The low-orbiting satellites will be the first to provide atmospheric data daily in real time over thousands of points on Earth for both research and operational weather forecasting. The satellites will measure the bending of radio signals from the U.S. Global Positioning System (GPS) as the signals pass through Earth's atmosphere.
Called COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate) in the United States and FORMOSAT-3 in Taiwan, the $100 million satellite network is the product of an agreement between the American Institute in Taiwan and the Taipei Economic and Cultural Representative Office in the United States. The array is based on a system design provided by the University Corporation for Atmospheric Research (UCAR).
Temperature and water vapor profiles derived from the GPS data will help meteorologists observe, research, and forecast hurricanes, typhoons, and other storm patterns over the oceans and improve many areas of weather prediction. The stability, consistency, and accuracy of the measurements will provide critical new information to scientists quantifying long-term climate change trends, say atmospheric scientists.
COSMIC's measurements also will improve analysis and forecasting of space weather--the geomagnetic storms that can interrupt sensitive satellite and communications systems and affect power grids on the ground.
"The satellites will convert GPS measurements into a precise worldwide set of weather, climate, and space weather data," said Jay Fein, program director in the U.S. National Science Foundation's Division of Atmospheric Sciences, which funded COSMIC. "The resulting new information will have a tremendous impact on geosciences research and weather prediction, and will be an important contribution to global Earth observations."
COSMIC relies on a technology known as radio occultation. Just as the water molecules in a glass change the path of visible light waves, molecules in the air bend GPS radio signals as they pass through the atmosphere. By measuring the amount of this bending, scientists can determine underlying atmospheric conditions, such as air density, temperature and moisture, and electron density.
"This is the first time the technique of radio occultation has been used on a large scale in real time to provide nearly continuous measurements of worldwide atmospheric conditions at all altitudes," said William Kuo, director of the UCAR COSMIC office.
While several single-satellite systems have used GPS signals experimentally over the past decade, COSMIC's unique six-satellite array is the first to provide the high-density global coverage required for both research and operational forecasting.
"Centers around the world will have access to this new information for both research and operational forecasting," said UCAR president Richard Anthes. "User-friendly versions of the data will enable those with less sophisticated systems to benefit as well."
Orbiting at an altitude of 500 miles (800 kilometers), COSMIC satellites will take approximately 2,500 measurements every 24 hours in a nearly uniform distribution around the globe. The system will provide novel and independent data over vast stretches of the oceans where there are no weather balloon observations. The data's high vertical resolution will complement the high horizontal resolution of other weather satellite measurements.
Because the satellites' radio signals pierce thick cloud cover and precipitation, weather conditions will not interfere with data gathering, as is often the case for remote sensing platforms. The satellites will not need to be recalibrated and the instruments' accuracy and sensitivity will not change during the five-year mission--common problems with Earth-observing satellites over their lifetime. The data will be available to researchers and forecasters within a few hours of the observations.
"The COSMIC mission would not have been possible without the broad support of U.S. sponsors and the partnership with Taiwan," says Fein.
Taiwan's National Science Council and National Space Organization provided more than $80 million for the system. The U.S. National Science Foundation, lead agency for COSMIC science activities, and its partners provided the rest of the support. Major partners include NASA, NOAA, the U.S. Air Force Space Test Program, the Office of Naval Research, and the Department of Defense Space and Missile Systems Center's Rocket Systems Launch Program of the U.S. Air Force, which provided logistical support.
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