National Academies Press: OpenBook

Practical Applications of a Space Station (1984)

Chapter: OCEAN OPERATIONS

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Suggested Citation:"OCEAN OPERATIONS." National Research Council. 1984. Practical Applications of a Space Station. Washington, DC: The National Academies Press. doi: 10.17226/18603.
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Suggested Citation:"OCEAN OPERATIONS." National Research Council. 1984. Practical Applications of a Space Station. Washington, DC: The National Academies Press. doi: 10.17226/18603.
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Suggested Citation:"OCEAN OPERATIONS." National Research Council. 1984. Practical Applications of a Space Station. Washington, DC: The National Academies Press. doi: 10.17226/18603.
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Suggested Citation:"OCEAN OPERATIONS." National Research Council. 1984. Practical Applications of a Space Station. Washington, DC: The National Academies Press. doi: 10.17226/18603.
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Suggested Citation:"OCEAN OPERATIONS." National Research Council. 1984. Practical Applications of a Space Station. Washington, DC: The National Academies Press. doi: 10.17226/18603.
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Suggested Citation:"OCEAN OPERATIONS." National Research Council. 1984. Practical Applications of a Space Station. Washington, DC: The National Academies Press. doi: 10.17226/18603.
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Suggested Citation:"OCEAN OPERATIONS." National Research Council. 1984. Practical Applications of a Space Station. Washington, DC: The National Academies Press. doi: 10.17226/18603.
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Suggested Citation:"OCEAN OPERATIONS." National Research Council. 1984. Practical Applications of a Space Station. Washington, DC: The National Academies Press. doi: 10.17226/18603.
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Suggested Citation:"OCEAN OPERATIONS." National Research Council. 1984. Practical Applications of a Space Station. Washington, DC: The National Academies Press. doi: 10.17226/18603.
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Suggested Citation:"OCEAN OPERATIONS." National Research Council. 1984. Practical Applications of a Space Station. Washington, DC: The National Academies Press. doi: 10.17226/18603.
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Suggested Citation:"OCEAN OPERATIONS." National Research Council. 1984. Practical Applications of a Space Station. Washington, DC: The National Academies Press. doi: 10.17226/18603.
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Suggested Citation:"OCEAN OPERATIONS." National Research Council. 1984. Practical Applications of a Space Station. Washington, DC: The National Academies Press. doi: 10.17226/18603.
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Suggested Citation:"OCEAN OPERATIONS." National Research Council. 1984. Practical Applications of a Space Station. Washington, DC: The National Academies Press. doi: 10.17226/18603.
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Suggested Citation:"OCEAN OPERATIONS." National Research Council. 1984. Practical Applications of a Space Station. Washington, DC: The National Academies Press. doi: 10.17226/18603.
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Suggested Citation:"OCEAN OPERATIONS." National Research Council. 1984. Practical Applications of a Space Station. Washington, DC: The National Academies Press. doi: 10.17226/18603.
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Suggested Citation:"OCEAN OPERATIONS." National Research Council. 1984. Practical Applications of a Space Station. Washington, DC: The National Academies Press. doi: 10.17226/18603.
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Suggested Citation:"OCEAN OPERATIONS." National Research Council. 1984. Practical Applications of a Space Station. Washington, DC: The National Academies Press. doi: 10.17226/18603.
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OCEAN OPERATIONS* INTRODUCTION As a result of recent economic, political and scientific developments, the world has entered a period of increasing interest in ocean operations. Some of the factors accounting for this new interest are the establishment of national economic zones extending 200 nautical miles from the shorelines of coastal nations, growth in size and number of oceangoing ships, movement of petroleum exploration into the offshore regions of as many as 50 nations (in addition to the 50 countries that had offshore oil wells in l979), increasing importance of worldwide fishing, prospects for ocean-bed mining, concern about protecting the ocean from dumping of toxic wastes, the promise of power generation from ocean waves and thermal differentials, and the expansion of naval defense activities. These developments result in growing needs, among government and private concerns having oceanic responsibilities or interests, for ocean data. This chapter addresses space systems as they might be used for obtaining oceanic data to meet the needs of the user community. This chapter deals principally with the use of remote sensing from space in ocean operations. We recognize that navigation satellites are becoming important in ocean operations, and this subject is treated briefly in the next chapter (Satellite Communications). *The Panel acknowledges the valuable contributions made by John W. Sherman III of the National Oceanic and Atmospheric Administration. 4l

