How COSMIC Works

COSMIC is made up of a constellation of six microsatellites, the first to use radio occultation.
COSMIC is made up of a constellation of six microsatellites, the first to use radio occultation.
Illustration courtesy Orbital Sciences Corporation

Ever wonder why your Global Positioning System (GPS) device sometimes places you in the middle of a building, when you're pretty sure you're still on the street or sidewalk? Frustrating, yes, but the problem is not with the accuracy of the GPS network itself (the GPS satellites' locations are known quite precisely). The problem comes from distortions in the GPS signal caused by the atmosphere around you. Temperature, pressure and humidity in the air -- and even electrical variations in the upper atmosphere -- all have a cumulative effect on the GPS signal by the time it reaches your location.

Turning vice into virtue, COSMIC is a groundbreaking joint project by the United States and Taiwan that listens to the distortion in the GPS signal and calculates information that can be used to improve weather forecasting, predict climate change and monitor the Earth's changing magnetism.


Using a concept developed in the 1960s for the Mariner IV mission to Mars, and based on the success of a preliminary proof-of-concept experiment (Global Positioning System/Meteorology, or GPS/MET) in the late 1990s, the University Corporation for Atmospheric Research (UCAR) in Boulder, Colo., and Taiwan's National Space Organization (NSPO) reached an agreement in 2001 to develop a more robust experimental program. While its official title is the Formosa Satellite Mission #3/Constellation Observing System for Meteorology, Ionosphere and Climate (FORMOSAT-3/COSMIC), it is generally referred to in the United States simply as COSMIC. The NSPO is providing 80 percent of the $100 million funding for the project, with UCAR and other American agencies providing the rest [source: Henson].

Perhaps more interesting than COSMIC's name is what it's proposing to do. Its five-year mission is to show that it doesn't take a lot of resources to provide the kind of fundamental science needed to redefine meteorology and begin building the archive of accurate climatological data needed to improve existing climate models. This in turn will teach us a great deal about climate change.

Ultimately, the observations made by COSMIC could allow us to predict hurricanes, droughts, other major natural disasters and even thunderstorms much more accurately.

Next, let's take a look at the different components that make up COSMIC.


COSMIC Components

COSMIC was launched on April 14, 2006 from Vandenberg Air Force Base in California.
COSMIC was launched on April 14, 2006 from Vandenberg Air Force Base in California.

COSMIC consists of a network of satellites, ground stations and data centers.



Launched on April 14, 2006 on a single Minotaur rocket, the "constellation" of six cylindrically shaped COSMIC microsatellites took between one to two years to reach operational altitude and position [sources: COSMIC Web site, Fong]. Each satellite weighs around 110 pounds (70 kilograms) and measures about 46 inches (116 centimeters) wide and 7 inches (18 centimeters) high, and each one carries the same set of three instruments on board. We'll cover those instruments and what they do a little bit later, but generally speaking, these satellites make detailed measurements across the atmosphere every day.

COSMIC satellites are in a polar orbit, meaning that during each trip around the planet they pass over both poles. Separated by 30 degrees of longitude and operating at about 500 miles (800 kilometers) above the planet, the satellites together are optimized to cover the entire surface of the Earth as often as possible [source: Anthes].

Because the mission approach is new and limited to six satellites, technical problems sometimes arise. At any one time, several of the satellites are experiencing low power or other technical issues, limiting their functionality and the number of observations the instruments on board can make. The projected life of the satellites is five years [source: Fong].

Ground Stations

Data transmitted from the satellites is collected by ground stations in Alaska, Virginia, Norway and Antarctica, with most of the downloading taking place in Alaska and Norway [source: Hunt]. These ground stations then relay the information to the data centers. The Multi-Mission Center (MMC) located in Taiwan controls the movement of the satellites themselves [source: Schreiner].

Data Centers

The data received by the ground stations is forwarded to the data centers in Taiwan and Boulder. In the United States, the data center is called the COSMIC Data Analysis and Archive Center (CDAAC), where a staff of 10 processes and distributes mission data to the scientific community.

But what data are actually collected, and how is this done? The next page explains just what's on board each COSMIC satellite.


