The National Aeronautics and Space Administration (NASA) received an emergency request for imagery from the California Department of Forestry and Fire Protection and has responded by flying its UAV over 4,000 square miles of forest from Santa Barbara north to the Oregon border. The UAV is flown by remote control from take-offs at NASA's Dryden Flight Research Center at Edwards Air Force Base, Calif.

"Firefighters are blinded by the smoke of a fire, but they need to know where the hottest parts of a fire are burning, and any little hot spots that are out in front," said Vincent Ambrosia, NASA Ames Research Center's principal investigator for the fire mission. "Most temperature sensors are calibrated to sense low-temperature sources; for instance, the military wants to use UAVs to sense a person walking across a field at night. But that kind of sensor doesn't work well for high-temperature sources.

"By calibrating our thermal sensors for high temperatures, we can tell whether a given area is actively flaming or just extremely hot ash—a 'boot melter'—because you don't want to send in firefighters if it's going to melt their boots."

Ironically, NASA had already planned an Ikhana demonstration for firefighting missions later this summer. Now, instead of demonstrating its capabilities, the Ikhana is proving its worth fighting real fires. The Federal Aviation Administration (FAA) has given the Ikhana a wide berth, keeping other flights away from the UAV's path to facilitate accurate imaging of burning fires.

The Ikhana aircraft is based on the same airframe as the military's Predator drones, which are manufactured by General Atomics Aeronautical Systems. NASA obtained the Ikhana for use as a test bed for advanced sensor projects. After receiving the emergency request from the California Forestry Department, NASA quickly installed its Autonomous Modular Scanner, which has been calibrated to enable the Ikhana to map fire locations by temperature.

NASA is flying the UAV over active fires in California, then overlaying the most-current hot-spot information on digital maps, which are sent to firefighters in the field in as little as 10 minutes.

"The Autonomous Modular Scanner has 12 spectral ranges that span from visible light through thermal infrared," said Ambrosia. "For the fires we are concentrating on today, its two thermal channels have been highly calibrated to register discrete temperature changes of half a degree [centigrade] all the way to about 1,000°C [1,832°F] without saturation."

All 12 channels collect data simultaneously, using a common lens and a mirror system that scans horizontally. As the aircraft moves forward, the always-on horizontal scanner "paints" images onto separate detectors for each channel.

Besides traditional visible sensors, the Autonomous Modular Scanner uses an advanced mercury-cadmium-tellurite detector for sensing heat in its two thermal channels. Mercury cadmium telluride sensors can be tuned to any desired infrared wavelength by mixing the cadmium tellurite semiconductor with the mercury-tellurite semimetal, to achieve any bandgap between 0 and 1.5 eV.

The Ikhana has enough on-board data storage for 20 hours of scans, but for fire detection it is streaming its data while flying over active fires. To streamline the detection of hot spots further, NASA had crafted an algorithm that runs on the Ikhana using a temperature threshold setting to call out the "hot pixels" that indicate the hottest parts of a fire.

Initially, the flights concentrated on the burning corridor from the Sierra Nevada Mountains west to the Cub Complex and south to the Gap Fire in Santa Barbara County, but now the Ikhana is ranging farther north, to map all fires still burning in California.

The imagery is transmitted simultaneously to the Multi-Agency Coordination Center in Redding, Calif., and the State Operations Center in Sacramento, after which it is transmitted to firefighters in the field.