42 From a physical standpoint, the world's oceans cover more than two-thirds of the surface of the earth, occupying more than 350 million square kilometers, and having a volume of nearly l.5 billion cubic kilometers. Approximately 5 to 8 percent of the oceans are covered by ice. The oceans support a multitude of physical, biological, and chemical processes, and constitute vital national and international resources. In considering the utility of satellite remote sensing to the oceanic community, two factors need to be taken into account: from the scientific viewpoint, major ocean basins behave as entities; from the political viewpoint, the developing body of international sea law will eventually have an important impact on various ocean activities. The concept of the oceans as entities drives many of the requirements for synoptic coverage by satellites. For the purposes of oceanography, the earth may be considered to be divided into halves—north and south—at the meteorological equator, which generally lies north of the geodetic equator. The oceans behave as entities because the gross water circulation of each of the major ocean basins of the world—i.e., the North Atlantic, South Atlantic, North Pacific, South Pacific, and Indian oceans—is largely self-contained; the circulation in each basin is rotary in the upper layers, with little exchange of water between the two hemispheres. Some of the the polar regions are ice-covered much of the year and behave to a large extent as separate oceanic areas. They do, however, interact with lower-latitude seas, and it is the marginal areas of the polar regions that are the most environmentally active. The surface circulation of the ocean basins is a major mechanism for global dispersal of incoming solar heat, initially collected in low latitudes. Because of the nature of the flow within basins, problems of water circulation must be considered on an oceanic scale, taking in the far northern and southern extremes of the major basins. Thus, two distinct areas are of concern to oceanographers: the major ocean basins over their full latitudinal extent, and the polar areas. In dealing with oceanic-scale problems, then, minor increases in latitudinal coverage are of small value until the final increment—which includes the basin margin—is reached. The development of a new body of international sea law may have strong implications in many fields of oceanic endeavor. National sovereignty over activities in and on

43 the sea now extends 200 nautical miles offshore. Some measure of international control on the remainder of the oceans can also be anticipated—the recent Law of the Sea Treaty, for example, provides for control over ocean-bed resources. The establishment of the 200-mile national boundary greatly inhibits access of fishermen and scientists to the coastal waters of other nations. The effect is to drive both groups farther out onto the high seas—outside the current jurisdiction of coastal nations. As restrictions are placed on fishing and research ship activity, it must be expected that needs for satellite-based navigation and communications services will increase, and remotely sensed data in the coastal regions will become more important. The Panel concludes that to be of significant value, observations from space must cover the major oceans and require spacecraft in polar or nearly polar orbit. Conversely, observations from spacecraft on orbits having inclinations in the range of 25° to 35° can contribute relatively little additional insight into problems related to oceans as entities, nor can they meet the increased need for navigation and communication services. CURRENT STATUS OF REMOTE SENSING OF THE OCEANS The areas in which ocean data are useful are diverse, and reponsibilities for the oceans and activities in or upon them is dispersed among many agencies, organizations, and individuals. In the federal government alone, such agencies as the departments of State, Defense, Transportation (Coast Guard), and Energy, the Environmental Protection Agency (EPA), the National Aeronautics and Space Administration (NASA), the National Oceanic and Atmospheric Administration (NOAA), and the National Science Foundation (NSF) need or acquire ocean data. Many state and local government agencies can be added to the list. In the private sector, organizations using ocean data include such enterprises as shipping concerns, fisheries, oil and gas producers, and several international consortia formed for ocean mining. Individuals who use ocean data include commercial fishermen and marine scientists.

