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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE Other Requirements for Establishing a Seafloor Observatory Network At present, the technology exists to establish a network of both cabled and moored seafloor observatories. This technology includes satellite telemetry, mooring technology, undersea cable technology, and observatory-deployment technology. There will obviously be major improvements in these capabilities and their cost effectiveness, but at present they are sufficiently advanced for general use. As discussed below, many long-term sensors and instruments are also currently available for observatory use (e.g., thermistors, conductivity meters). On the other hand, some sensors are available in basic form, but will need improvements for long-term deployment (e.g., water-particle samplers); whereas others will need major design and development (e.g., many chemical and biological sensors and gene chips). Advances in Autonomous Underwater Vehicles (AUV) technology are also essential for the success of an observatory network. This chapter outlines currently available technology and future developments needed to establish both moored and cabled observatories. SENSOR TECHNOLOGY While there are a wide variety of sensors available for undersea research, and there are many key instruments that are being deployed for long time periods (such as , hydrophone arrays, and current meters), it is clear that development of new sensors will be a critical need in order for observatories to be fully effective. Sensor technology, particularly in chemistry and biology, is not sufficiently advanced to take optimal advantage of the ocean observatory infrastructure. In addition, enhancements need to be made before existing sensors can be expected to operate unattended for long periods of time in an observatory setting. If an ocean observatory infrastructure
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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE is to be established, a substantial parallel investment in sensor technology will be necessary. CURRENTLY AVAILABLE TECHNOLOGY Sensors currently available for deployment in a seafloor observatory setting include those for basic physical measurements (temperature, pressure, turbulence, optical clarity, current velocity, wind speed, wave height, seismicity, acoustics, magnetics, gravity), measurements of water properties (conductivity, oxygen, nutrients, dissolved gasses, analysis of suspended particles), and biological measurements (fluorescence, video plankton recorders, hydrophones for ambient noise, acoustic sensors for detection of biota, and gene chips1). There are also several types of samplers available for the collection of fluids and biological samples that require shore-based analysis. Many of these sensors and samplers, however, are not presently suitable for long-term deployment for a variety of reasons, such as the need for frequent servicing, instability of chemical reagents, sensitivity to biofouling, or intolerance to high temperatures (for example, there are currently only a handful of properties [temperature, pH, H2S]) that can be measured in 300°C hydrothermal fluid). Thus, the properties of most high-temperature hydrothermal fluids are presently determined by laboratory analysis of samples after they have cooled. Biofouling is another problem that affects almost all seafloor instrumentation and is especially severe with video cameras, pumps, and other instruments deployed at hydrothermal sites. In each of the research disciplines, there are certain “basic” sensors that are considered so critical or common that the observatory should supply them as part of the standard infrastructure. At coastal observatories (see Chapter 2, section titled “Coastal Ocean Processes”), these include sensors for basic meteorological conditions (wind speed, air temperature, air pressure); for ocean surface conditions (current velocity, wave height, turbulence); and for water column conditions (temperature, conductivity, nitrate, dissolved gases, pH, gene chip, plankton recorder, water sampler, fluorometer, acoustic fish-tag trackers). For the deep ocean (see Chapter 2, sections titled “Role of the Ocean in Climate,” “Turbulent Mixing and Biophysical Interaction,” and “Ecosystem Dynamics and Biodiversity”), many critical water-column measurements are similar to those for coastal regions, but they also include sensors for pressure and horizontal electric field, inverted echo sounders, hydrophones, and bioacoustic profilers. In the case of benthic experiments (see Chapter 2, sections titled “Fluids and Life in the Oceanic Crust” and 1 Although gene chip technology currently exists, it will need significant refinement to be suitable for wide use in oceanographic research.
