How scientists at Austin’s Center for Space Research are measuring the loss of water around the world
Every now and then, Byron Tapley steps outside with a pair of binoculars and trains them toward the late afternoon sky, hoping to catch a glint of sunlight reflecting from a pair of minivan-sized satellites he has nicknamed Tom and Jerry.
Tapley has good reason to be proprietary: he leads the team of scientists who launched the twin satellites in 2002. Working in tandem, the satellites orbit the earth from pole to pole every 90 minutes, recording tiny variations in the earth’s gravitational field caused by the movement of vast amounts of water. The two spacecraft have provided compelling evidence for a rapidly changing planet: shrinking glaciers and ice caps, rising ocean levels and depleted aquifers.
Tapley heads the Center for Space Research at the University of Texas at Austin and also serves as principal investigator for the satellite project, formally known as the Gravity Recovery and Climate Experiment - GRACE. A collaboration with NASA’s Jet Propulsion Laboratory and the German space agency, GRACE has been a spectacular success, providing a decade’s worth of important data for hundreds of hydrologists, oceanographers, geographers, and glaciologists. “It’s the best thing and the most fun that I’ve done,” says Tapley, 78, a courtly man with wide-set blue eyes who views the project as the crowning achievement in a lifetime of aerospace research. “It’s a great way to finish it up.”
Jay Famiglietti, director of the Center for Hydrologic Modeling at the University of California, Irvine, believes GRACE is helping to transform climate science. Using GRACE measurements, for example, he and his colleagues have shown that aquifers are being depleted in northwestern India and in California’s Central Valley as farmers pump more water in response changing rainfall patterns. “The GRACE data has really revolutionized our understanding of how water is stored across the continents. It’s given us a global picture of what I call real water use, as opposed to something that’s based on statistics,” Famiglietti says.