William J. Kirkwood

Deep-ocean field test of methane hydrate formation from a remotely operated vehicle

We have observed the process of formation of clathrate hydrates of methane in experiments conducted on the remotely operated vehicle (ROV) Ventana in the deep waters of Monterey Bay. A tank of methane gas, acrylic tubes containing seawater, and seawater plus various types of sediment were carried down on Ventana to a depth of 910 m where methane gas was injected at the base of the acrylic tubes by bubble stream. Prior calculations had shown that the local hydrographic conditions gave an upper limit of 525 m for the P-T boundary defining methane hydrate formation or dissociation at this site, and thus our experiment took place well within the stability range for this reaction to occur. Hydrate formation in free seawater occurred within minutes as a buoyant mass of translucent hydrate formed at the gas-water interface. In a coarse sand matrix the filling of the pore spaces with hydrate turned the sand column into a solidified block, which gas pressure soon lifted and ruptured. In a fine-grained black mud the gas flow carved out flow channels, the walls of which became coated and then filled with hydrate in larger discrete masses. Our experiment shows that hydrate formation is rapid in natural seawater, that sediment type strongly influences the patterns of hydrate formation, and that the use of ROV technologies permits the synthesis of large amounts of hydrate material in natural systems under a variety of conditions so that fundamental research on the stability and growth of these substances is possible.

Development of the DORADO mapping vehicle for multibeam, subbottom, and sidescan science missions

Oceanographic science is frequently hindered by a lack of spatial and temporal resolution for most parameters oceanographic science desires to measure. This paper discusses our effort to advance the current state of bathymetric mapping as part of the Monterey Bay Aquarium Research Institute (MBARI) charter. MBARI scientists and engineers, in consultation with the external community, have produced a new multibeam mapping autonomous underwater vehicle (AUV) system. The system is intended to reduce some of the impediments encountered by science trying to resolve specific portions of the oceans bottom. Starting with the established and in-house developed Dorado AUV technology, MBARI engineering refined the AUV into a full ocean depth capable and now operational multibeam mapping system (MBAUV). The MBAUV system conducts regular multibeam bathymetry, subbottom, and sidescan surveys for oceanographic science. MBAUV is a torpedo-shaped, 6000 m rated vehicle operating the aforementioned sonars simultaneously. The endurance of the MBAUV is approximately 8 h at 3 kn and is designed to support 16 h operations at 3 kn by adding an additional battery section. This paper describes the basics of the MBAUV and our design trades and modifications to the Dorado AUV in support of multibeam mapping missions. The paper also reviews a sampling of the results from a series of missions that demonstrate the performance of various subsystems and the science quality data available from the MBAUV.

A Review of Advances in Deep-Ocean Raman Spectroscopy

We review the rapid progress made in the applications of Raman spectroscopy to deep-ocean science. This is made possible by deployment of instrumentation on remotely operated vehicles used for providing power and data flow and for precise positioning on targets of interest. Early prototype systems have now been replaced by compact and robust units that have been deployed well over 100 times on an expeditionary basis over a very wide range of ocean depths without failure. Real-time access to the spectra obtained in the vehicle control room allows for expedition decision making. Quantification of some of the solutes in seawater or pore waters observed in the spectra is made possible by self-referencing to the ubiquitous m2 water bending peak. The applications include detection of the structure and composition of complex thermogenic gas hydrates both occurring naturally on the sea floor and in controlled sea floor experiments designed to simulate the growth of such natural systems. New developments in the ability to probe the chemistry of sediment pore waters in situ, long thought impossible candidates for Raman study due to fluorescence observed in recovered samples, have occurred. This permits accurate measurement of the abundance of dissolved methane and sulfide in sediment pore waters. In areas where a high gas flux is observed coming out of the sediments a difference of about ×30 between in situ Raman measurement and the quantity observed in recovered cores has been found. New applications under development include the ability to address deep-sea biological processes and the ability to survey the sea floor chemical conditions associated with potential sub-sea geologic CO2 disposal in abandoned oil and gas fields.

