Satellite to tell what's blowing in the wind

By , Staff writer of The Christian Science Monitor

Sometime in the 1990s a satellite is expected to be circling the globe which will pulse laser beams toward Earth almost continuously. The target won't be Soviet missiles, but billions of microscopic particles suspended in the atmosphere.

The aim: to measure the wind.

Gauging the direction and speed of this natural force has been diligently pursued since as early as 100 BC, when the Greeks first devised crude instruments. But despite the leaps in meteorological measurement since then, much work remains to be done.

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Now scientists at the National Oceanic and Atmospheric Administration (NOAA) are working on a concept that they believe could dramatically boost the science of wind measurement - and thus prove a boon in several areas:

* Weather forecasting. Meteorologists are getting better at short-term weather predictions. But the longer-range forecasts of eight to 10 days remain ballpark guesses. One reason is the lack of information about global wind patterns. With the space-borne sensor, scientists believe they will be able to glean enough new knowledge about the effect of wind on ''atmospheric dynamics'' to improve both weather and storm prediction for the purposes of:

* Airline routing. Scientists calculate that airlines could save as much as $ 1 billion a year worldwide in fuel costs - $200 million in the United States - by altering flight paths to take advantage of tailwinds and avoid headwinds. Some strides are being made in this area. But dramatic fuel savings won't come until there is better information about upper-atmosphere wind currents.

* Marine forecasting. Of all the regions where reliable wind data prove the most elusive, the oceans rank high. One reason: There is no network of ground sensors, as on land, to gather the information. Scientists contend the proposed ''windsat'' satellite system would fill this gap and could help shippers avoid storms.

At present, high-altitude wind measuring is done largely with balloons. More than 500 are sent aloft around the world every 12 hours. They give good readings over land but little information over water. Other data are gleaned from satellites through temperature readings and photos of cloud movements. But where the clouds are scarce, so are the data. Airline pilot reports are another source of information. Ground-based sensors fill in low-altitude and localized readings. This leaves scientists with many pieces but not the whole puzzle.

The windsat system is seen as going a long way toward rounding out a global wind profile. It would work by pulsing a laser at least twice a second from the satellite down to Earth. The beams, invisible to the human eye, would bounce off windborne tracers in the atmosphere, such as dust particles. Sensors would measure the reflected radiation to gauge wind speed and direction.

In theory, the infrared beams would give readings at 15 atmospheric levels. Shooting from the ground up with a similar system, NOAA scientists have been able to obtain wind measurements up to altitudes of 90,000 feet. ''To achieve a quantum jump in weather forecasting, we feel global wind measurements are going to have to be done,'' says Dr. Freeman Hall, a scientist at NOAA's environmental research lab in Boulder, Colo. ''We feel this is the only method for doing that in the future.''

Maybe so, but it probably won't be until the early 1990s that windsat will be sent aloft, if at all. Daunting technological hurdles remain.

For one thing, a laser has to be developed that can be put in space. It will also have to blink beams long enough to make the venture economical. RCA Corporation, in a recent study, concluded that the wind sensor could be fitted onto a modified version of NOAA's current polar-orbiting weather satellites, the TIROS-N. Estimated cost: $154 million (not including launching).

Given the federal government's desire to get out of the weather satellite business, drumming up funding for such a long-range research project won't be easy. ''It would be the most sophisticated - and expensive - weather sensor ever put on a satellite,'' Dr. Hall says, pointing up both its potential and its major drawback.

More research also has to be done to see if there are enough ''tracer'' particles around the globe to make readings. In the meantime, advanced ground-based sensors are being developed, such as a new generation of microwave systems. Conceivably these will fill the gaps in wind detection. But some scientists still see a windsat, or something like it, as the ''ultimate'' sensor.

''Windsat looks to be at least 15 years away,'' says Dr. David Atlas, chief of atmospheric sciences at NASA's Goddard Space Flight Center, who was at first a skeptic but is now a believer. He calls it ''a revolutionary step in space science and satellite meteorology.''

If windsat ever does see orbit, it would please meteorologists in particular. For the wind has been gaining in importance as a factor in global weather forecasting.

Wind has always been recognized as an important yardstick in predicting regional weather cycles, as well as general climatic activity in the tropics. But recent tests at NASA's Goddard center suggest that it may now be the key to understanding large-scale weather systems everywhere. Preliminary evidence indicates that wind may prove to be a more important weather indicator than surface pressure and temperature - a point certain to be debated among meteorologists.

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