The U.S. space agency NASA has launched what it calls a major mission in understanding Earth's weather and longer term climate. It has boosted the Aqua satellite into orbit from Vandenberg Air Force Base in California to study our planet's water cycle for the next six years.

Data for better weather predictions will soon come from the heavens specifically at an altitude of 700 kilometers from a new U.S. satellite named Aqua, the Latin word for water.

"The prime goal of the Aqua mission is to help understand the water cycle and use that to improve weather forecasts on the short-term and ultimately also seasonal forecasts," says George Aumann, an Aqua mission scientist at NASA's Jet Propulsion Laboratory in Pasadena, California. Mr. Aumann explains that the satellite will measure ocean circulation and evaporation, sea and land ice, snow cover, clouds and water vapor in the atmosphere, precipitation, and global temperatures.

For example, Aqua will examine 2,400 points in a vertical slice of the atmosphere, about 100 times more than most satellites can observe.

Some of its instruments will measure heat, which emits infrared radiation below visible light wavelengths. As a result, researchers can take measurements 24 hours around the clock instead of relying on daylight.

Mr. Aumann says making more accurate daily and seasonal weather forecasts from this information will be a great economic benefit, especially to farmers. "From an agricultural viewpoint, there are two things. You don't want to be surprised, for example, by a sudden frost or a sudden rainstorm so the farmers can take preventive actions," he says. "The second one is longer range. If you can predict weather on a seasonal basis, that would allow the farmers to plant appropriate crops to maximize yield or perhaps to harvest early if the weather is predicted to turn bad."

In addition to gathering water cycle data, the Aqua satellite will also measure plant cover on land and tiny floating sea vegetation called phytoplankton. Scientists hope this will help them understand changes in biological systems that depend on water.

Aqua is a companion satellite to one named Terra launched in December, 1999. Terra crosses the equator in the morning and Aqua will pass over in the afternoon. Together, they will show scientists how the key measurements they gather vary during the day.

Both are joint projects of the United States, Brazil, and Japan, each of which provided instruments.