Reliability growth of autonomous underwater vehicle-Dorado

Underwater environments are highly unstructured, uncertain, and dynamic. However, over the past three decades many autonomous underwater vehicles (AUVs) have been developed and successfully deployed for various oceanographic applications. There is a growing need for the AUVs to be reliable for collecting useful data and samples for their users. An AUV is a typical one-of-a-kind product for which it is difficult to derive a mathematical/statistical model for reliability prediction. The failure modes effects and criticality analysis (FMECA) can produce more effective results. However, the assessment of reliability growth of an AUV is very important for predicting its operational success in challenging underwater environments. In this paper, we present the identification of different types of failures that occurred during the past one and a half years of operation of MBARIs Dorado AUV, classification of those failures, and the reliability growth analysis for the vehicle. Reliability issues of various subsystems and operational procedure of the AUV have also been discussed. An extensive analysis of operational data and test results are presented in this paper.

Field operation of a robotic small waterplane area twin hull boat for shallow-water bathymetric characterization

An innovative robotic boat has been developed for performing bathymetric mapping of very shallow coastal, estuarine, and inland waters. The boat uses a small waterplane area twin hull design to provide natural platform stability for a multibeam sonar payload, and a navigation system automatically guides the boat in a “lawn-mowing” pattern to map a region of interest. Developed in stages over five years as part of a low-cost student design program, the boat is now operational and is being used to generate science-quality maps for scientific and civil use; it is also being used as a testbed for evaluating the platform for other types of scientific missions and for demonstrating advanced control techniques. This paper reviews the student-based development process, describes the design of the boat, presents results from field operations, and reviews plans for future extensions to the system.

Mapping payload development for MBARI's Dorado-class AUVs

The Monterey Bay Aquarium Research Institute (MBARI) is developing an autonomous seafloor mapping capability for deep ocean science applications. The MBARI Mapping AUV is a 0.53 m (21 in) diameter, 5.1 m (16.7 ft) long, Dorado-class vehicle designed to carry four mapping sonars. The primary sensor is a 200 kHz multibeam sonar producing swath bathymetry and sidescan. In addition, the vehicle carries 100 kHz and 410 kHz chirp sidescan sonars, and a 2-16 kHz sweep chirp subbottom profiler. Navigation and attitude data are obtained from an inertial navigation system (INS) incorporating a ring laser gyro and a 300 kHz Doppler velocity log (DVL). The vehicle also includes acoustic modem, ultra-short baseline navigation, and long-baseline navigation systems. A single cylindrical pressure housing contains all of the mapping sonar electronics, and the main vehicle control and acoustic communications electronics are housed in a separate glass ball. The Mapping AUV is powered by three 2 kWhr Li-polymer batteries, providing an expected mission duration of 12 hours at a typical speed of 1.5 m/s. The assembled package is rated to 6000 m depth, allowing MBARI to conduct high-resolution mapping of the deep-ocean seafloor. Initial at-sea testing commenced in May 2004 using the subbottom profiler and 100 kHz sidescan. The sonar package will also be mountable on ROV Ventana, allowing surveys at altitudes < 10 m at topographically challenging sites. The MBARI Seafloor Mapping team is now working towards integration of the multibeam sonar and towards achieving regular operations during 2005.

Creating Controlled CO 2 Perturbation Experiments on the Seafloor - Development of FOCE Techniques

