Satellites To Profile Weather, Improve Forecasts Through GPS

A revolutionary, globe-spanning satellite network will furnish round-the-clock weather data, monitor climate change, and improve space weather forecasts by intercepting signals from the Global Positioning System (GPS).

Using atmosphere-induced changes in the radio signals, scientists will infer the state of the atmosphere above some 3,000 locations every 24 hours, including vast stretches of ocean inadequately profiled by current satellites and other tools.

Nearly 100 scientists from over a dozen countries are meeting in Boulder on August 21--23 to help plan the use of data from this $100 million mission, which will begin operations in 2005.

Called COSMIC, the satellite network is now being developed through a U.S.-Taiwan partnership based on a system design provided by the University Corporation for Atmospheric Research, where the COSMIC Project Office is based. Taiwan's National Science Council and National Space Program Office (NSPO) and the U.S. National Science Foundation are providing primary support for COSMIC.

"The increased coverage will improve weather forecasts by providing data where there previously was none or not enough," says Ying-Hwa Kuo, project director for the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC), also called ROCSAT-3 in Taiwan.

With six satellite receivers, COSMIC will collect a global, 3-D data set expected to improve analyses of both weather and climate change. By tracking temperature in the upper atmosphere up to 30 miles high, COSMIC could help clarify whether these regions are cooling due to heat-trapping greenhouse gases closer to the surface.

COSMIC will also measure high-altitude electron density, potentially enhancing forecasts of ionospheric activity and "space weather."

COSMIC's satellites will probe the atmosphere using radio occultation, a technique developed in the 1960s to study other planets but more recently applied to Earth's atmosphere.

Each satellite will intercept a GPS signal after it passes through (is occulted by) the atmosphere close to the horizon. Such a path brings the signal through a deep cross-section of the atmosphere. Variations in electron density, air density, temperature, and moisture bend the signal and change its speed.

By measuring these shifts in the signal, scientists can determine the atmospheric conditions that produced them. The result: profiles along thousands of angled, pencil-like segments of atmosphere, each about 200 miles long and a few hundred feet wide.

Rather than replacing other observing systems, COSMIC will blend with them, filling in major gaps and enhancing computer forecast models. Many satellite-based products are like topographic maps that trace the contours of atmospheric elements in a given height range with high horizontal precision.

COSMIC is more akin to a set of probes that drill through the depth of atmosphere with high vertical precision. Thus, says Kuo, "COSMIC will complement the existing and planned U.S. meteorological satellites."

Radiosondes (weather sensors launched by balloon) have obtained vertical profiles since the 1930s. However, they are launched only twice a day in most spots, and few are deployed over the ocean.

In contrast, the COSMIC data will be collected continuously across the globe. The GPS radio signals can be picked up by the low-orbiting COSMIC receivers even through clouds, which are an obstacle for satellite-borne instruments that sense infrared rays of the spectrum.

UCAR and colleagues began exploring the use of GPS-based observing systems in 1995 with the successful launch of a test satellite. Several other systems have been launched by researchers in the United States, Germany, and Argentina.

All of these are research-based systems, with the data made available within days or weeks. COSMIC's data will be available within three hours of the observations, making them a potential boon to everyday forecast operations. The COSMIC Project Office will serve as a clearinghouse for research use of the data from COSMIC and other GPS-based systems by scientists in the U.S., Taiwan, and elsewhere.

When I watch The Weather Channel for my forecast, it is usually off by 5-10 degrees from what the local weather people predict. As my husband says, it's just a guessing game.

This is a pretty cool application, though the atmospheric "slice" is actually quite thick. The resolution will be better than radiosondes, but still rather coarse.

I'm thinking the mission resolution could be greatly improved by the addition of a large number of ground-based transmitters to serve as a sort of ground-reference truth.

I work with the people who are doing this, and Yuma Proving Ground expects to benifit from this effort. The article has it pretty much right, the major expected effect is to fill in the data gaps that exist over the oceans. This is expected to improve the computer models to improve forecasts.

Computational power is getting so cheap that Linux cluster based supercomputers can be used to improve weather forecasts at the local level. The boundary conditions, though, are still set by the data that comes into the synoptic scale (contenint sized) models run at the national level. Improve the national models, and there is the possibility that we can considerably improve forecasts of winds, for example, down to the township/airport level, say a resolution of a couple of miles. and a couple of hours.

Oops, and I forgot to mention, all made possible by the exploitation of space.. Lets have more, faster, cheaper, better space exploitaiion with free enterprise and competition. It has already started!

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