44 Ocean Observations from Aircraft Ocean data obtained by observations from aircraft provide an overview of ocean surface conditions that is of importance in research. Aircraft using air-dropped buoys can obtain data in remote areas and over wide expanses of ocean on a near real-time basis. Below are some examples of research and operational uses by the U.S. Coast Guard, NASA, NOAA, and the Navy of ocean observations obtained from aircraft. The Coast Guard uses information obtained from aircraft in its search and rescue operations as well as in its efforts to patrol the 200-mile economic zone. In addition, the Coast Guard uses such data in oceanographic surveys, ice patrols, and oil-spill responses. Also, airplanes equipped with radar, infrared sensors, and optical cameras are used for oil-spill surveillance. NASA has used aircraft such as the high altitude TR-l, the C-l30, and the C-54 in experiments to remotely sense the oceans for sediment transport, marine pollution, phytoplankton dynamics, sea ice, and ocean dumping and other activities. NCAA's National Marine Fisheries Service (NMFS) charters airplanes from private companies to observe the 200-mile economic zone, primarily to support the Coast Guard in the control of foreign and domestic fishing activities. NMFS has used aircraft-mounted television cameras to search for schools of menhaden, an economically important fish abundant along the U.S. Atlantic coast. Also, NOAA conducts a variety of ocean observations as part of its environmental research program, and the National Weather Service uses "hurricane hunter" aircraft to obtain data for hurricane reconnaissance. The Navy uses aircraft to conduct acoustic, sea ice, and magnetic experiments in a wide range of programs. Ocean Observations from Satellites Oceanic measurements from satellites began in the l960s with spacecraft such as NASA's Nimbus series of experimental satellites, NOAA's TIROS and improved TIROS series of global weather satellites, and the Defense Meteorological Satellite series (DMSP). Although some oceanographic data were produced by these spacecraft,

45 providing data to the ocean community was not their primary mission, and the data were more a matter of curiosity than of use to those who had access. Experiments specifically for oceanography began with a microwave experiment package aboard Skylab* in l973. The package included an altimeter, a scatterometer, and a radiometer. Another ocean altimetry experiment followed on GEOS-3 (Geodetic and Oceanographic Satellite) in l975. In l978, Seasat—a "proof of concept" satellite dedicated to oceanography—carried an array of sensors. The mission was cut short by a power failure after three and one half months. Seasat provided excellent data for the research community, and its measurements met their technical objectives. Seasat's brief lifetime, however, did not permit accomplishing planned experiments in operational use of the data, such as optimum ship routing forecasts. With the demise of Seasat, oceanographers turned to other satellites for whatever data could be obtained. Although oceanographic data have been obtained from a variety of sensors on other satellites (Nimbus 7, GEOS, etc.), the data as a whole do not meet the requirements for research or operations. Ocean operations and research need 24-hour global coverage, sea surface observations by several instruments, and the ability to obtain repeat coverage, at least once a day. The Panel is in agreement with the observations of the Space Science Board's Committee on Earth Sciences that "in the area of ocean dynamics, space techniques offer the only practical means to determine the surface boundary conditions for general circulation of the ocean" (Committee on Earth Sciences, l982). A National Oceanic Satellite System (NOSS), a proposed cooperative program among NOAA, the Department of Defense, and NASA, would have filled many requirements for oceanic operations. As originally conceived, NOSS was a two-satellite program using proven sensors for operational data and research. The system was designed to operate for five years (until about l99l), and it was hoped that a fully operational system would follow. NOSS was cancelled in l98l. NASA's plans still include an ocean satellite, the Dynamic Topographic Experiment (TOPEX). Its mission is to * Skylab was a NASA spacecraft that supported three-man crews in orbit for up to three months.

46 obtain ocean topography accurate to 2 cm, averaged over 4 km on the ocean surface. In addition, as a low-cost alternative to NOSS, NASA is examining the possibility of flying, as piggyback payloads on various spacecraft, individual instruments such as a scatterometer and an ocean color sensor. Also, NASA has agreed to perform with Canada's Division of Energy, Mines and Resources a bilateral study of the requirements for a future satellite having a synthetic-aperture radar as its principal instrument—the RADARSAT-FIREX mission study. The Navy, with the Defense Mapping Agency, is developing a small satellite to acquire geodetic data, filling a void left by the failure of Seasat. The Navy updated its operational needs for ocean data, and has proposed a navy remote ocean sensing satellite system (NROSS). Finally, other nations of the world are developing ocean-data satellites. Japan's National Space Development Agency has scheduled launch of a maritime observation satellite in l986, and the European Space Agency has completed preliminary design studies of a remote sensing satellite system, tentatively scheduled for launch in l987. THE NEED FOR OCEAN DATA—MAJOR USES This section is a discussion of functional areas for which ocean data are needed, indicating where the data could be provided by remote sensing from satellites. The areas discussed are protection and control of economic zones; coastal preservation; fisheries development; offshore oil and gas exploration, drilling, and production; mineral extraction; power generation; ocean pollution; sea ice monitoring; ocean research; and naval activities. Protection and Control of Economic Zones Today, among many nations there is acceptance of a functional economic zone extending 200 nautical miles offshore. One section of the Law of the Sea Treaty, mentioned earlier, will give coastal nations control of their adjacent waters to 200 miles offshore. This authority implies responsibilities, such as protecting resources, monitoring traffic, and providing maritime assistance. Also, it may imply the eventual authority to control tens of thousands of oceangoing ships, just as