Experimental recent progress on the design and testing of systems for carrying out controlled CO₂ perturbation experiments on the sea floor with the goal of simulating the conditions of a future high CO₂ world. Controlled CO₂ enrichment (FACE) experiments have long been carried out on land to investigate the effects of elevated atmospheric CO₂ levels on vegetation, but only limited work on CO₂ enrichment on enclosed systems has yet been carried out in the ocean. With rising concern over the impacts of ocean acidification on marine life there is a need for greatly improved techniques for carrying out in situ experiments, which can create a DeltapH of 0.3 to 0.5 by addition of CO₂, on natural ecosystems such as coral reefs, cold water corals, and other sensitive benthic habitats. This is no easy task. Unlike land based experiments where simple mixing in air is all that is required, CO₂ has complex chemistry in seawater with significantly slow reaction kinetics. Scientists must design systems to take this into account. The net result of adding a small quantity of CO₂ to sea water is to reduce the concentration of dissolved carbonate ion, and increase bicarbonate ion through the following reaction:CO₂+H₂O+CO₃^2- -> 2HCO₃ In practice the reaction between CO₂ and H₂O is slow and is a complex function of temperature, pH, and TCO₂, with the reaction proceeding more rapidly at lower pH and higher temperatures. Marine animals in the natural ocean will typically experience only small and temporary shifts from environmental CO₂ equilibrium. Valid perturbation experiments must try to expose an experimental region to a stable lower pH condition, and avoid large and rapid pH variability. The most common sensor used for experimental control is the pH electrode, and this detects only H+ ion, not any of the dissolved CO₂ species. We first explored the reaction kinetics of a CO₂ perturbation in a series of closed loop pH cell experiments carried out at various depths under ROV control. These were found to be well matched to the Zeebe & Wolf-Gladrow [1] model. From these results, functions for the delay time required for equilibrium were devised and a design for a delay loop to achieve at least 2 e-folding times between CO₂ injection and animal exposure was developed. We tested this prototype system in October 2007 in a series of ROV controlled experiments at a depth of 1000 meters. The working fluid used for enrichment was surface sea water saturated at one atmosphere with pure CO₂ gas to create a solution of about pH 4.8 and 56 mM total CO₂. This was carried to depth in a 56 liter piston accumulator, and dispensed as needed into a flexible polyethylene bag for subsequent addition into the experimental unit. The design consisted of a 4 meter delay loop leading to a control volume (square box, 25 cm per side) outfitted with three pH electrodes and a CTD. To determine the uniformity of the pH, two pH electrodes were positioned in the control volume and a third electrode was positioned just beyond the control volume in the flow stream. Ambient seawater, pumped at a desired rate with a modified thruster, was mixed at the beginning of the delay loop with controlled continuous injection of the CO₂-rich working fluid in a ratio typically of about 2001 depending on the pH perturbation desired. For these initial tests, a feed-forward system was used where flow rates of both the ambient seawater and CO₂-rich seawater were varied to produce a desired pH change. Future designs will incorporate a feedback loop to allow for automated precision pH control. These field tests were successful in showing that a plume of lower pH seawater could be accurately created and maintained in the deep ocean. The pH was reduced by up to 0.9 pH units from the ambient value of 7.8 covering well beyond the range of projected ocean pH scenarios for the next century. Near future goals will involve use of the MARS undersea cable recently deployed in Monterey Bay, California for power, communication and control, and a long-term experiment will be performed to demonstrate the operational feasibility of this technology for ocean acidification studies worldwide.pH electrodes and a CTD. To determine the uniformity of the pH, two pH electrodes were positioned in the control volume and a third electrode was positioned just beyond the control volume in the flow stream. Ambient seawater, pumped at a desired rate with a modified thruster, was mixed at the beginning of the delay loop with controlled continuous injection of the CO2-rich working fluid in a ratio typically of about 200:1 depending on the pH perturbation desired. For these initial tests, a feed-forward system was used where flow rates of both the ambient seawater and CO2-rich seawater were varied to produce a desired pH change. Future designs will incorporate a feedback loop to allow for automated precision pH control. These field tests were successful in showing that a plume of lower pH seawater could be accurately created and maintained in the deep ocean. The pH was reduced by up to 0.9 pH units from the ambient value of 7.8 covering well beyond the range of projected ocean pH scenarios for the next century. Near future goals will involve use of the MARS undersea cable recently deployed in Monterey Bay, California for power, communication and control, and a long-term experiment will be performed to demonstrate the operational feasibility of this technology for ocean acidification studies worldwide.

T1 - AUV Technology and Application Basics

AUV Application Basics is a short course that provides an overview of current AUV technologies and operations. The objective is to establish a basic understanding of what currently available AUV systems can provide and best practices in use. The class is targeted at scientists interested in using AUVs for oceanographic applications. The attendee will gain basic understanding of AUV types, technologies, terminology, and navigation techniques, including discussion of the comparative strengths of AUVs and alternative methods of data collection. The attendee will also be provided an understanding of tradeoffs in AUV operations, including power estimation, endurance considerations, and mission structure to acquire the desired data sets. Key points are illustrated by applications and results from the Monterey Bay Aquarium Research Institutes (MBARI) Dorado AUV and other AUV operations. Topics include: Basic AUV technology, AUV at-sea Operation, Payload Considerations, Mission Planning, Upper and Mid-Water AUV missions, Benthic and Mapping AUV missions, Data Collection and Reduction, AUV Integration into Sampling Networks, and a look at coming AUV advances. The interactive format, using the materials provided, allows the attendee discussion time for relevance and demonstration purposes regarding real or potential AUV plans.AUV Application Basics is a short course that provides an overview of current AUV technologies and operations. The objective is to establish a basic understanding of what currently available AUV systems can provide and best practices in use. The class is targeted at scientists interested in using AUVs for oceanographic applications. The attendee will gain basic understanding of AUV types, technologies, terminology, and navigation techniques, including discussion of the comparative strengths of AUVs and alternative methods of data collection. The attendee will also be provided an understanding of tradeoffs in AUV operations, including power estimation, endurance considerations, and mission structure to acquire the desired data sets. Key points are illustrated by applications and results from the Monterey Bay Aquarium Research Institutes (MBARI) Dorado AUV and other AUV operations. Topics include: Basic AUV technology, AUV at-sea Operation, Payload Considerations, Mission Planning, Upper and Mid-Water AUV missions, Benthic and Mapping AUV missions, Data Collection and Reduction, AUV Integration into Sampling Networks, and a look at coming AUV advances. The interactive format, using the materials provided, allows the attendee discussion time for relevance and demonstration purposes regarding real or potential AUV plans.

