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acted on a request from NOAA's National Weather Service to interrogate one of these buoys on a daily basis to obtain operational > weather forecasts for the Alaska region.

In response to requests from several State and academic organizations, NASA's Langley Research Center in Virginia fabricated several free-drifting buoys for studies of water movements near the mouth of Chesapeake Bay and along the Virginia coastline. The weight of the buoys was kept below 500 pounds to facilitate their deployment by small ships or helicopters. Techniques originally developed for the tracking of spacecraft were applied to the tracking of the buoys. The buoys are of three general types, classified in terms of the systems used to track their movements: radio buoys, radar buoys, and satellite buoys.

Radio buoys were used by the Virginia Institute of Marine Sciences (VIMS) to study the flow of nutrients through barrier island inlets, the flow of fresh water in Chesapeake Bay during the aftermath of hurricane Agnes, and the drift of shelf water. The movement of the buoys was tracked from an aircraft.

Radar buoys were used to obtain information on the circulation of water around Newport News Point for the Virginia Department of Highways for use in the planning of the second James River bridgetunnel crossing. Radar buoys were also used by NOAA to study the influence of water movement on the formation of near-shore sand ridges. These buoys carried active radar transponders to permit tracking with a portable van-mounted radar system on shore.

Satellite buoys are being used by VIMS and the Woods Hole Oceanographic Institution to study continental shelf circulation. These buoys are equipped with transponders that work in conjunction with a platform tracking and data collection system on the French EOLE satellite which was launched by NASA. The most productive use of free drifting buoys and the EOLE satellite was made by NOAA's Atlantic Oceanographic and Meteorological Laboratories in Miami, Florida. A group of buoys placed in the Sargasso Sea operated successfully for periods of up to eight months and provided previously unavailable information on the extreme variability of surface currents in the ocean. Analysis of the results indicate that if a real coherence between current measurements at sea is expected, the measuring devices can be no farther apart than 150 km. During the sixth and seventh months of this experiment one of the buoys drifted to the Mid-Ocean Dynamics Experiment (MODE) area and provided an unexpected dividend to that project. The transponders used in all of these experiments were loaned to NASA and NOAA by the French space agency.

Technology development in spaceborne systems for positionlocation and data collection has advanced to the point where it will be possible to produce buoy transponder packages weighing one to two pounds with an operational lifetime of several months. Such a

package is planned for use with Nimbus-F, scheduled for launch in 1974. It will be possible, at that time, to track the movement of more than one hundred drifter buoys.

Marine Remote Sensing

Information on water color, sea surface temperature, sea surface roughness, and sea and fresh-water ice can be obtained remotely by means of sensors that respond to the visible, infrared, and microwave portions of the electromagnetic spectrum. Since no one remote-sensing technique is capable of measuring all these parameters, it is necessary to use an optimum mix of remote sensors with appropriate spectral and spatial resolution capabilities.

Considerable advances have been made in the development of multi-spectral visible remote sensors and their utilization on aircraft and satellites. Examples of such sensors are conventional cameras with different lens-filter-film combinations, television cameras with a variety of filters, and multi-spectral scanning radiometers. Data obtained with these remote sensors have been used to monitor ocean current boundary movements, delineate upwelling regions, identify regions with high bioproductivity, map contours of shallow-water bottom features, monitor the dispersal of slicks associated with oil spills and dumpings of acids and sewage sludge, and map coastal zone features.

The state of the art of infrared remote sensing has reached a stage of development where it is being used on operational NOAA satellites and NASA research and development satellites to provide thermal images depicting variations in sea surface temperatures. The newer remote sensors are providing sufficient spatial resolution to permit observations of current eddies, convergences and divergences, and water mass dynamics from satellite altitudes. Airborne infrared remote sensors are being used to monitor the heated water discharged by power plants into rivers and estuaries. At this time the remote sensing of ocean water color can be accomplished only during daylight when the ocean surface is not obscured by haze, fog, or clouds. Depending on the choice of spectral bands, some infrared remote sensors cannot be used at night or at times of adverse weather conditions. To overcome this kind of operational constraint, NASA is now placing emphasis on the development and testing of passive and active microwave remote sensing techniques. Passive microwave remote sensors have the potential to provide information on sea surface temperature and sea roughness, and possibly information about ocean surface wind speeds and directions. Passive microwave scanning radiometers have been found to be useful in delineating the boundaries of sea ice and the distributions of new ice and multi-year ice in the Arctic region. These observations were made from aircraft altitudes.

Active microwave remote sensing techniques are under development and test to determine the feasibility of employing these techniques on aircraft and satellites for accurate measurements of the dynamic topography of the ocean surface, mean sea level, sea state and sea ice conditions, and sea surface wind speeds and directions. A vital part of these development programs is the recognition of the need for "sea-truth" data, independent observations of the sea state conditions from ships or off-shore ocean platforms required for correlation with the output signals from the remote sensor instruments.

