Tokyo

A Taiwan–US collaboration is hoping that its constellation of microsatellites equipped with Global Positioning System (GPS) receivers will provide a valuable new approach to meteorology, climatology and research into 'space weather'.

Most weather forecasting currently relies on balloons that take readings such as temperature and humidity on their way up from some 900 locales worldwide. But these points are restricted to land, ruling out truly global weather models. Weather satellites give wider coverage, but they gather data by looking straight down to Earth, yielding little information about what is happening at various different altitudes.

But the Taiwan-led Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) could change that by using an array of microsatellites and a novel technique to improve the coverage and accuracy of data collection.

Saturation coverage: six microsatellites will improve the coverage and accuracy of climate data. Credit: NSPO

The six COSMIC microsatellites, scheduled to be launched in mid-2005, will pick up radio signals from 28 existing GPS satellites as they pass through the Earth's atmosphere. The microsatellites will observe the refraction (or bending) of the signals, and infer information about atmospheric density from it, at all altitudes. From the density data, researchers will be able to deduce the pattern of pressure and temperature.

“We can also calculate atmospheric moisture near the surface, construct pressure contours, and derive wind fields and other critical quantities,” says Tom Yunck of NASA's Jet Propulsion Lab (JPL), which did much of the early work on the technique.

The most important advantage is coverage. “The microsatellite constellation will measure some 4,000 points spread uniformly around the globe, with high accuracy,” says Chao-Han Liu, president of Taiwan's National Central University.

Researchers on 'space weather' are also excited about the project, says Liu. In the ionosphere, at altitudes of about 80 km, electron density can be measured in a similar fashion to the atmospheric density. This will provide valuable information for predicting magnetic storms, which can affect the operations of satellites and power grids.

The COSMIC system has the potential to significantly improve climatological measurements, says Alan Thomas, director of the Global Climate Observing System secretariat. However, he warns that it will probably take time to develop a reliable system that produces measurements for climate-change applications, and another 20 years or so after that to obtain a meaningful long-term climate data set.

The agreement to build the system, signed on 3 May, involves Taiwan's National Space Program Office (NSPO), JPL, the US University Corporation for Atmospheric Research in Boulder, Colorado, and several US universities.

Taiwan will pay US$80 million of the estimated US$100 million total project cost and will build the satellites with the help of Orbital Sciences Corporation of Dulles, Virginia, which made a prototype version of the satellite in 1995 for a 'proof-of-concept' experiment. Taiwan will also operate the mission.

“This is a chance to get people really interested in space science,” enthuses Luo-Chang Lee, director of NSPO.