When satellites fail, others fill in; Earth's flexible orbiting weather watchers
Weather forecasters appear to have lost the hawk-eye view of the eastern Pacific Ocean afforded by the US GOES-W satellite. But there are other ''eyes-in-the-sky'' that can help them monitor that important storm-breeding area.
At this writing, the satellite's picture-taking ability seems to be permanently lost, according to Russ Koffler of the National Earth Satellite Service. When the imaging system failed Nov. 25 just after Hurricane Iwa swept over Hawaii, NESS technicians hoped to revive it. That now seems unlikely, Mr. Koffler says.
However, a Japanese weather satellite located farther to the west has a view from Asia to Hawaii. Observers in Hawaii can read pictures from that satellite every three hours. Also, two US weather satellites in near polar orbits give views of the Pacific off the West Coast of the United States four times a day. NESS technicians may also try to revive a retired, seven-year-old GOES satellite that might give daytime pictures of usable but degraded quality.
Although these other satellite views won't fully compensate for loss of the twice-an-hour photos from GOES-W, forecasters should have enough to go on until a new GOES is launched April 28. Whether or not it can be sent up earlier is uncertain because the calendar at Cape Canaveral is tight, Koffler explains.
He also notes that this event demonstrates how well weather satellites have been integrated into both the US domestic and the global weather-watching networks. Their operation is, for the most part, routine. The occasional failure can be worked around.
Domestically, the US Weather Service now relies on a four-unit civilian satellite system.
Two are stationed over the equator in the so-called geosynchronous orbit. They are in an orbit 35,860 kilometers (22,300 miles) high and travel around Earth at the same angular speed with which the planet itself turns. Thus they remain over a given spot on Earth's surface.
At present, these GOES (Geosynchronous Operational Environmental Satellite) units are stationed at longitude 75 W (GOES-East), covering North and South America and the Atlantic Ocean, and 135 W (GOES-West), covering North America and the Pacific to a little west of Hawaii.
Besides taking pictures with visible light and infrared heat radiation, GOES satellites act as communications relays for data transmissions and for reading out instruments on ocean buoys, tide gauges, and other remote, unattended installations. They monitor particles coming from the sun, X-rays, and Earth's magnetic field. Although GOES-W can no longer send pictures, it still carries out these other functions.
The other two satellites in the US system, which are called TIROS (Television and Infrared Observation Satellite), swing around Earth within a few degrees of the poles. They are at relatively low altitudes - 833 km. (518 miles) or 870 ( 541 miles) - in sun-synchronous orbits. Located 90 degrees apart along these orbits, they cover the entire Earth several times a day under preplanned conditions of daylight. Besides giving cloud pictures, they report snow and ice cover and atmospheric temperatures, collect data from remote instrument platforms, and monitor the energies of electrons and protons coming from the sun.
This four-satellite system has become a powerful weather-observing tool for forecasters. It still functions well in spite of losing one GOES image system. Indeed, meteorologists who work with it say it faces a far larger threat from Reagan administration budget-cutters. The administration would like to cut one satellite out of the two-satellite TIROS system. This, meteorologists say, would hamper the effectiveness of the system and risk total loss of polar orbiter data should the remaining satellite malfunction.
For the past two budget years, the administration has proposed cutting out funding for one TIROS, only to have Congress restore it. At the moment, launch of a replacement TIROS is scheduled for March. The fiscal 1983 budget, not yet announced, is expected again to include funds for only one TIROS. US satellite meteorologists are waiting with some concern to see what Congress will do about it.