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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE “Ecosystem Dynamics and Biodiversity”), the most important tool would consist of an AUV equipped with a variety of instruments for imaging the seafloor and collecting samples, including a laser line scanner or sonar system for topography, an imaging scanner for organic matter, in situ sediment sample processing for basic physical parameters, and an acoustic sediment profiler. Other critical benthic instrumentation includes acoustic benthic boundary layer profilers and settlement plates and corers for faunal recruitment studies. At vents, boreholes, and seeps (see Chapter 2, section “Fluids and Life in the Oceanic Crust”), critical instrumentation include those for physical measurements (temperature, fluid flow rate, currents, pressure), for in situ chemical and biological measurements, and for sample collection (osmotic pump samplers, gas-tight samplers, particle samplers). At geophysical seafloor stations (see Chapter 2, section “Dynamics of Oceanic Lithosphere and Imaging Earth's Interior”), basic sensors would include three-component broadband seismometers, hydrophones, magnetometers, absolute pressure transducers, and geodetic sensors for measuring tilt and deformation. FUTURE DEVELOPMENTS NEEDED For the full potential of seafloor observatories to be realized, new and innovative seafloor instruments must be developed. Although it is difficult to predict which research areas will give rise to new sensors, there are certain areas where this development is essential. In particular, biological and chemical sensor development lags behind that for physical sensors. Thus, to maximize the potential for biological and chemical research at a seafloor observatory network, sensor development needs to be a high priority. Sensors that are commonly used only in laboratory settings will require substantial development before these instruments can make accurate measurements while being left unattended for long periods of time. Sensors are also needed that are immune to high temperatures, high pressures, corrosive conditions, biofouling, and other extreme environments found on the seafloor. Furthermore, there is a general need for development of the following: sensors to measure flow rates in high-temperature fluids, advanced sensors deployment for boreholes (downhole logging), instruments for the collection of water samples over extended periods (such as osmosamplers), instruments to collect improved geodetic measurements, and instruments and techniques for the burial and borehole emplacement of broadband seismic sensors. Considerable development is also needed in the area of ocean acoustics for observatory applications. Hydrophone arrays, such as the SOund SUrveillance System (SOSUS) have been extremely effective at detecting seafloor volcanic and tectonic events and allowing a timely response to these events. Thus, it is recommended that the existing SOSUS arrays be main
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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE tained if at all possible and that new relocatable hydrophone systems be developed to augment the fixed SOSUS hydrophones. An important component of the design phase of an observatory network will be the development of specifications for interfaces between the observatory node and instruments and sensors. These specifications include standardized direct-current (DC) voltages and power control conventions, a layered set of communications protocols using conventional networking standards, and standardized connectors and pin configurations. Standards on allowable environmental effects also need to be established to minimize the impact of an individual instrument or sensor on other observatory experiments. In addition, as part of an observatory network, a certified testing capability will be needed to test instrumentation and identify potential interference problems. POWER GENERATION TECHNOLOGY CURRENTLY AVAILABLE TECHNOLOGY As described previously, the power requirements for a moored-buoy observatory span a range of a few 10s of watts up to several kW. A 50 W output can be achieved with solar or wind power generation, or both, coupled to rechargeable batteries. Power generation above 50 W can be realized using a diesel generator similar to those operating in Coast Guard Large Navigational Buoys (LNB) (Dewey, 1974). The latter approach will obviously entail periodic refueling. Projected power requirements for cabled observatories are anticipated to be 2-20 kW per node. Currently, high-power DC-generation equipment used in commercial cable systems have the capability to provide on the order of 10 kW at approximately 10 kV and 1 A. FUTURE DEVELOPMENTS NEEDED For a cabled observatory, significant engineering development will be necessary to provide more than a few kW of power. If the network requires more than approximately 10 kW per shore station, new DC power-generation equipment will be needed. This could be an expensive undertaking because of the limited number of vendors of such equipment and the critical safety concerns. Another consideration is that the power transmission schemes used in the subsea telecommunications industry may not be adequate for a cabled observatory with many nodes. Consequently, power schemes based on existing land-based systems may need to be adopted. The following developments to seafloor power hardware will be required: The current design of specific DC conversion hardware will have to be
