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Airborne Multispectral Radiometer Images Fire and Ice

Photonics Spectra
Oct 1998
Daniel C. McCarthy

It is difficult enough to prevent and detect wildfires, but even after one has been spotted, its potency and path are unpredictable. Now a device that could map these erratic fires is being developed, based on the two most common technologies that have been used for this purpose.

Snow-capped Telegraph Peak, near Los Angeles, appears yellow-green in the background of the infrared image. From the same distance, though enlarged, Space Instruments' radiometric thermal imager reveals temperature differences of 0.8 °C in the snow and ice.

The Forestry Service arm of the US Department of Agriculture relies on infrared line-scan imagers borne by large aircraft, but these devices are expensive, heavy and unwieldy. Microbolometer technology has created other options for uncooled spectral imagers operating in the infrared that are lighter in weight and adaptable enough to detect hot spots through smoke or darkness. These instruments, however, lack the sensitivity required for remote airborne sensing operations.

The best of both technologies

Innovative early prototypes of a multispectral thermal imager that combine the best of both technologies have won Space Instruments Inc. a contract to build an airborne model for evaluation by the Forestry Service. The company hopes to have a model ready for flight within a year, according to James Hoffman, technical director.

The system, called FireMapper, is a four-band radiometer that provides thermal imaging using a microbolometer detector array. Instead of relying on bulky motors to perform scans, however, the system uses the movement of the aircraft over the landscape to scan in push-broom fashion. According to Hoffman, the push-broom mode also makes better use of the device's 245 rows of detectors, allowing them to integrate information contiguously row by row. A digital processor delivers the data in real time.

"This gives us enough dynamic range to use the system to measure either the energy of wildfires or the canopy temperature of a forest to assess how quickly the trees are using up water," said Phil Riggans, fire scientist for the Forestry Service based in Riverside, Calif.

Hoffman pointed out that the system also delivers spectral images of snow- and ice-covered areas, with detail down to differences in temperature that are less than a degree apart.

According to Riggans, Brazil's forestry service, IBAMA, also has expressed interest in the system to detect trails made by illegal logging in the Amazon basin. "One of their biggest problems is timely information when illegal cutting is taking place," he said. "During the dry season in Brazil there's an extensive smoke pall over the lower Amazon, but Space Instruments' FireMapper can see through that layer and spot loggers' skid trails."


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