The Science of COSMIC

Before we explore the nuts and bolts of COSMIC, it helps to know a few details about the Earth's atmosphere that most of us learned in school but may have forgotten. The atmosphere is not too different from a multi-layer birthday cake, with each layer sitting atop the next, except that inhaling air in the atmosphere won't often give you a stomachache. Also, the dividing lines between atmospheric layers are not nearly as well-defined as layers of creamy chocolate frosting. The lowest level of the atmosphere is called the troposphere. It consists of the air that we breathe every day and is where most of the events we associate with weather take place. This layer goes from the ground up to around 6.2 miles (10 kilometers) above the Earth's surface.

Above that sits the stratosphere, which stretches from approximately 6.2 to 20 miles (10 to 30 kilometers) above the Earth. Originally thought to be very stable, air warming or cooling in the stratosphere is now known to cause significant changes in weather patterns in the troposphere, making this area an extremely worthwhile subject to study [source: Yalda].


The last thing we need to know about is the ionosphere, which consists of the ionized, or charged, particles in the upper atmosphere starting around 50 miles (80 kilometers) above the Earth. Intense solar radiation at this altitude dislodges electrons from molecules in the air, electrifying the atmosphere [source: UCAR]. If you've seen the aurora borealis, you've seen the ionosphere in action.

Now that we have a better understanding of what COSMIC is looking at, let's explore the instruments it uses to get the best view.



COSMIC's low-Earth-orbiting (LEO) satellites intercept GPS radio signals to measure their bend and signal delay as they pass through the atmosphere.
COSMIC's low-Earth-orbiting (LEO) satellites intercept GPS radio signals to measure their bend and signal delay as they pass through the atmosphere.
Illustration courtesy Broad Reach Engineering

One of the more interesting aspects of COSMIC is the way it uses traditional GPS signals that already exist to gather information on atmospheric conditions from around 0.6 miles (1 kilometer) above the ground and higher [source: Schreiner]. Using its Radio Occultation (RO) receiver, the satellite detects a GPS signal as it starts to pass through Earth's atmosphere. Because the COSMIC satellite knows exactly where the GPS satellite really is, it can take the distortion, or refraction, caused by the atmosphere to calculate the temperature, air pressure, humidity and even electron density over a specific spot on the ground.

Each observation using this data results in a "vertical profile" over a specific spot on the ground. These observations are made up to 2,500 times per day, which over time produces a detailed three-dimensional picture of the atmosphere.


COSMIC's onboard Tiny Ionospheric Photometer (TIP) is mapping Earth's ionosphere with more precision than was available previously. It might be tiny, but it also allows continuous observation of the ionosphere at the far ultraviolet 135.6-nanometer wavelength.

Whereas the RO receiver is providing data of a vertical nature (measuring the atmosphere from the ground up three-dimensionally), the TIP instrument is mapping the ionosphere in a horizontal manner, or two-dimensionally [source: Dymond]. The TIP works only at night due to interference caused by solar ultraviolet radiation [source: Anthes].

Also mapping the ionosphere, but providing both horizontal and vertical data, is the Tri-Band Beacon (TBB). The TBB works by emitting a signal directly down from the satellite toward receiving stations, thereby determining the electron density of the ionosphere. A limited number of receiving stations have been set up along the north-south axis of the polar orbit in East Asia and North and South America [source: Anthes].

Working in conjunction with the receiving stations it passes over, and using electron density data from the other two instruments on board, the TBB provides a detailed 3-D model of the ionosphere [sources: Dymond, Bernhardt].

The six RO receivers collect up to 2,500 observations per day when all satellites are operational [source: COSMIC Web site]. The TIP and TBB are scanning constantly and provide continuous coverage.

On the next page, we will look at some of the ways in which the data collected by COSMIC is being used today, and what the future of this program might be.


The Future of COSMIC

COSMIC's primary mission is to prove that using radio occultation and constellations of satellites provides useful data about our atmosphere [source: Anthes]. Already, data from the mission has been used to predict tropical storms more accurately. In 2006, Tropical Storm Ernesto formed in the Atlantic Ocean. Traditional weather prediction models failed to predict the storm's formation, but by adding COSMIC data to the model, prediction's about the storm's formation were very similar to what was actually observed [source: Anthes].