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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE altered to obtain the required reliability. Engineering this change should be a relatively inexpensive but essential activity. To provide a workable thermal environment for the power conditioning, network management and science-experiment management equipment, the physical design of the thermal paths from the electronics to seawater need to be carefully engineered. To meet the necessary thermal specifications, significant trade-offs will have to be made between the use of commercially available equipment and that which is purposely built in order to achieve operational requirements for system operational time (versus downtime), repair cost, and lifetime. The observatory physical power path will need to be designed to minimize the probability and effects of corona.2 The elimination of potential corona generation sites will require careful attention to specifics of the power generation hardware. In addition, the susceptibility of network management and science experiment equipment to corona noise will need to be examined. The configuration and hardware for power surge protection need to be designed to provide a fault-tolerant observatory network. It must be assumed that there will be cable and other equipment failures that will produce significant power surges resulting from the interruption of the DC path. If the observatory nodes are not properly protected, there is potential for these surges to seriously damage the node electronics. The development of a surge protection configuraton will require careful computer modeling and simulation of the various fault scenarios. These scenarios could be quite complex for an observatory with many nodes and more than one shore station. Computer simulations will also provide input to the design of the appropriate voltage ramp-up and ramp-down sequences. There is potential for simulation and analysis tools from terrestrial systems to be adopted for these purposes. TECHNOLOGICAL ADVANCES IN DATA TELEMETRY TECHNOLOGY CURRENTLY AVAILABLE TECHNOLOGY Moored-buoy observatories will depend on commercially available satellite communication systems to telemeter data from the buoy back to shore. The satellite communications industry is currently undergoing rapid change as part of the worldwide explosion in wireless communication. The communi 2 Corona (discharge) - an electrical discharge accompanied by ionization of surrounding atmosphere [syn: corona, corposant, St. Elmo's fire, Saint Elmo's fire, Saint Elmo's light, Saint Ulmo's fire, Saint Ulmo's light, electric glow].
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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE cation rates and tariffs supported by some current and proposed satellite systems are shown in Table 4-1. There are, in addition to global systems (Table 4-1), a number of regional satellite systems that may be capable of providing service to ocean areas, particularly those close to shore. At present, the only global systems in operation that can provide the high bandwidth needed for continuous data transmission are INMARSAT-B and C-Band (Table 4-1). A limitation of these two systems is that they require the gyrostabilized antenna on the buoy to be pointed with an accuracy of a fraction of a degree. This results in substantial power consumption. Such a system could be mounted on either a disk or spar buoy, but for full-time operation of the satellite telemetry system, the power requirements would necessitate the use of a diesel generator. In addition, tariffs for global coverage are high, making continuous, real-time data telemetry prohibitively expensive. Currently, the only economically viable option for continuous telemetry is to lease time on a C-Band commercial satellite. It appears likely that, within a few years, there will be operational systems that will be competitive with C-Band and INMARSAT-B in terms of communication rates and possibly superior in terms of power and antenna steering TABLE 4-1 Specifications for Current and Proposed Global Communications Satellites SYSTEM INMARSAT-Ba TELEDESIC GLOBALSTAR C-BAND Service types Voice, fax, data Voice, faxb, datab Voice, fax, data Data Data Rate 64 kbit/s 64 kbit/s to 2 Mbit/s 9.6 kbit/s 19.2 kbit/s-2 Mbit/s Tariff $7/min $15/Mbyte Unknown $1.50-$3.00/minc $20-$40/Mbyte $5K/month/128kbit/sd $0.015/Mbyte Service scheduled In service Under development Q4 2000 In service aTariff would likely be lower for continuous service; the system is presently designed to serve as a dialup resource. bFax and data service not yet offered. cService in oceanic areas will be limited, as there must be a gateway within the footprint of a single low Earth orbit satellite. dObtained by leasing segments from providers, such as INTELSAT, PANAMSAT, and Palapa C1. The segment can be time multiplexed between buoys to reduce overall costs.
