Wednesday, December 13, 2006

Grace Works

Grace (Gravity Recovery and Climate Experiment is a wonder, and will, after studying its data, truly begin to offer concrete information, on a much broader scale, about so much that is now conjecture.

'Amazing' tool tracks earth's tiny changes
Twin satellites help in study of ice melts, earthquakes
By Carrie Peyton Dahlberg - Bee Staff Writer
Published 12:00 am PST Wednesday, December 13, 2006

Linked by a constant stream of microwave signals, a pair of satellites have been taking Earth's measure in a way the planet has never been measured before.

By tracking tiny changes in gravitational pull, the system known as the Gravity Recovery and Climate Experiment, or GRACE, has been refining our understanding of polar ice melts and massive earthquakes.

Now, researchers are also improving the system's ability to monitor the way groundwater moves around the globe, so it can spot places where thirsty populations are draining aquifers faster than they can be replenished.

In addition, "we are starting to look very carefully at California," to see what the new technology might reveal about Sierra snowpack, said Jay Famiglietti, an earth system science professor at the University of California, Irvine. Later, he plans to turn his focus to the state's groundwater.

Famiglietti is one of many GRACE fans -- few can resist tossing around the word "amazing" to describe it -- who are gathering this week at the American Geophysical Union fall meeting in San Francisco to talk about what the system can accomplish.

"We have a new tool that can get at this completely hidden thing in the earth, and the sky's the limit in terms of applications," said Michael Watkins, project scientist for the system at NASA's Jet Propulsion Laboratory in Pasadena.

Launched in 2002, what GRACE tracks best is change -- the way the Earth's gravitational pull in the exact same spot varies from month to month.

Water is the biggest factor that changes in such a short time frame, once analysts eliminate little distractions like the weather (a high pressure system will yank at a GRACE satellite a bit more than a low pressure one).

"Water weighs a lot. As water slogs around the Earth, we track it in any form. Water in the form of ice, in the ocean, in the ground," Watkins said.

Even before the satellites went up, Watkins and others anticipated GRACE would be able to measure how quickly polar ice is melting. It came through, producing data earlier this year on the dwindling of Antarctic ice and faster-than-expected losses in Greenland.