EDWARDS AIR FORCE BASE, Calif. - There will be a powerful new scientific eye in the sky come summer.

NASA and Northrop Grumman have unveiled two unmanned drones that will be used for atmospheric research.

One of the two Global Hawks, a version of the U.S. air force's top-of-the-line unmanned spy plane, will be outfitted with science instruments this spring and conduct its first earth science mission in June for NASA.

The planes, which are capable of staying aloft for more than 30 hours, will sample greenhouse gases responsible for ozone depletion and verify measurements by NASA's Aura atmosphere research satellite.

Previous research aircraft deployed to sample the atmosphere typically are smaller and cannot stay airborne for as long as the Global Hawk can.

During the Global Hawk flights, scientists will have access to their instruments through a dedicated satellite feed and can view data in real time.

"It's a whole new ballgame for us," said project scientist Paul A. Newman of NASA's Goddard Space Flight Center.

NASA received two Global Hawks from the air force in 2007. The computer-controlled, high-altitude drone has been used for surveillance in Iraq and Afghanistan and to monitor wildfires in the United States.

Global Hawk maker Northrop Grumman Corp. last year received a five-year contract of up to $25 million to support NASA's Global Hawk program.

With a wingspan of 35 metres, the Global Hawks can fly up to about 20,000 metres, which is twice the altitude of commercial airliners. The craft can also carry payloads up to 900 kilograms.

Missions will fly in and out of Edwards Air Force Base north of Los Angeles. Initial flights will last several hours and eventually ramp up to 30 hours with targets over the Pacific and Arctic.