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Spring 1998

UCAR, Taiwan joining forces to launch COSMIC

by Bob Henson
UCAR Communications

A new chapter in the development of GPS/MET (meteorological applications of Global Positioning System satellites) has begun. On 4 December 1997, UCAR signed a planning contract with Taiwan's National Space Program Office (NSPO) and created the newest member of the UCAR Office of Programs: the project office for COSMIC, Constellation Observing System for Meteorology, Ionosphere, and Climate.

With substantial support from Taiwan and close scientific and technical collaboration, the COSMIC team plans to put eight GPS/MET instruments into low earth orbit by 2001--a long-held goal of the system's creators at UCAR. "We are very excited about COSMIC. It's like a dream come true," says Randolph Ware, director of UCAR's University NAVSTAR Consortium (UNAVCO) and one of the leaders behind GPS/MET.

Ying-Hwa Kuo. (Photo by Mariah Carbone.)

Ying-Hwa (Bill) Kuo (NCAR Mesoscale and Microscale Meteorology Division) will work half-time as COSMIC's director. Michael Exner will serve as systems manager, overseeing the constellation's development and collaborating with colleagues at Florida State University, the University of Arizona, the University of Texas at Austin, the University of Alaska, the Naval Research Laboratory, and other universities and laboratories in the United States and Taiwan. A key participant is the NASA/California Institute of Technology Jet Propulsion Laboratory. JPL will provide the prototype design for the GPS/MET instrument (which will be much improved over a version used in the 1995 GPS/MET experiment on the MicroLab-1 satellite) and will contribute to the spacecraft system design. Two other instruments for ionospheric sensing will be included on the COSMIC satellites (see below).

"The role of JPL as a partner in COSMIC is especially important," says UCAR president Richard Anthes. "JPL is the world's leader in radio-occultation science and technology. We hope that the COSMIC partnership will lead to a long-term strategic alliance between JPL and UCAR that will include other joint GPS-meteorology projects beyond COSMIC."

Each COSMIC satellite will intercept GPS signals, which can be used to infer temperature, moisture, and pressure at the tangent point of the ray path. Together, the constellation will span the globe and retrieve as many as 4,000 vertical profiles of the atmosphere each day. The result will be meteorological data at heights up to 60 kilometers (38 miles) and ionospheric data from 100 to 750 km (63-470 mi). COSMIC will demonstrate--for the first time--the usefulness of microsatellite constellations in obtaining global atmospheric "snapshots" in near-real time. The system has the potential to furnish valuable data for weather prediction, global climate change analysis and research, and ionospheric research and prediction. COSMIC data will be available to the international scientific community free of charge, or at the marginal cost of distribution.

A major step toward COSMIC took place in April 1995, when a prototype instrument designed by JPL went into orbit aboard the MicroLab-1 satellite on a mission conceptualized and planned by UCAR's GPS/MET team. Since its launch, the GPS/MET prototype has obtained over 100,000 atmospheric soundings, fulfilling its role as a proof-of-concept experiment.

However, notes Ware, a single satellite "does not offer a large enough number of daily soundings to have an impact on weather prediction and space-weather monitoring." For the data to make a difference in forecast models and other applications, worldwide coverage is needed from an array of satellites. "Four thousand soundings per day, obtained globally in all kinds of weather, should be very useful," says Kuo.

The eight satellites in the constellation will be launched simultaneously in June 2001 and deployed around the globe at an altitude of around 750 kilometers (470 miles). The GPS/MET instrument on each satellite will measure how long it takes for a radio signal (transmitted by a GPS satellite) to enter the earth's atmosphere obliquely, pass through the atmosphere, and reemerge to strike the COSMIC satellite. From this occultation, scientists can infer the density of the atmosphere at the ray's tangent point to the earth and, with other data, the moisture, temperature, and pressure at various heights. The data will then be processed so they can be assimilated by the computer forecast models that guide day-to-day weather predictions.

Two additional instruments will join COSMIC: a tiny ionospheric photometer (to be built at the Naval Research Laboratory) and a tri-band beacon transmitter. These will provide two-dimensional measurements of electron density, an important aspect of the upper atmosphere. These readings will complement the primary GPS/MET instrument so that three-dimensional fields of electron density between 90 and 750 km (55-470 mi) can be inferred. The data could help space-weather specialists to monitor and analyze solar storms. These outbursts inject huge numbers of high-energy particles into the earth's upper atmosphere, jeopardizing power grids and high-frequency communications on earth as well as communication satellites in space.

For the third of four satellite missions planned between 1991 and 2006, the NSPO sought a scientific goal of global importance. Following meetings between Taiwan and UCAR scientists in Boulder in July and in Taiwan in August, the two organizations agreed to collaborate on COSMIC. Since then, says Kuo, "Mutual trust and a close working relationship have paved the ground for COSMIC to develop rapidly."

In late February, NSF and the Taiwanese National Science Council sponsored an international COSMIC science workshop in Taipei. Extensive collaboration will continue after the workshop, according to COSMIC chief scientist Christian Rocken. "Through meetings, e-mails, and the Internet, we hope to establish a virtual COSMIC science center where people can collaborate across the globe," he says.

For more details on COSMIC, contact Sarah Allen (303-497-8647, sallen@ucar.edu) or Kuo (303-497-8910, kuo@ucar.edu).

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