Gravity Recovery and Climate Experiment
NASA’s Gravity Recovery and Climate Experiment (GRACE), launched in 2002, is designed to measure the Earth’s gravity field to detect fluctuations in various areas of the planet’s surface. The mission consists of two satellites, nicknamed Tom and Jerry because they chase each other around the globe, which measure about ten feet long. Both are circling in identical orbits about 250 miles above the Earth’s surface and are traveling about 130 miles apart.
Variations in the speed of the satellites, resulting from small fluctuations in the gravitational force of the areas over which they are passing, are measured, and from that information, researchers can calculate the gravitational force which caused the variations. Microwave instruments measure the distance between Tom and Jerry accurately enough to detect variations less than one percent the width of a human hair. Michael Watkins of NASA’s Jet Propulsion Laboratory said it’s as if, “you have two automobile-sized things, one in Los Angeles and one in San Diego, and you’re measuring the distance between them to the size of a red blood cell.”
The entire globe is mapped about once every month, with blue areas on the map showing where the force of gravity is weaker and red spots indicating a stronger force. The fluctuations are not actually caused by changes in gravity, but are the result of differences in the distribution of mass on the Earth’s surface, which can be a result of land areas rebounding from the enormous weight of ice under which they were buried during the last ice age. Other variations can indicate changes in distribution of water following the melting of ice sheets, heavy rainfall, or changes in the amount of moisture in soils. The shifting of such amounts of water create measurable changes in the gravitational field of the planet.
In only five years of operation, GRACE has already obtained dramatic information for researchers to study. In late 2005 GRACE detected the faster-than-expected melting of the Greenland ice sheet, with a resulting rise in sea level of .016 inches per year.
Unlike other satellite systems GRACE has the ability to not only detect changes in surface water, but to monitor water beneath the surface such as groundwater or the amount of moisture contained in the soil, important information for people dependent on such water sources.
Hydrologists are attempting to find ways to use information provided by the GRACE mission to assist farmers. Such information could monitor snowpack in the mountains to predict the amount of moisture available for agriculture, and could also be useful in assessing the risk of spring flooding in areas of the Midwest downstream of large snowpacks.
This entry was posted on Tuesday, September 25th, 2007 at 12:46 pm and is filed under Space Agency News, Technical Concerns. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
