknowledges the continued support from the Texas General Lands Office, and in particular Dr. Robert (Buzz) Martin for his unwavering encouragement and support. References [1] Martin, R.D, Jr., N. L. Guinasso, L.L. Lee III, J.N. Walpert, L.C. Bender, R.D. Hetland, S.K. Baum, M.K. Howard (2005). Ten Years of Realtime, Near-Surface Current Observations Supporting Oil Spill Response. Proceedings, 2005 International Oil Spill Conference. American Petroleum Institute, Washington, DC. pp [2] Kelly, F.J., N.L. Guinasso, Jr., L.L. Lee III, G.F. Chaplin, B.A. Magnell, and R.D. Martin, Jr., 1998: Texas Automated Buoy System (TABS): A public resource. Proceedings of the Oceanology International 98 Exhibition and Conference, March 1998, Brighton UK, Vol. 1, pp [3] Walpert, J.N., N.L. Guinasso, Jr., and L.L. Lee, III. High Speed Two Way Data Communications Used in the Texas Automated Buoy System (TABS). Proceedings from MTS/IEEE Oceans 2002, October 29-31, 2002 Biloxi, MS.