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September 2004

A COSMIC project

UOP’s COSMIC office prepares to send six satellites into orbit. The satellites may lead to major breakthroughs in our understanding of climate and the atmosphere.

Chris Rocken (left) and Bill Kuo display an older model of a COSMIC satellite.

In an empty room on the third floor of FL4, two round pieces of metal about the size of small coffee tables lean casually against the wall. Residents of the building have been packing and moving to new offices over the past few months. To someone walking down the hall, it looks like the metal pieces are probably scraps left for recycling.

Far from it. The pieces are models of satellites about to make the trip to space. A year or so from now, six of them will be in orbit. “We’ll take the six of them and stack them up together like pizza boxes, put them on a Minotaur rocket, and launch them into space,” says Bill Kuo with obvious excitement.

Bill is director of COSMIC, a UOP program that stands for Constellation Observing System for Meteorology, Ionosphere & Climate. For the last seven years, he and his colleagues have been getting ready to launch the satellites, which are expected to make a very significant contribution to the atmospheric science community.

“COSMIC will provide invaluable data about the atmosphere,” says UCAR president Rick Anthes, “It has the potential to lead to major breakthroughs in weather forecasting, climate monitoring, and space weather research.”

COSMIC will employ radio occultation, a method that’s never been tried before on such a scale, to retrieve data from parts of the atmosphere that scientists normally don’t access. By taking approximately 2,500 atmospheric measurements every 24 hours in a nearly uniform distribution around the globe, COSMIC’s coverage will easily surpass traditional weather balloons and monitoring stations. As Chris Rocken, COSMIC’s chief scientist, says, “It’s going to be really exciting when this all works.”

Scientists and researchers will access the data free of charge on the COSMIC Web site. COSMIC will provide real-time products for weather forecasting to global weather centers via the Global Telecommunications System, a network of meteorological telecommunication centers.

COSMIC's satellites will provide considerable information about the atmosphere. This map shows the typical locations of a day's worth of COSMIC soundings (diamond shapes) and the locations of radiosonde sites (red circles).

 

Final preparations

With about a year and a half to go until launch, scientists and engineers are busy with the integration and testing of COSMIC satellites. A company in Virginia, Orbital Sciences Corporation, built the first satellite for the UCAR-designed mission. As part of a U.S.-Taiwan partnership, the Taiwanese National Space Program Office is currently assembling and testing the remaining five satellites at its facility in Taiwan. UCAR COSMIC staff in Boulder are finalizing development of an initial version of data processing software for analysis and archiving. They’re also testing the instruments that will fly on the satellites; this includes taking the satellite model onto the roof of FL4 to test its antenna and observing how solar panels affect its performance.

Because COSMIC will provide atmospheric soundings with unprecedented accuracy, vertical resolution, and coverage, its staff feel strongly about the need to prepare the atmospheric science community for the data’s arrival. “At this stage, our key emphasis is getting the scientific community ready to use the data to its full potential,” Bill says.

To this end, the COSMIC Project Office and the Advanced Study Program jointly hosted a summer colloquium for grad students and postdocs on atmospheric remote sensing using GPS. The colloquium included a field trip to Taiwan, where participants watched satellite engineers work on the COSMIC satellites. In addition, scientists here at NCAR (particularly in MMM, CGD, and HAO, due to their emphases on weather, climate, and space weather, respectively) are preparing for the influx of useful new data.

Staffers are also thinking about what Bill calls “life after COSMIC,” since the lifespan for small satellites is only about five years. Europe and China are developing GPS-like systems of their own, so a next-generation COSMIC could potentially receive even more satellite signals. There’s also the possibility of designing micro-satellites that employ a new technology called cross-link, in which the satellites transmit to each other in addition to receiving signals from the GPS satellites.

And, finally, staffers are getting a bit nervous. Space, after all, is risky business. “You basically put very sophisticated instruments on a missile, launch it into space, and just hope it works like a charm,” Bill says. Or as Chris explains it, “Usually in science, you can try something once and then do it again. This is a completely different level of risk than what most scientists are usually dealing with.”

Despite the uncommon risk, Chris says the project is especially rewarding because researchers don’t often get to work on something that could impact everyone on the planet.

“I really can’t wait for the six satellites to be up there and all working,” he says.

• Nicole Gordon

 

What is radio occultation?

The science behind COSMIC originates with a method called radio occultation that was developed in the 1960s to study other planets. More recently, scientists have begun to apply radio occultation to Earth. The method works by taking advantage of radio signals broadcast from Global Positioning System (GPS) satellites already in orbit. The U.S. Department of Defense maintains about two dozen satellites approximately 20,000 kilometers (12,400 miles) above Earth to facilitate civilian and military navigation technology. When people use GPS receivers, they pick up signals from some of these satellites to determine their exact longitude, latitude, and elevation.

As radio signals from the GPS satellites pass through the atmosphere, molecules and electrons bend their paths and slow their progress. COSMIC takes advantage of this effect by intercepting the radio signals and measuring their bend and signal delay. The satellites will then downlink the data at ground stations in Fairbanks, Alaska, and Kiruna, Sweden. Once the data are relayed back to the COSMIC office in Boulder, scientists will retrieve atmospheric profiles of bending angles, refractivity, ionospheric electron density, temperature, water vapor, and more from the raw measurements of the GPS signals.

By intercepting signals in a web around the planet, COSMIC will provide a homogeneity of coverage, especially over the oceans and other areas traditionally sparse in data, that operational weather balloons and monitoring stations can’t match. Its profile will start near Earth’s surface and extend to the height of the COSMIC satellites at 800 kilometers (500 miles) above Earth. (See image above)

“Progress in many fields of research is hindered by lack of good data,” Bill says. “It’s really exciting that we’ve shown that the GPS radio occultation technique works and can potentially have major impacts on weather forecasting, climate monitoring, and space weather prediction.”

Rick points out that UCAR demonstrated the potential of using radio occultation to sound Earth’s atmosphere in the GPS/MET experiment from 1995 to 1997. COSMIC will build on GPS/MET and subsequent radio occultation missions to produce real-time soundings that will be tested for their application to operational weather prediction models.

“The independent nature of radio occultation soundings make them highly complementary to other atmospheric sounding systems,” such as infrared and microwave sounders, Rick says. “Two or three independent sounding systems, when combined properly, can yield atmospheric soundings of temperature and water vapor with higher accuracy and vertical and horizontal resolution than any one system alone.” • Nicole Gordon

On the Web:

For more about COSMIC: www.cosmic.ucar.edu


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