Perhaps even more important is how it can help us understand climate change. As we described earlier, radio occultation measurements create vertical profiles of the atmosphere. Because these measurements do not rely on any specific technology to be interpreted, they are ideal for long-term comparison. On the down side, difficulties separating the different effects of temperature, pressure and humidity limit the usefulness of some of the data below 5 miles (8 kilometers) and above 15 miles (25 kilometers) for climate research [source: Anthes].


Basically, COSMIC is taking a concept beyond the idea stage and showing that this technology can provide useful results. UCAR organizes an annual workshop to allow scientists to share information and learn more about what the data can be used for. The technology and method is not new, but actually having this kind of data available on a large scale is.

COSMIC's two data centers are responsible for providing the information (free of charge) to the international scientific community. As of April 2010, there were over 1,100 users from 54 countries [source: Schreiner]. Scientists use this data to improve their research and learn how to incorporate this type of information into their work more accurately.

Have some atmospheric research you'd like to use the data for? Registration is free on the CDAAC Web site, though you will have to let them know how you're going to use the information.

COSMIC is funded through 2011, with a possibility of continued funding after that [source: Schreiner]. Once the mission concludes, it's not entirely certain what, if anything, will replace it. UCAR and NSPO are both hoping to gain support for a sustained program with two to four times as many satellites doing the same thing, but providing much more complete coverage than is possible with just six satellites. If these hopes are realized, weather prediction could become so accurate that people might just have to find something besides the local forecast to joke about.

For more information on satellites, weather prediction and more, visit the links on the next page.


Lots More Information

Related HowStuffWorks Articles

More Great Links


  • Anthes, R.A. (et al.). "The COSMIC/FORMOSAT-3 Mission: Early Results." Bulletin of the American Meteorological Society. Vol. 89, no. 3. Page 313-333. March 2008.
  • Anthes, Richard A; Rocken, Christian; Kuo, Ying-Hwa. "Applications of COSMIC to Meteorology and Climate." Terr., Atmos. Ocean. Sci. Vol. 11, no. 1. Page 157-186. March 2000.
  • Bernhardt, Paul (et al.). "Atmospheric Studies with the Tri-Band Beacon Instrument on the COSMIC Constellation." Terr., Atmos. Ocean. Sci. Vol. 11, no. 1. Page 291-312. March 2000.
  • Chen-Joe Fong (et al.). "FORMOSAT-3/COSMIC Space craft Constellation System, Mission Results, and Prospect for Follow-On Mission." Terr., Atmos. Ocean. Sci. Vol. 20, no. 1. Page 1-19. February 2009.
  • Constellation Observing System for Meteorology, Ionosphere, and Climate: A Joint Taiwan-U.S. Space Mission for Atmospheric and Geodetic Sciences (2002).
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  • Dymond, Kenneth F. (et al.). "Ionospheric Electron Density Measurements Using COSMIC" (PowerPoint presentation). Session 4, New Data Sources and Products (American Meteorological Society meeting). January 21, 2008. Accessed March 18, 2010.
  • Henson, Bob. "Signal Accomplishments." UCAR Quarterly. Fall 2007.
  • Hunt, Doug. Software Engineer (UCAR-COSMIC). Personal correspondence. March 16, 2010.
  • Rocken, Christian (et al.). "COSMIC System Description." Terr., Atmos. Ocean. Sci. Vol. 11, no. 1. Page 21-52. March 2000.
  • Schreiner, Bill (et al.). "COSMIC Data Analysis and Archive Center (CDAAC): Activities, Ionospheric Research." January 18, 2010. (Accessed March 14, 2010.)
  • Schreiner, Bill (et al.). "COSMIC Data Analysis and Archive Center (CDAAC): Current Status and Future Plans." Fourth FORMOSAT-3/COSMIC Data Users Workshop. October 27-29, 2009.
  • Schreiner, Bill (CDAAC). Personal correspondence. March 17, 2010.
  • University Corporation for Atmospheric Research. "COSMIC (main project Web site)." November, 2009. (Accessed March 14, 2010.)
  • Yalda, Sepideh. Professor of Meteorology, Millersville University. Personal interview. March 25, 2010.