A new sensor system is also being developed for use in the Coast Guard's program of aerial pollution surveillance for oil and hazardous substances. This program involves twice-weekly aerial flights over U.S. territorial waters and the contiguous zone, and random flights over prohibited zones as designated by the Convention on the Prevention of the Pollution of the Sea by Oil, as amended. In port areas handling over 10 million tons of petroleum per year, and in other designated areas, daily aerial flights are conducted over the harbors and at least ten miles out over the approach channels.

The Coast Guard is supporting the development of an advanced all-weather, day-night aerial oil-pollution surveillance system to be used in this program. The system will integrate infrared and ultraviolet scanning photometers with side-looking radar and dualfrequency passive microwave radiometers to detect oil slicks and map their extent and thickness. The Transportation Systems Center of the Department of Transportation is also developing an airborne laser-excitation device for the Coast Guard to permit determination of the type of spilled oil.

Aircraft Platforms

Aircraft play an important role as platforms from which experiments are carried out in the field to establish the feasibility or determine the utility of employing various types of remote sensing techniques to obtain information on marine parameters, processes, and phenomena. Over 50 aircraft remote-sensing missions were flown in 1972 by the four aircraft operated by the NASA Johnson Space Center. Thirty-five of these missions were in support of coastal zone experiments dealing with the use of remote sensing in pollution studies in bays, estuaries, and nearshore areas. Sixteen of the aircraft coastal-zone missions were in support of Earth Resources Technology Satellite (ERTS-1) investigations: six were flown over the Great Lakes area to evaluate the performance of passive microwave remote sensors as lake ice monitors, and six were flown over the North Atlantic Ocean and the Gulf of Mexico to support the acquisition of sea-state data with passive and active microwave sensors. An ocean-color mission was flown over the eastern Gulf of

Mexico in support of an ERTS-1 investigation of the Mississippi Sound.

A C-54 aircraft operated by NASA's Wallops Station was used to support several cooperative experiments with the U.S. Navy, the Army Corps of Engineers, the U.S. Coast Guard, the Environmental Protection Agency, the University of Delaware, and the Virginia Institute of Marine Sciences. These efforts were concerned with uses of passive microwave radiometers and multi-spectral band cameras to measure the amount of oil in slicks associated with oil spills. Photography delineated the boundary of the spills; the microwave radiometers provided temperature variations which could be correlated with the variations in oil thickness.

A joint experiment was carried out by NASA and Navy investigators using the Naval Research Laboratory narrow-pulse radar altimeter on the NASA Wallops aircraft to obtain sea roughness measurements. Comparison of the radar altimeter with measurements of sea-state conditions made with an accurate laser profilometer on the aircraft indicated that the use of a narrow-pulse radar system as a remote sensor for sea state measurements was feasible.

Low-altitude aircraft missions were flown over Chesapeake Bay and Lake Ontario in support of performance evaluation tests of a laser remote-sensing system designed by NASA's Wallops Station to obtain measurements of algae and phytoplankton concentrations at and near the surface of the water. The measurement technique makes use of an intense pulsed laser beam to excite fluorescence emissions and a detector to measure the strength of the emissions, which should be proportional to the concentration of the algae and phytoplankton. The data obtained were compared with surface data provided by the Environmental Protection Agency (EPA) and by NOAA.

The NASA Ames Research Center Convair 990 jet aircraft carried out flights in the Arctic region in support of experiments to assess the utility of a passive microwave scanning radiometer as a near allweather sea-ice remote sensor. Missions were flown during March 1972 to take advantage of the presence of scientists on sea ice who were participating in the AIDJEX pilot experiment in the Beaufort Sea. Measurements were made on a day when visibility was good and on a subsequent day when the surface of the ice was obscured by clouds. The capability of employing passive microwave radiometers to obtain information on the spatial and time variations of the distributions of first-year and multi-year ice under virtual allweather conditions was verified by comparison with information on sea-ice conditions provided by the AIDJEX scientists. A series of Convair 990 flights over the Great Lakes during early spring demonstrated the ability of the passive microwave radiometer to map the distribution of fresh-water thin ice and thick ice.

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The Convair 990's high-altitude and performance capabilities were used to advantage in carrying out a number of missions during July 1972 to obtain quantitative data on the effects of atmospheric effects on remote measurements of water color. These data were obtained with a number of precision spectrometers and multispectral scanning spectrometers on the aircraft as it flew specific ground tracks at altitudes of about 45,000 feet and at 1,000 feet. Flights were coordinated with the work of scientists at sea who obtained pertinent "sea-truth" data on water color, turbidity, and chlorophyll concentrations. The data from these missions are being used in defining design and performance characteristics for ocean color remote sensors for planned satellite missions.

The NASA Convair 990 aircraft participated in a joint US/USSR experiment over the Bering Sea early in 1973. The aircraft served as a platform for visible and passive microwave radiometer remote sensors which obtained data on sea ice properties, sea state, sea

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This passive microwave image of Arctic sea-ice was made from the NASA CV 990 aircraft. The dark area represents ice formed several year earlier.

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