If all goes well, the COSMIC six-satellite array will be launched today at 5:10 PM PDT by a Minotaur rocket from Vandenberg Air Force Base. The $100 million constellation will use the U.S. Global Positioning System (GPS) signals to track hurricanes, climate change, and space weather. And these satellites will rely on a technology called radio occultation to measure the bending of GPS radio signals as they pass through Earth's atmosphere. This should vastly improve our knowledge of space weather, including geomagnetic storms that can disrupt satellite and communications systems.
Before going further, here is an artist's rendition of the six microsatellites which will form COSMIC when they are on orbit (Constellation Observing System for Meteorology, Ionosphere, and Climate) (Credit: Orbital Sciences Corporation). And here is a link to a larger version of this illustration.
Here are some details about these microsatellites.
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.
As I mentioned above, this constellation of satellites will use a technology known as radio occultation. But what is this technology?
Just as the water molecules in a glass change the path of visible light waves so that a pencil appears bent, molecules in the air bend GPS radio signals as they pass through (are occulted by) 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.
Below is a diagram showing the concept of radio occultation (Credit: Broad Reach Engineering). Here is a link to a larger version.
When radio signals from GPS satellites pass through the atmosphere, the signals' paths are bent and their progress is slowed. The rate of these changes depends on the atmosphere's density along the path. COSMIC's low-Earth-orbiting (LEO) satellites take advantage of this effect by intercepting the GPS radio signals just above Earth's horizon and precisely measuring the bend and signal delay along the signal path.
And what can we expect from this US-Taiwan collaboration?
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 should be a boon to scientists quantifying long-term climate change trends.
And now, let's cross our fingers and hope for a successful launch.
Sources: National Science Foundation news release, via EurekAlert!, April 12, 2006; and various web sites
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