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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE TABLE 4-2 Low-Speed Communications Satellites SYSTEM INMARSAT-M ORBCOMM Service types Data Data Data Rate 2.4 kbit/s 2.4 kbit/s Tariff $3/min $167/Mbyte $10 kbit/s $10K/Mbyte Service scheduled In service In service requirements (e.g. TELEDESIC). While satellite systems now online or coming online (e.g., GLOBALSTAR) do not have the communication rate capabilities of INMARSAT or INTELSAT (or other dedicated commercial systems), they do have the advantage of requiring only an omnidirectional antenna for data transfer speeds as high as 64 kb/s. The power requirements of these “new-generation” satellite communication systems are projected to be modest (e.g., 14 W transmit; 4.5 W receive), and they will have the capacity to telemeter a substantial subset of observatory data at an acceptable cost. In addition to higher data rate systems, there are currently lower-speed, low-power satellite systems available for communications and telemetry (Table 4-2). These could be used for applications, such as ARGO, that do not require high telemetry data rates, or as a backup system for a moored buoy. FUTURE DEVELOPMENTS NEEDED The satellite communications industry is currently undergoing rapid change, and the systems that will be available in 3 or 5 years are difficult to predict. Market forces outside the academic community will drive the pace of technical development in this industry. The availability of “new generation” communications systems with low-power, omni-directional antennas and data telemetry rates comparable or superior to current INMARSAT-B or C-Band satellites would make it feasible to design smaller, lighter, lower-cost, moored-buoy systems. It is, however, not certain whether commercial systems will have adequate coverage in areas of scientific interest. If competition with other wireless communication systems reduces tariffs, continuous telemetry at relatively high data-transfer rates may become cost-effective. Given the uncertainty in this rapidly changing industry, the development strategy for moored-buoy observatories should remain flexible.
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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE AUTONOMOUS UNDERWATER VEHICLE TECHNOLOGY FOR SEAFLOOR OBSERVATORIES AUVs have the potential to undertake a variety of mapping and sampling missions while using fixed observatory installations to recharge batteries, offload data, and receive new instructions (Box 4-1). A principle use for AUVs will be to map seafloor and water-column properties and to document horizontal BOX 4-1 AUTONOMOUS OCEAN-SAMPLING NETWORKS Objective: Autonomous Ocean-Sampling Networks (AOSN) are a class of relocatable observatory in which mobile platforms supported by a communications network provide a nested observational capability. This program has developed a significant fraction of the technologies that in the future could support the inclusion of Autonomous Underwater Vehicles (AUVs) in ocean observatories. The AOSN utilize small, high-performance AUVs to provide platforms for a wide range of sensors and sampling systems. These vehicles operate at 3-4 knots for periods on the order of half a day. Docking stations are being developed to provide long-term deployments of these AUVs. Buoyancy-driven vehicles (gliders) operate at speeds less than a knot for a period of several months, carrying a minimal oceanographic sensor suite. Because such vehicles are less expensive, they can be employed in greater numbers to provide a synoptic picture of an ocean region. Development of acoustic communications has been a major objective, to allow real-time control of AUVs and other enabling capabilities, such as adaptive sampling. A multi-institutional effort led by the Massachusetts Institute of Technology has employed a mooring with a docking station and two-way satellite communications capabilities in tests of a relocatable AOSN. Furthermore, the Office of Naval Research (ONR) and Naval Oceanographic Office support for AUV operations at the Long-term Ecosystem Underwater Observatory (LEO-15) (Box 2-10) has demonstrated the utility of AUV operations at a cabled observatory. Results: Although primarily an engineering-development program, a number of successful AOSN deployments have been demonstrated. Specific elements, such as some acoustic systems and AUV designs, have been licensed to industry and are commercially available.