47 air traffic has been controlled, worldwide, for decades. Policing the 200-mile economic zone in the United States has challenged the Coast Guard, which faces constantly rising costs of ship operations and the diminishing size of its operational fleet. Routine surveillence of large ocean areas by remote sensing would make it possible to use Coast Guard vessels for direct action when specifically needed, and thus to operate more efficiently. The ability of satellite sensors to detect, track, and monitor activities of oceangoing ships is well demonstrated. Therefore, the Panel recommends development of this capability for effective surveillance, control, and management of maritime activities in the offshore economic zone of the United States. Coastal Preservation Coastal zones are subject to atmospheric, oceanic, and alluvial influences. These influences affect habitability, suitability for construction, and industrial and military operations on and near shore. Remote sensing can complement in-situ measurements of factors that affect the coastal zones and can detect alluvial sand deposition, flooding, and beach erosion. In addition, wave height and shallow bathymetric measurements would further increase the use of remotely sensed data by those concerned with the protection of the coastal zone. Fisheries Development In commercial ocean fisheries, remotely sensed data is of principal use in operations concerned with stock harvesting and stock management. For stock harvesting, fishermen need an all-weather observing system (for navigation, hazardous warnings, etc.); sea surface temperature estimates (for locating preferred fish habitats); and ocean color monitoring (for determining the presence of plankton). For stock management, scientists need ocean color monitoring (for detection of chlorophyll concentrations); surface wind measurements (for estimation of surface-water transport); and a detection and tracking capability (for determining the size of schools of pelagic fish and for tracking sea mammals). Remotely sensed data are being used today by commercial fisherman and fishery scientists. However, major

48 improvements are needed to meet the needs of this community. Most important are a system for hazardous warning; sea surface temperature estimates; an ocean color monitoring capability; a detection and tracking capability; and better estimates of wave height, rainfall, and wind speed and direction. For fishing activities, the most important areas are in the 200-mile economic zone. However, some fishing occurs on the high seas, which requires coverage over a wide range of latitudes, from the equator to polar waters. Thus, a near-polar orbit would be necessary to benefit fishing activities. Offshore Oil and Gas Exploration, Drilling, and Production Today there are approximately 25,000 petroleum wells in offshore areas of the United States producing about l2 percent of U.S. oil and 27 percent of U.S. gas. In addition, offshore oil wells in 50 countries provide 20 percent of the world's oil production. Fifty more countries have offered offshore sites for petroleum exploration. Many experts in the oil industry, government, and academia believe that in the decades ahead the remaining onshore resources will decline in importance while yet-unexplored offshore areas, involving more hostile environments, more remote locations, and deeper water, will increase in importance. Offshore petroleum activities involve three distinct phases: exploration, drilling, and production. Each phase has unique needs for data and information. Exploration is usually done by specialized research ships. While they are somewhat more weather sensitive than are cargo vessels, their needs for forecasts are similar to those of other surface ships and they can usually avoid adverse weather. Offshore drilling operations are carried out from bottom-mounted platforms or from mobile ships or submersible platforms. While drilling is in progress, an active connection extends from the mobile or fixed unit into the seabed, so that evasion of bad weather is difficult for mobile platforms and impossible for fixed platforms. Accurate advance information on weather and waves—especially on potentially severe conditions—is required. In the production phase, when hydrocarbons flow via seabed pipelines to the shore, sensitivity to environmental conditions is somewhat less, but reliable

49 forecasts are still needed. Improvements in weather and ocean observations by remote sensing from space, accompanied by improvements in weather models, could produce a forecasting system that would meet the needs of oil and gas companies. Mineral Extraction Although some mines near coastlines have shafts extending into underwater areas, the term "ocean mining" refers to the collection and processing of nodules that are found on the ocean floor. Rich in various metals such as manganese, copper, and nickel, these nodules hold the promise of a substantial mineral harvest. The technologies needed to gather and process the nodules are in hand: several international consortia have been formed for extensive ocean-mining operations. U.S. companies planning deep-ocean mining face considerable uncertainty because of legal, economic, and political circumstances. Nevertheless, data on ocean weather, waves, and currents will be of great importance to any ocean-mining operation. Power Generation Certain natural phenomena in the oceans—temperature gradients, wave action, and salinity gradients—hold promise for generation of electrical energy. Ocean thermal energy conversion and power generation from wave action have been demonstrated and await favorable economic conditions in order to proceed. With the costs of electrical energy continually escalating, the Panel believes that these techniques will be required during the period considered in this study (to the year 2000). To support offshore power generation, as well as power stations built near coastlines, ocean data are needed for site selection, assessment of pollutant transport, environmental protection, design of thermal and wave action systems, and monitoring of physical, chemical, and biological conditions. Satellite observations seem to be the logical choice for meeting this demand.

