Platforms for Observation and Collection
Attainment of the challenging goals of the programs described in this report depends on the collection and analysis of materials and data. A wide variety of techniques, equipment, and research vessels are required for this task. The availability of satellites and in situ moorings will not diminish the importance of surface vessels in oceanographic research. Ships will be necessary for collection of subsurface samples over wide areas, as adjuncts to satellites (for ''sea truthing'') and to long-term moorings and drifters (for placement, retrieval, calibration, and validation studies), and for instrument development. For example, the collection of core material and downhole measurements requires sophisticated equipment and an advanced drilling vessel. ODP uses the JOIDES Resolution, which was modified to meet the special requirements of scientific ocean drilling and replaced the drillship Glomar Challenger in 1985. The Resolution has the capability to drill deeper, in more difficult rock formations, and with a more comprehensive set of logging experiments than did the Challenger.
Since the mid-ocean ridges are often located under more than a mile of water, deep-sea research vessels such as the Alvin submersible are required for sampling. The Alvin, which was involved in the discovery of deep-sea hydrothermal vents near the Galápagos Islands in 1977, has made hundreds of dives to vent sites along the global ridge system providing scientists with a unique opportunity to investigate these environments. Remotely operated
vehicles (ROVs) and autonomous underwater vehicles (AUVs) are being used with increasing frequency for undersea observations and sampling. Improved optics, increased power of integrated circuits, new materials, and new sensors have made ROVs and AUVs important tools for oceanography. As new sensors become available and size and power requirements decrease, these unmanned vehicles could provide even greater capabilities. The primary limitation at present is the high cost of sensors.
Natural laboratory sites for long-term, in-depth studies of the seafloor have been established by the Office of Naval Research on the East Pacific Rise and the Mid-Atlantic Ridge. ONR's natural laboratories are located on spreading centers along the mid-ocean ridge system and will yield valuable geological and geophysical data. The value of natural laboratories will increase as the variety of experiments and surveys increases.
Long Time Series
It has been demonstrated that continuous or regular observations of ocean conditions at specific sites must be collected over long time intervals (years to decades) in order to characterize the natural variability of oceanic conditions. Ships cannot provide this kind of monitoring. Long-time-series data for certain ocean surface parameters (wind, temperature, color, sea ice cover) can be collected by satellite sensors, while additional parameters can be measured by in situ sensors. Satellite sensors can observe a specific site with overflights on the order of a few times per week, observations may be limited by cloud cover, and typical sensors last only a few years. It has been difficult to maintain data continuity because of the long lead times for sensor and satellite development and the vulnerability of spacecraft to the federal budget process (satellites are discussed in more detail in the next section).
In situ instrument moorings obviously provide less global coverage than satellites, but can measure conditions repeatedly at one site from the surface to the bottom for months at a time. The major constraints to using in situ instruments for long-time-series observations are the harshness of environmental conditions, limited availability of power, and lack of appropriate sensors for measuring some parameters. Significant advances in sensor development are expected in the next 15 years, but for now the lack of in situ instrumentation is a serious limitation.
Many of the required long-time-series observations will be obtained by the Global Ocean Observing System (GOOS), which is specifically intended to provide ongoing observations of critical variables. Some specialized measurements initiated, developed, and operated by other research programs will eventually be transferred to GOOS (e.g., the TOGA observing systems). Just as the World Weather Watch has provided a background series of observations to enable global scale meteorological research, it is expected that GOOS will provide a background of long-time-series observations for oceanographic and climate-change research. GOOS will also be a vehicle for the development of some of the required instrumentation.
Satellites are an extremely important component of many of the programs described in this report because they provide the only opportunity to observe much of the ocean surface in periods of less than a day. It is impossible to achieve synoptic coverage from ships. However, field measurements must still be carried out at selected locations to correlate remote satellite observations with conditions on and beneath the ocean surface as measured from ships and other platforms. Several of the programs described in this report have been designed to exploit particular satellite sensors for monitoring large-scale conditions occurring coincident with shipboard measurements.
JGOFS will incorporate ocean color image data from the Sea-Viewing, Wide Field Sensor (SeaWiFS), and scatterometer data from the Advanced Earth Observing Satellite (ADEOS) and European Remote Sensing Satellite (ERS-1). Ocean color is related to phytoplankton biomass, whereas the scatterometer measures the scattering of radiation by the ocean surface, which is related to waves, and in turn to wind speed. Estimates of wind and waves are necessary to estimate heat, momentum, and gas (i.e., CO2) transfers across the ocean surface. Wind stress is the primary driving force for the upper ocean circulation. Thus, scatterometer wind observations are needed to test predictive models of ocean circulation and to develop improved data for use in climate models. Sea-surface temperature can be measured by infrared radiometers (for example, on ERS-1) and combined with wind measurements to estimate ocean-atmosphere heat exchange.
The TOGA program and WOCE require satellite measurements of sea-surface topography and winds. The Geodetic Satellite Mission (GEOSAT) demonstrated the ability of altimeters to observe the tropical ocean waves generated by El Niño/Southern Oscillation (ENSO) events and to show changes in surface currents driven by the slope of the sea-surface. The TOPEX/Poseidon altimeter is providing sea-level measurements three times more accurate than those from GEOSAT or ERS-1, although ERS-1 will make measurements to somewhat higher latitudes than TOPEX/Poseidon. The accuracy of the TOPEX/Poseidon altimeter will allow it to play a central role in measuring surface currents and lateral oceanic heat transport. The NASA scatterometer (NSCAT) that will be included on the Advanced Earth Observing Satellite (ADEOS) will be more accurate and will provide data for a greater percentage of the ocean surface than will the ERS-1 scatterometer.
NASA is developing a series of large and small satellite platforms on which to fly ocean sensors, the Earth Observing System (EOS) and Earth Probes. These sensors will measure clouds, rainfall, surface temperature, atmospheric particles, and snow and ice cover. The first Earth Probe satellite will support the SeaWiFS ocean color sensor, followed by the Tropical Rainfall Measuring Mission, which will provide data to estimate heat transfer by evaporation and precipitation of water in the tropics.
Data Management and Availability
GOOS and GCOS will cooperate to develop the next generation of atmosphere-ocean data management systems. The Global Telecommunications System (GTS) was developed for the World Weather Watch and is now showing its age. The new system will be Internet-based and will involve distributed data bases. One significant aspect of the trend toward GOOS and GCOS as major observational programs is their provision of data for the public good. Since most of the data will have real-time or near real-time uses, as well as retrospective purposes in research programs, it is essential that the data be available in real-time, with no restrictions on dissemination and no proprietary periods during which the data are held by a single researcher. The guiding principle is that all data should be, to the extent technically possible, available immediately for use by all. This principle dictates an increasing use of satellite telemetry systems and advanced processing and quality control systems.