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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE variability, which is necessary for establishing the context of point-like measurements made from fixed instrumentation. Another use of AUVs will be to extend the spatial observational capability of seafloor observatories. Many oceanographic processes occur episodically, in relatively localized regions. For example, eruptions at spreading ridges may result in the creation of square kilometers of seafloor, but these events may only be indirectly detectable at a mooring tens of kilometers away. AUVs provide a method by which an observatory can deliver instruments to sites of interest, thus greatly expanding the region of coverage. Scenarios for employing AUVs as elements of seafloor observatories envision small vehicles, weighing at most a few hundred kilograms, with docking capabilities. Docking capabilities are necessitated by the limited endurance of present AUVs, which have typical mission lengths on the order of a day or less. Vehicle endurance is dictated by survey speeds (typically about 5 km/hr) and power consumption by onboard computers and sensors, which can range up to hundreds of watts depending on the payload. The docking capability thus provides the means to extend the AUV presence in the ocean, while at the same time retaining the ability to retrieve data and exert control over AUV missions. Docking also provides a safe parking location for an AUV between activities. General goals of AUV missions include the following: Seafloor mapping—AUVs are capable of operating much closer to the seafloor than most other survey systems; therefore, they can collect high-resolution, high-accuracy mapping data, in addition to other geophysical parameters, such as bathymetry and magnetics. Water-column mapping—AUVs provide the capability to map physical and chemical parameters horizontally by flying a grid at a constant depth, vertically by flying a yo-yo pattern, or in three-dimensions (3-D) by combining vertical and horizontal patterns. Repeated 3-D surveys of an AUV in a given volume enables the production of a 4-D dataset. Measuring fluxes—Many scientific questions require measurements of the transport of energy, inorganic and organic matter, or dissolved chemical species via a wide range of mechanisms. AUVs provide this capability at specific locations near an observatory node. Initializing and constraining models—Real-time nowcast and forecast systems for physical parameters (e.g., temperature, salinity, currents) can be useful for a wide range of oceanographic studies. AUVs are capable of obtaining the spatially separated physical measurements needed to initialize and constrain such models.
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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE While AUVs have been employed for oceanographic purposes since the mid-1960s, it is only in the last several years that they have begun to be adopted by the academic oceanographic community. As with Remotely Operated Vehicles (ROVs) in the early 1980s, AUVs are becoming more reliable, and are proving to be useful for a variety of applications. Thus, specific capabilities for AUVs in scientific research are becoming clear. Over the next decade, we can anticipate continuous improvements in endurance, sensing capabilities, navigational infrastructure, communications, and intelligent control of these vehicles. Existing AUVs exhibit variations in weight of four orders of magnitude, from 10 to 10,000 kg dry weight. However, most U.S. oceanographic efforts are focused on vehicles at the low end of this scale, with most vehicles weighing less than a few hundred kilograms. Although a fuel-cell-powered vehicle with an endurance of up to two weeks is in development, the endurance of a typical AUV is on the order of half a day at speeds of approximately 5 km/hr. A variety of instruments have been used on AUVs, including those to measure conductivity, temperature, and depth (CTD); optical water-quality sensors; turbulence; and current strength and direction (Acoustic Doppler Current Profilers). In addition, still and video cameras, multibeam echo sounders, sidescan sonar, and laser line-scan imagers have also been mounted on AUVs. (NRC, 1996b) There is an emerging class of AUVs with very long endurance that propel themselves by modulating buoyancy and translating vertical into forward motion through lifting surfaces. These vehicles, commonly referred to as gliders, operate at speeds on the order of 1 km/hr with minimal payloads, to obtain an endurance of many months. The first multi-day glider deployment in the ocean occurred in 1999. Since this deployment, glider capabilities have been progressing rapidly. For the purposes of this report, however, gliders are considered complementary rather than integral to seafloor observatories. Seafloor observatories will place significant navigation demands on AUVs, but they also could provide an unparalleled navigation infrastructure to support AUV operations. A common navigation technique used in the deep ocean is long-baseline acoustic navigation. Long-baseline navigation employs arrays of bottom-mounted transponders operating at frequencies from 7 to 15 kHz to provide locations with a potential accuracy of several meters. Since transponders are typically placed no further than twice the water depth apart, and much closer for high-performance navigation, it is unusual to provide coverage for areas more than 10 kilometers. The extensive use of such an array, as would be required with repeated AUV operations in a defined area, would likely encourage the deployment of large numbers of transponders for accurate wide-area coverage despite the costs this level of detail would entail. Variations include using lower frequencies to achieve larger separations between transponders, usually at the expense of accuracy and update rate, and using arrays of hydrophones to track acoustic sources as is done at U.S. Navy