50 Ocean Pollution In recent years, the ocean has become a dumping ground for outmoded ships, radioactive materials, chemicals, and other pollutants. Pollution from shipping and offshore oil wells, and effluents from onshore power stations and whole cities, are endangering the ocean environment— especially in coastal areas. With commercial activities continuing to increase, the threat to the quality of the ocean environment will rise. Monitoring ocean pollution requires observations of ship traffic and observation of the effects of pollution on the water. The first function could become a special task within a general program of monitoring ocean traffic by satellite observations—a service that may well develop for other reasons, such as control of fisheries and direction of ship traffic. The second function is more complex in that some factors, such as oil spills or particulate matter, can be observed with current techniques while other, more subtle changes, such as the effluent from a chemical plant, are beyond the present capabilities of remote sensing. The need for development of these techniques is suggested in the section "Future Needs." However, only satellites can fill the need for monitoring the oceans on a synoptic scale. Sea Ice Monitoring The earth is a heat engine; energy from the sun is received in the tropics and lost from the polar regions. Sea ice in the Arctic and Antarctic is a result of that heat loss. Where sea ice meets warm water, it melts at an unsteady boundary. The extent of ice varies with the seasons, with a six-month phase difference between north and south latitudes. For reasons that are not yet understood, ice extent varies from one year to the next. The shipping industry, fishermen, and others operating in polar regions refer to "good ice" years and "bad ice" years. Bad ice is a lot of ice getting in one's way, and good ice is the lack of the same. Clouds and fog are frequent where ice drifts; hence, detection and tracking of this potential hazard should be done by microwave sensors, such as Seasat's synthetic-aperture radar. The global demand for fossil fuel has led to increased activity in the Arctic, accompanied by a need for more and better information on the extent and motion of sea

51 ice—particularly where the ice is thicker. Thick ice presents a hazard to shipping, to offshore installations, and to structures onshore as well. Thin ice, while not as hazardous, can be a problem for fishermen. Because thin ice comprises most of the vast area of annual fluctuation, it is of interest to scientists. In drifting ice, leads (channels of water through ice fields) can open and close in hours or even minutes, so that forecasters, ship operators, and others need frequent coverage. Sea ice monitoring is another area where satellites can play an increased role. The use of sensors operating at several frequencies would help remedy the problem of determining sea ice thickness by remote sensing. Ocean Research and Science Of the four major disciplines in ocean research—physical oceanography, biology, chemistry, and geology—physical oceanography has benefited most from remote sensing, because the ocean is most active in its upper layers, where phenomena of interest can be observed. Biologists have also benefited, since oceanic life is concentrated near the surface. However, chemists and geologists have been able to make little use of remotely sensed data, because few chemical factors and almost no geological phenomena are observable by remote sensing. The Panel believes that this situation is not likely to change. For ocean research, remote sensing holds some important advantages over conventional shipboard sampling. Research vessels are limited to advancing a hundred or so miles per day, and are further limited to local observations. On the other hand, satellites can scan a very large area at a rate that is fast compared with the rate of most oceanic processes. Thus, remote sensing can provide amounts of data many orders of magnitude larger than those from a fleet of research ships. Nevertheless, in those disciplines that can benefit from the use of remote sensing data, far less than full use has been achieved because of the problems of handling large masses of data and a lack of confidence in the validity of the data (due in part to inadequate ground-truth validation). Broad professional acceptance may well have to await the arrival of a new generation of oceanographers, who will have grown up with remotely sensed data, just as they have grown up with computers.

