The U.S. National Oceanic and Atmospheric Administration (NOAA) over the next three weeks will test a remotely piloted aircraft as a possible first step toward using unmanned drones to deliver detailed weather forecasting information and to monitor protected areas for illegal fishing, agency officials said.

NOAA managers and scientists are quick to point out that they have no intention of replacing weather satellites with unmanned aerial vehicles (UAVs) like the General Atomics Altair aircraft, which was scheduled to begin its test campaign over the Pacific Ocean off Los Angeles April 29 . Aircraft cannot match the global coverage of satellites, they said.

The planes would be dispatched to focus on specific weather or oceanographic phenomena such as rain bands of hurricanes, algae blooms or the so-called Pineapple Express tropical air currents that produce heavy rain and snow along the West Coast of the United States most winters.

UAVs also could be equipped with cameras to monitor marine sanctuaries and track sea mammals. “I think the consensus is, it’s not a matter of if but when these platforms will be available [to NOAA] for operational uses,” said Mike Aslaksen, project manager for the six-flight NOAA UAV demonstration. “We’re going to look at how they fit into our operational needs,” he said.

Aircraft can get closer to targets of interest than satellites, and thus often can produce finer images of cloud formations and other features. Unmanned aircraft have the added advantage of being able to stay aloft for 20 hours or longer, said Al Gasiewski, co-project scientist for the Altair UAV and a scientist at NOAA’s Environmental Technology Laboratory in Boulder, Colo.

For instance, he said, a moisture-sensitive microwave instrument on a UAV should enable scientists to observe the entire evolution of individual thunderstorm cells inside hurricane rain bands. Comparable satellite instruments such as the Advanced Microwave Sounding Units on NOAA’s Polar-orbiting Operational Environmental Satellites show a “somewhat blurry collection of cells,” Gasiewski said.

Engineers at General Atomics Aeronautical Systems Inc. built the Altair UAV in Adelanto, Calif., as a scientific variant of the U.S. military’s Predator B Hunter-Killer aircraft that carries both spy sensors and bombs. Predator B is a larger and higher-flying version of the original Predator flown in Iraq and Afghanistan. NASA helped fund development of Altair, which flew for the first time in June 2003.

According to General Atomics, Altair can fly to 15,600 meters high and stay aloft for 32 hours. In NOAA’s demonstration, Altair will fly as high as 13,500 meters and for as long as 20 hours, said Aslaksen. A controller in a General Atomics command center in Gray Butte, Calif., will guide the plane to an altitude of approximately 5,400 meters over the Edwards Air Force Base, Calif., flight range, and then steer it toward the Pacific Ocean using a route over sparsely populated areas of California, Aslaksen said.

SES Americom’s AMC 5 satellite will provide Ku-band links between the aircraft and the command center.

The plane is conducting the demonstrations over the Channel Islands National Marine Sanctuary off Long Beach, Calif., and farther west over the Pacific Ocean. NOAA scientists have equipped Altair with five instruments:

A Combined Ozone Photometer and Gas Chromatograph to measure 12 gases thought to be linked to global warming, ozone depletion and pollution;

An Ocean Color and Passive Microwave Vertical Sounder to deliver ocean-chlorophyll images and atmospheric-moisture readings;

A spy camera called the Electro Optical/Infrared Gyro Stabilized Imaging Sensor to watch fishing boats in or around marine sanctuaries and to identify marine mammals for migration research;

A Direct Geo-referenced Digital Camera for shoreline mapping in remote areas;

And finally, a lightweight computer called the Research Environment for Vehicle-Embedded Analysis on Linux , which will use Iridium satellite links to test telepresence technologies that someday could enable far-flung researchers to monitor and control UAV experiments in near-real time . In one experiment, scientists will compare the ocean color images from Altair to those taken by the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) on the OrbView 2 satellite to see if they can overcome a shortcoming of the space-based sensor .

“When you get near a coastal zone, the spatial resolution of SeaWiFS often is not good enough to discriminate between land and water. The boundary is blurred,” Gasiewski said. SeaWiFS’ resolution, which refers to the size of features it can discern, can be as fine as 1.1 kilometers, according to the official mission characteristics posted by NASA. The Altair ocean color sensor’s resolution can be as fine as half a kilometer depending on the altitude, Gasiewski said.

The plane’s microwave instrument will study the Pineapple Express air currents also known to scientists as atmospheric rivers. These typically extend from the ocean surface to an altitude of a few kilometers.

“The NOAA [Geostationary Operational Environmental Satellite] sensors can’t see the moisture very well because they can’t see through the clouds,” Gasiewski said. The microwave sounding instrument on NOAA’s polar-orbiting satellites can detect the rivers, but its 25-kilometer resolution is not fine enough to capture the structural details of the rivers, which can be as narrow as a few kilometers across, he said.

Altair’s microwave sensor offers half-kilometer resolution, Gasiewski said. NOAA had hoped to begin the Altair flights in mid-March, but Aslaksen said it took longer than expected to win approval for the flights from the Federal Aviation Administration and NASA, which is working with San Diego-based General Atomics to ensure the plane flies safely in public air space.

“The schedule slip is attributable to the new ground we’re breaking here, and that’s safely integrating UAVs into the National Air Space System,” Aslaksen said.