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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE tracking ranges. The prospect of spatially distributed, electrically connected on the seafloor provides opportunities for innovative acoustic navigation techniques that might take advantage of this unusual arrangement. Another navigation capability for AUV uses inertial and Doppler velocity-log sensors to provide an accurate dead-reckoning capability. Military systems have demonstrated navigation accuracy better than 0.1 percent of distance traveled. The full suite of such sensors and navigation algorithms are expensive and power-consumptive, on the order of hundreds of thousands of dollars and one hundred watts, respectively. However, substantial commercial pressure for this capability promises to deliver more reasonably priced systems with military-level performance and lower power consumption within the time frame of ocean observatories. One problem with this technique is that the AUV must remain sufficiently close to the seafloor for the Doppler velocity log to have bottom lock—a few hundred meters for current systems on the small vehicles discussed here. A correlation velocity log can provide a similar function to the Doppler velocity log at distances much greater from the bottom; however, such systems are not readily available commercially. A final problem with dead-reckoning is that navigation errors are unbounded. This can be remedied by surfacing for a Global Positioning System (GPS) position update; however, for a deep-operating AUV, the transit to and from the surface will be both time-consuming and could introduce navigation errors. Docking is a capability central to incorporating AUVs into seafloor observatories. This is a particularly complex capability, as it requires several levels of interaction between a vehicle and a docking facility. These include the following: Homing: The vehicle must be capable of finding its way to a dock. Capture: The vehicle must be capable of latching to the dock. If it misses, it must be capable of detecting a missed approach to try again. Connection: A physical connection must be established between the dock and the AUV to provide power and communication links and to physically constrain the vehicle. Data download: Docking provides a mechanism for downloading data from the vehicle and into the data storage facilities on the dock so that at least some subset of those data can be transferred back to shore. Without such a capability, the value of the data stored on the vehicle will discourage further use of the AUV in case of loss of the vehicle. Battery recharge: Docking provides an opportunity to recharge the batteries of an AUV, which greatly increases the number of surveys an individual AUV can achieve.
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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE Mission upload: To realize the full flexibility of an AUV, the capability to upload new missions to the vehicle from the dock and, by extension, from shore should be established. Undocking: Initiating a new mission will involve the release of the vehicle from the docking station. Acoustic communications: For some applications and classes of observatories, it would be attractive to have a continuous communication link between the vehicle and the observatory. All the capabilities above have been demonstrated; however, it is likely to take several years of sustained effort to make these capabilities routine. Docking capabilities are currently receiving substantial attention and investment from groups outside the research community, such as the U.S. Navy. This external support should help expedite the development of this critical capability. Inclusion of one or more AUVs in an observatory can substantially impact the design of the observatory. Not only do AUVs have significant power needs, but the data produced by AUVs can impose substantial demands on observatories relying on satellite communications for data transfer. A rough order-of-magnitude appreciation for these issues can be gained by considering two AUVs types. A water-column AUV might be equipped with sensors consuming little power and producing a low volume of data. An imaging AUV might be equipped with a sonar system that would consume substantial power and produce gigabytes of data. A water-column AUV might log data at a rate of 10 Mbytes/hr; however, a scientist on shore might be satisfied with a very small subset of this data. For example, a time stamp, position, and three sensor readings every 10 seconds with single-floating-point precision would result in approximately 10 kBytes/hr. The effective