52 In addition, many persons in government agencies that provide financial support for oceanic research share the skepticism of some scientists about remotely sensed data. For years, they have supported research done from a ship by a professor, some students, and a few technicians. One short cruise every year or so has provided data adequate for several years of study. To process and analyze the flood of information from a satellite requires different talents and more people. Sponsors of scientific research are often not geared conceptually or financially to deal with this problem. The result is a self-perpetuating conservatism, and as a consequence valuable data are being neglected. The Panel believes that sponsoring agencies should be alert to novel approaches in ocean research and should be prepared to support them. On the other hand, the remote sensing community must become more sensitive to the data and information needs of ocean scientists and ocean operators. Naval Activities Most naval operations, as well as the logistics system that support them, can benefit from timely receipt of suitable ocean data. The Navy has established an operational requirement for satellite measurement of oceanographic data (SHOP OR-W0527-OS), which specifies the horizontal resolution, precision, and accuracy of oceanic measurement needed for naval operations. In addition, the Navy is developing a system for delivery of this data to fleet units and command centers. The system will use data from several satellites, merge the data in processing operations, and disseminate the data in processed form. REQUIREMENTS FOR SPACECRAFT FOR OCEANIC REMOTE SENSING This section identifies technological requirements for a space station or space platform with oceanic remote sensing capability. Preceding that discussion is the Panel's evaluation of the Space Shuttle as a system for delivering ocean survey satellites to orbit and as a test bed for sensors designed for ocean observations.

53 The Space Shuttle as Delivery System and Test Bed As a delivery system, the Space Shuttle is quite compatible with requirements for ocean-data-gathering space systems, which might involve delivering a free-flying ocean satellite into orbit, carrying pallet-mounted instruments, or transporting modules to be incorporated into a space station or space platform. In studies of the National Oceanic Satellite System by NASA, the Department of Defense, NOAA, and three systems contractors, the ability to package the key ocean-data sensors on a free-flying satellite, which could be delivered to orbit by the Shuttle and retrieved by the Shuttle for refurbishment or repair, was well established. In addition to its capabilities as a delivery system, the Space Shuttle has proven itself to be an effective test bed. While still in its R&D phase, the Shuttle carried payloads of experiments as secondary missions. A pallet aboard the second Shuttle carried experiments for NASA's applications program. Though the instruments were operated only for a limited time, the results were useful. The Panel concludes that the Shuttle will be useful both as a delivery system for satellites with oceanic remote sensing capability and as an orbiting test bed, carrying experimental ocean-data-gathering instruments. Free-Flying Observatories with Space Station Support Orbit requirements and other limitations may make it impractical to use a space station or space platform to carry ocean-monitoring instruments. In such cases the instruments might be placed on free-flying spacecraft, which could be located within range of astronauts from a space station, or could receive communications, power, or other support from the space station. Personnel on board a station might be able to repair the free-flyer or to replace parts. If power could be transmitted from a central power source, power-generating equipment on board the free-flying spacecraft could be minimized. Operational control of free-flyers from a station and use of a station to relay data to the ground could simplify the design of ocean-monitoring satellites. The Panel concludes that free-flying observatories would benefit from services that might be provided by a

54 space station, and recommends that these possibilities be examined during future planning for a space station. Some Key Factors The Panel was able to establish some requirements for a space station or platform in order for it to be useful for acquiring ocean data. Three key factors—instruments, data handling, and orbit selection—will determine whether a space station or platform can efficiently provide ocean remote sensing data. A discussion of these factors follows. Instruments The types and numbers of sensors that have been used or are planned for measuring ocean data are as follows: Visible light sensors—five in use and four planned Infrared radiometers—eleven in use and two planned Passive microwave sensors—four in use and two planned Active microwave sensors and lasers—four in use and three planned The Panel concludes that sensor technology has progressed to the point where the most important ocean measurements can be obtained with available sensors. To obtain the important ocean data, a variety of sensors should be used. For example, instruments operating in the visible or infrared bands provide measurements with high spatial resolution but cannot "see" through clouds, whereas microwave instruments can see through clouds or darkness but have poor spatial resolution. Also, since the antennas for microwave instruments must be large to provide adequate spatial resolution, interference with instruments while in orbit may be a problem. In the future, it may become desirable to use new sensors—for example, sensors that can measure ocean depths, carbon dioxide, surface chemical factors, or salinity. Some sensors, such as synthetic-aperture radars (SAR), provide data from which a variety of phenomena can be derived. A SAR was flown on Seasat with good results and on the OSTA-l pallet payload on the second Space