SeaWASP: A Small Waterplane Area Twin Hull Autonomous Platform for Shallow Water Mapping

Students with Santa Clara University (SCU) and the Monterey Bay Aquarium Research Institute (MBARI) are developing an innovative platform for shallow water bathymetry. Bathymetry data is used to analyze the geography, ecosystem, and health of marine habitats. However, current methods for shallow water measurements typically involve large, manned vessels. These vessels may pose a danger to themselves and the environment in shallow, semi-navigable waters. Small vessels, however, are prone to disturbance by the waves, tides, and currents of shallow water. The SCU / MBARI autonomous surface vessel (ASV) is designed to operate safely, stably in waters > 1 m and without significant manned support. Final deployment will be at NOAAs Kasitsna Bay Laboratory in Alaska. The ASV utilizes several key design components to provide stability, shallow draft, and long-duration unmanned operations. Bathymetry is measured with a multibeam sonar in concert with DVL and GPS sensors. Pitch, roll, and heave are minimized by a Small Waterplane Area Twin Hull (SWATH) design. The SWATH has a submerged hull, small water-plane area, and high mass to damping ratio, making it less prone to disturbance and ideal for accurate data collection. Precision sensing and actuation is controlled by onboard autonomous algorithms. Autonomous navigation increases the quality of the data collection and reduces the necessity for continuous manning. The vessel has been operated successfully in several open water test environments, including Elkhorn Slough, CA, Stevens Creek, CA, and Lake Tahoe, NV. It is currently is in the final stages of integration and test for its first major science mission at Orcas Island, San Juan Islands, WA, in August, 2008. The Orcas Island deployment will feature design upgrades implemented in Summer, 2008, including additional batteries for all-day power (minimum eight hours), active ballast, real-time data monitoring, updated autonomous control electronics and software, and data editing using in-house bathymetry mapping software, MB-System. This paper will present the results of the Orcas Island mission and evaluate possible design changes for Alaska. Also, we will include a discussion of our shallow water bathymetry design considerations and a technical overview of the subsystems and previous test results. The ASV has been developed in partnership with Santa Clara University, the Monterey Bay Aquarium Research Institute, the University of Alaska Fairbanks, and NOAAs West Coat and Polar Regions Undersea Research Center.

Development and initial testing of a SWATH boat for shallow-water bathymetry

Students at Santa Clara University have developed a SWATH boat prototype capable of shallow water operation and configured for creating bathymetric maps through the use of a multi-beam sonar. The sonar works in concert with DVL and precision GPS sensors in order to log data that can be used to generate bathymetric maps through the use of the MB System software suite. The boats physical structure includes pontoons, vertical supports, and a platform housing the vessels power, sensor, control, and communication systems. Additional systems include a camera and video transmission system for remotely piloted operation, a suite of sensors and controllers for autonomous navigation, and equipment for ballasting the pontoons. An off-board control station aids in navigation computations, provides the pilot/supervisor interface, and links the system to the internet for real-time internet-based piloting and/or monitoring of the mission. An additional winch system has been developed for future operations involving the deployment of a sensor package to various depths. A number of successful test deployments have been completed to date, and operations during the summer of 2008 will include mapping of the Elkhorn Slough, portions of the southern end of San Francisco Bay, portions of Lake Tahoe, and shallow water coastal waters in the San Juan Islands. Ultimately, a more robust model of the boat is planned for deployment at NOAAs Kasitsna Bay Laboratory in Alaska. The system has been developed in partnership with the Monterey Bay Aquarium Research Institute, the University of Alaska Fairbanks, and NOAAs West Coast and Polar Regions Undersea Research Center. This paper will review the technical design of the system and will present the functional performance achieved to date.