average data rate is further throttled by intermittent AUV operations. If one runs the vehicle 1 hour out of 10, then the resulting data stream would be 1 kByte/hr on average. Power consumed by this AUV might conservatively be on the order of 200 W, which at 5 km/hr translates to 40 W/hr per kilometer of distance surveyed. Assuming an operational profile of 1 hour of operation out of 10, the average power required from the dock will be greater than 20 W by a factor relating to the efficiency of power transfer and battery recharging (probably no worse than a factor of 2). A sonar imaging platform might produce the same amount of data as discussed above, plus an additional GByte/hr for a system such as sidescan sonar. Clearly, this is a high-bandwidth system, even if one succeeds in substantial data compression. Furthermore, the power consumption of such a vehicle could be closer to 300 W, resulting in a correspondingly higher power demand on the dock. For a moored observatory, the data produced by such a
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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE vehicle would have to be stored at the docking station (storing it on the vehicle would create the risk of losing all data every time the AUV was operated), creating a substantial mass data-storage demand. The rapid advance of AUV capabilities is being led by a strong international community of AUV developers. For the most part, oceanographic and military uses of AUVs have been pioneered in the United States, funded primarily by the Office of Naval Research, the Naval Oceanographic Office, and the National Science Foundation. There are several academic research groups in the United States that are capable of fielding AUVs for oceanographic operations, but given the commercial availability and relative affordability of AUVs, the number of institutions with operational oceanographic AUV capabilities is likely to rise dramatically in the next few years. Recently, the offshore oil and gas industry has demonstrated a growing interest in AUVs for deep-water surveys driven by the combination of the move of offshore drilling to greater water depths and the increasing maturity of AUV capabilities. In the late 1990s, activity such as the Shell Oil development of the Mensa field in the Gulf of Mexico demonstrated that highly profitable oil and gas fields existed in depths in excess of 2,000 meters. These developments and the realization that the deepwater part of the ocean represents the largest unexploited region of the Earth, led to a number of oil companies demanding that their contractors be capable of supporting extraction operations to 3,000 meters. One critical requirement for this capability is the creation of high-resolution maps for planning and installing subsea production facilities. Such surveys are presently accomplished with towed platforms. However, AUVs offer the prospect of achieving both increased economic performance and higher data quality. Motivated by these factors, two marine survey companies have been contracted to construct AUVs for deepwater survey service. Depending on the success of these initial forays into the AUV arena, there is the potential for the multi-billion-dollar offshore oil industry to become significant AUV users. Historically, the offshore oil and gas industry has not directly invested in AUV development, but this is changing rapidly though the network of contractors who provide equipment and services and who are highly motivated to develop such capabilities. Marine survey companies are driven by the desire to gain a competitive edge in acquiring oil industry contracts, AUV manufacturing companies are motivated by the sales prospects, and sensor and subsystem supplier companies also want a share of the new market. While this has seeded a wide range of technology development, it is important to note that the economic drivers for offshore operations are very different from those of a seafloor observatory network as discussed here. Consequently, the primary effect of the advent of oil and gas industry activity in the AUV area will be the creation of a broader base of expertise and technology rather than providing direct solutions for oceanographic problems.
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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE FUTURE DEVELOPMENTS NEEDED AUVs today are typically serviced at frequent intervals. To realize their full potential, AUVs must be capable of remaining underwater and operating for extended periods without human servicing. Furthermore, docking remains an experimental capability that must be made reliable and efficient to enable extended, frequent operations of AUVs within a seafloor observatory. While existing navigation and power systems are sufficient to facilitate AUV use at seafloor observatories, improvement in these areas could greatly improve the utility of AUVs. REMOTELY OPERATED VEHICLE TECHNOLOGY FOR SEAFLOOR OBSERVATORIES ROVs are likely to play an important role in installing, servicing, and repairing seafloor observatories. Fortunately, ROV technology has been advancing rapidly, both within the oceanographic community and the commercial sector. A wide range of ROV capabilities are available, from systems optimized for high-fidelity control and mapping, to so-called