55 Shuttle. Microwave sensors can provide wind, wave, ice, and sea surface temperature data, which are needed by many users. Ocean color data, needed by fisheries and pollution specialists, can be obtained with instruments like the Coastal Zone Color Scanner carried on Nimbus 7. Data Handling If a full complement of ocean sensors is operated on a full-time duty cycle, one can foresee a requirement to transmit up to one gigabit (one billion bits) per second. This would appear to be a maximum requirement for ocean operations. On-board data processing or reducing the duty cycles of the instruments could relieve the demand on the data communication system. If humans are to aid effectively in observing the oceans from space, they will need tools to process and reduce data collected by onboard sensors. An image processing and display capability on board the space station would permit interactive information manipulation and analysis, and thus make it possible to reduce data transmission requirements. Without such capability, the human role would be limited to instrument tending. Many users are not equipped to handle large quantities of data or data that must be processed to yield useful information. Many research ships are not equipped for large-volume data exchange, nor do they have computer facilities and peripherals necessary to assimilate it. Industrial users such as fishermen are even less adequately equipped. Instead of data, they need useful information, such as the coordinates for points where fish are to be found. Most users, in fact, would prefer that the conversion of data to useful information be done by someone else—at no cost to the user. Obviously, the interface between the generators of large quantities of raw data and the potential customers has not been adequately addressed. In some respects, lukewarm consumer support has been due to a lack of appropriate packaging and marketing. The Panel believes that for remote sensing from space to achieve its potential utility, data products will have to be made readily usable for prospective users. Orbit Selection Ocean users need global coverage, with observations day and night under all weather conditions. A high-inclination,

56 sun-synchronous orbit—i.e., an orbit with an inclination of approximately 98°, at an altitude of about 400 nautical miles—will satisfy most users. For some special uses, other orbits may be needed, but even these cases will require relatively high-inclination orbits—for example, at least 62° for TOPEX and l08° for the Navy's geodetic satellite. The Panel concludes that high-inclination orbits are needed to observe whole ocean basins; low-inclination orbits—25° to 35°, for example—will be only marginally useful. FUTURE NEEDS Advances in Direct Measurements and in Monitoring Scope Advances in the technology of oceanic remote sensing from space can be envisioned in two categories. One category is the kinds of ocean data that can be measured or characterized by remote sensing. The other is the scope of ocean monitoring in terms of coverage and completeness, duration, and dissemination of information products. Advances in either of these categories would greatly increase the usefulness of remotely sensed data to the ocean community. With regard to kinds of data, the present and foreseeable capability consists of direct measurement of physical quantities (e.g., surface water temperature, visual color, roughness patterns, wave height, and topography) at or near the air-sea interface. From these measurements, surface wind speed and direction, currents, and chlorophyll concentrations can be inferred. The utility of oceanic remote sensing would be extended by the capability to make measurements of interest to marine biology, chemistry, and geology. The direct measurement of carbon dioxide concentration is an example of this extension. Similarly, one can envision benefits to ocean resource management should it become possible to measure primary chemical nutrients and larger marine organisms. Detection of concentrations of fish, combined with dissemination of the information to fishermen on a useful time scale, would have an enormous impact on an industry that spends the major portion of ship time hunting rather than harvesting. New active techniques (blue-green lasers, for example) may be capable of extending the depth

57 of remote sensing to tens of meters. Increases in sensing depth will benefit marine geology. The utility of remote sensing to coastal zone and estuarine studies could expand dramatically with even modest increases in sensing depth. The second category of important advance in capability identified by the Panel is that of the scope or scale of ocean monitoring. The elements that would be required for a comprehensive ocean monitoring system have been developed and tested. The important difference would be in scope of the total system rather than in the kind of measurements. Orbiting platforms could bring major improvements in system resolution and sensitivity. Use of larger apertures, of the order of tens of meters, would bring improvements in resolution. A large man-tended station would be consistent with the broad payload complement, the large apertures for the microwave instruments, and the requirement for long-term data continuity. Data Distrubtion and Utilization Because of the short temporal scales of some ocean phenomena, a major consideration is the timely availability of data end-products. Following is a discussion of some of the factors that are applicable either to an ocean satellite system or to a space station or platform carrying a complement of ocean sensors. Raw data must be available in near real-time to those responsible for sensor health, to value-added industries that convert data to information products, and to researchers involved in real-time experiments. This requires high-speed communication between remote sensing satellites, a space station, or a space platform and research and commercial users. Processed data should be made readily available to commercial and government centers charged with satisfying end-user needs for geophysical units and for analysis and forecast products. Ship-routing services, fishery location aids, and drilling platform advisories are activities in which information is needed at least twice daily. On the other hand, computer and other ocean-process modeling activities require a continuous flow of data for several years. Finally, it is necessary to establish, in concert with users, what subsets of raw and reduced data will be permanently stored.

58 CONCLUSIONS There is a growing need for ocean data. The requirements applying to ocean satellites would apply equally to space stations or space platforms carrying ocean-observing instruments. The acquisition of ocean data from space should be improved, collection of the data should be increased, and the data should be made available to ocean users in a timely manner and in formats that are useful to them. Since the oceans cover regions that extend nearly to the earth's poles, remote sensors must be carried on spacecraft in high-inclination orbits. Data from remote sensing instruments must be continuously validated by measurements made at the earth's surface from ships, buoys, and aircraft. The data from ships, aircraft, and buoys should be integrated with remotely sensed data from space in a single ocean-data system. With regard to the utility of man in space with respect to acquiring ocean data, the Panel makes the following observations. Human participation may be useful in the development of new instruments and for short-duration specialized experiments, but man would not play a meaningful role in the acquisition of data on a continuing basis. The Panel sees a need for the ability to assemble, repair, or modify remote sensing spacecraft in orbit. Seasat is a good example—it is understood that this costly spacecraft could have been restored to useful operation if the ability to retrieve it had existed. Another example is the construction of very large antennas. The Panel recommends that spacecraft be designed so that they can be repaired or modified in orbit. REFERENCES Committee on Earth Sciences. l982. A Strategy for Earth Science from Space in the l980's. Part l: Solid Earth and Oceans. Washington, D.C.: National Academy Press.

59 International Council of Scientific Unions. l980. Oceanography from Space. Committee on Space Research and Scientific Committee on Oceanic Research; Inter-union Commission on Radiometeorology. Venice, Italy. Joint Scientific Committee/Committee on Climate Change and the Ocean. l98l. Report of the Meeting on Coordination of Plans for Future Satellite Observing Systems and Ocean Experiments. Chilton, United Kingdom. National Advisory Committee on Oceans and Atmosphere. l98l. Ocean Services for the Nation: National Ocean Goals and Objectives for the l980's. Washington, D.C.: U.S. Government Printing Office. National Aeronautics and Space Administration. l98l. Satellite Altimetric Measurements of the Ocean. TOPEX Science Working Group. Pasadena, Calif.: Jet Propulsion Laboratory. National Aeronautics and Space Administration. l982a. Scientific Opportunities Using Satellite Surface Wind Stress Measurements over the Ocean. Satellite Surface Stress Working Group. Washington, D.C. National Aeronautics and Space Administration. l982b. Science Requirements for Free-Flying Imaging Radar (FIREX) Experiment. Pasadena, Calif.: Jet Propulsion Laboratory. National Aeronautics and Space Administration. l982c. Seasat Data Utilization Project Report. Pasadena, Calif.: Jet Propulsion Laboratory. National Center for Atmospheric Research. l98l. Needs, Opportunities, and Strategies for a Long-Term Oceanic Sciences Satellite Program. NASA/NOSS Science Working Group. Boulder, Colo. Ocean Sciences Board. l982. Two Special Issues in Satellite Oceanography: Ocean Dynamics and Biological Oceanography. Washington, D.C.: National Academy Press. Stewart, R. H. l982. Oceanography from Space. 33rd Congress of the International Astronautical Federation. Paris.

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The demonstrated capabilities of the Space Shuttle and rapid advancements in both ground- and space-based technology offer new opportunities for developing space systems for practical use, including a manned space station and one or more unmanned space platforms. The Space Applications Board conducted a study to determine the technical requirements that should be considered in the conceptual design of a space station and/or space platforms so that, if developed, these spacecraft would have utility for practical applications.

Practical Applications of a Space Station is a formal report of the study, in which six panels met, one in each of the following areas: earth's resources, earth's environment, ocean operations, satellite communications, materials science and engineering, and system design factors. Each panel was asked to consider what practical applications of space systems may be expected in their particular areas beginning around 1990. The panels were also asked to identify technological progress that would need to be made and that should be emphasized in order for space systems with practical uses to have greater utility by the time a space station might be available.

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