A new tool for atmospheric studies

A rooftop GPS receiver A GPS receiver on the roof of the Mesa Laboratory at the National Center for Atmospheric Research in Boulder, Colo. The University Corporation for Atmospheric Research uses data from cGPS stations to infer atmospheric properties, including temperature, pressure and water vapor. Credit: Copyright University Corporation for Atmospheric Research

Scientists are putting GPS to work in some unexpected new ways. For example, John Braun, a project scientist at the University Corporation for Atmospheric Research (UCAR) in Boulder, Colo., is using GPS to measure precipitable water vapor.

Because atmospheric conditions affect the radio signals from GPS satellites, calculations to determine the position of a GPS receiver include models of the ionosphere and troposphere. Mike Jackson, a geophysicist at Trimble, a manufacturer of advanced positioning solutions that include GPS equipment and software, says it’s possible to turn the calculations around to determine the atmospheric conditions through which the radio waves traveled.

“GPS provides a very well-defined signal,” Braun says. “Because it has a huge amount of infrastructure in place, GPS is very suitable for atmospheric measurements. It provides a temporal and spatial resolution that we can’t get from other methods.”

Braun uses data from more than 500 cGPS stations in the U.S. to create integrated observations of atmospheric conditions, including temperature, pressure and water vapor, through the entire atmospheric column from near Earth’s surface up through the troposphere and stratosphere. Atmospheric researchers use these data to evaluate and improve the accuracy of numeric weather models, to study water cycles on timescales ranging from minutes or hours to years, and to understand processes related to storms.

“Water vapor is difficult to measure because it is so variable, yet it drives almost all of the short-term heavy weather events,” Braun says. “GPS is really well suited to this science.”

John Stenmark

Stenmark is a writer and consultant with more than two decades’ experience in the use of advanced technologies for surveying, geodetic and engineering applications. He can be contacted at john@stenmark.us.

Wednesday, April 30, 2014 - 03:00

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