work vehicles capable of delivering hundreds of horsepower of useful work at great depths. While observatory requirements for ROVs are difficult to predict, the current pervasive use of these systems lends a high degree of confidence that the oceanographic and commercial sectors should be capable of supporting seafloor observatory initiatives. The largest pool of deep-rated ROVs is in industry. Oceaneering alone has an inventory of 76 ROVs with depth ratings of 3,000 m. However, the oceanographic community is routinely using a growing number of deep-rated ROVs, and these systems are increasingly in high demand. Table 4-3 lists systems rated deeper than 1,500 m. Some common uses for ROV technology include the following: High-resolution site mapping—High-resolution seafloor maps are important for site preparation prior to the installation of a seafloor observatory. Higher-resolution seafloor maps are obtained by placing mapping sonar systems on platforms flying relatively close to the seafloor. While towed vehicles are routinely used for producing these surveys, the highest quality maps are produced from vehicles capable of flying precision tracks, such as ROVs and AUVs. Installation of instrumentation—Many types of scientific instrumentation will require installation on or near seafloor observatories. Only a fraction of this instrumentation will exist on or near the central node. Many other instruments will be placed at considerable distances from the node. Because of this, it will be important for an ROV to be capable of spooling out several kilometers of
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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE TABLE 4-3 Deep-rated Remotely Operated Vehicles Vehicle Depth Rating Operating Institution Builder Support Vessel Dolphin 3K 3,000 m JAMSTEC JAMSTEC Natsushima Hyperdolphina 3,000 m JAMSTEC ISE Kaiyo Jason 6,000 m WHOI WHOI Atlantis II/Ship of opportunity Jason IIb 6,500 m WHOI WHOI Atlantis II/Ship of opportunity Kaiko 10,700 m JAMSTEC JAMSTEC Kairae ROPOS 5,000 m Canadian Scientific Submersible Facility ISE Ship of opportunity Ventana 1,830 m MBARI ISE Pt. Lobos Tiburon 4,000 m MBARI MBARI Western Flyer Victor 4,000 m IFREMER IFREMER Ship of opportunity aDelivered but not yet operational. Additional vehicle purchased as a spare. bUnder development. Projected to be available fiber-optic cable with low-power conductors to trickle-charge batteries. Scientific packages could be configured as drop-able tool sleds or could be free-dropped from the surface, maneuvered into place by an ROV, and connected to the central node. As proven by the Japanese, it is currently feasible to move large instruments to specific sites after surface deployment using ROV-controlled buoyancy packages. On occasion, seismometers and similar instrumentation may need to be buried or coupled to the seafloor. ROVs with a jetting capability can easily accomplish these tasks. Servicing installed instrumentation—Even instrumentation positioned deep in the water column can experience biofouling, sediment accumulation, or short-term failures. Standard methods of mounting instrumentation and connector protocols can make instrument replacement routine using a variety of ROVs. There is currently an American Petroleum Institute standard for ROV intervention that should be reviewed for applicability to seafloor observatories. Data downloads are also an important component of ROV servicing that are already being accomplished using inductive modems. Furthermore, short-distance laser data downloads could be used where applicable. It is standard practice in the oilfield to use a hydraulic lance to actuate, latch, and release functions for instrumentation. Seawater hydraulics would provide an environmentally acceptable solution to latching or releasing packages.
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Illuminating the Hidden Planet: THE FUTURE OF SEAFLOOR OBSERVATORY SCIENCE Servicing node components—Large nodes should be designed to allow for modular replacement of major components by an ROV. This could be accomplished by unlatching components using seawater hydraulic lances and underwater mateable connector interfaces. This capability will lead to extended lives for seafloor observatory components. Burying cable—In certain areas, such as continental shelves, cables will need to be buried to reduce damage by anchors, fishing trawlers, etc. ROVs are becoming mature enough that, with proper design of observatory hardware, there should be little risk in using ROVs to service observatory systems. The oceanographic community has already demonstrated the use of ROVs in various aspects of observatory work, such as the Woods Hole Oceanographic Institution (WHOI) installation and servicing of Hawaii-2 Observatory (H2O) and Monterey Bay Aquarium Research Institute (MBARI) work in Monterey Bay with the Ventana and Tiburon ROVs. Furthermore, the offshore oil industry is increasingly placing complex systems on the seafloor in deep water that demand ROV serviceability. The commercial undersea cable industry has a set of ROV tools, including plows and tractors, to provide cable burial, maintenance, and repair capabilities. Consequently, there is a growing industrial base on which to build observatory ROV capabilities.
Representative terms from entire chapter: