National Geographic : 1972 Apr
Far above NOAA 1, two quite different spacecraft hang like silver spiders over the Equator. Known as ATS (Applications Tech nology Satellites) 1 and 3, they do not orbit the earth. Or, more properly speaking, they move just fast enough to keep up with earth's rotation. Thus each always hangs above the same spot on earth, and for this reason they are' called geosynchronous or geostationary. Although the ATS satellites belong to NASA, the Weather Service makes extensive use of their remarkable photographs. From the lofty vantage point of 22,300 miles, ATS cameras can see almost one entire side of earth. This means that at frequent intervals we can take a fresh look at cloud patterns over the United States and over the spawning grounds where much of our weather is born. Heat Pictures Add Vital Data Spectacular though they may be, TV pic tures from space may prove less valuable in the years ahead than information from scan ning radiometers. These instruments are already carried by the NOAA satellites. They detect and measure radiation not only in the form of light, but also in the form of heat the energy of long-wave infrared radiation. Since heat is what drives the great engines of the ocean and atmosphere to produce our weather, that information can be of great value to weather scientists. But we will not be deprived of pictures from space. Radiometer scannings can be converted to images similar to those made by TV cameras. And since the radiometers work with both infrared and visible light, they produce excellent pictures on the night side of earth as well as the daylit side, making 24-hour global coverage possible. David S. Johnson, Director of the National Environmental Satellite Service at Suitland, Maryland, explains the remarkable things weathermen can learn from infrared: "In addition to images, infrared sensing from satellites gives us the temperatures of earth, sea, and clouds, to an accuracy within 3° F. It helps us estimate how high the cloud tops are, and therefore what kind of clouds we are seeing. Moreover, we can interpret the readings to give us a profile of tempera tures at various levels in the atmosphere. This information is absolutely essential for making longer-range forecasts than those now possible.* "Finally, some of the new devices will even measure water vapor at different heights, and 524 others may report on the total levels of such pollutants as dust, carbon dioxide, nitrous oxide, and sulfur dioxide. "These infrared sensors represent a truly great leap ahead for the 1970's." In the latter part of this year a brand-new weather satellite called GOES (Geostationary Operational Environmental Satellite) is scheduled to join the ATS spacecraft 22,300 miles above the Equator. Stationed at 1000 west longitude, over the Pacific Ocean 1,350 miles south of Mexico City, it will be the first of a new series of earth-synchronous weather eyes. Weathermen refer to GOES and ATS space craft as "natural-disaster satellites," because they are so useful in early detection of severe storms. After a polar-orbiting NOAA spots a potential storm, 12 hours must elapse before its spiraling path around the globe brings it back for another look. But GOES, from its steady vantage point, will take a new look every 20 minutes. If a thunderstorm develop ing from cumulus clouds seems likely to pro duce tornadoes, GOES may be able to give warning in time. Satellite Asks Questions of Earth GOES will do something else NOAA is not equipped to do: It will collect weather infor mation from remote stations anywhere in its field of view. Rain and river gauges, drifting buoys, ships, and perhaps balloons and air craft will, on command from the spacecraft, radio their findings directly to GOES, which will relay them to the computers in satellite headquarters at Suitland, Maryland. So capable is GOES, in fact, that it could interrogate as many as 40,000 remote stations every six hours, and send back to earth pic tures containing a maximum of a hundred billion bits of information each 24 hours. Handling the mathematics involved in digest ing such a torrent of information challenges even the fastest modern computers. If all this seems like a great surplus of information, listen to the late John von Neu mann, the celebrated mathematician who nearly a quarter of a century ago pioneered the idea of computers for analyzing weather: "The hydrodynamics of meteorology," said von Neumann, "presents without doubt the most complicated series of interrelated prob lems not only that we know of but that we can imagine." *See "Remote Sensing: New Eyes to See the World," by Kenneth F. Weaver, GEOGRAPHIC, January 1969.