Smoke Sentry in Space
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You can be sure that more than one weary firefighter has looked toward the heavens in recent days hoping for relief. Most, perhaps, are thinking of rain or maybe a cool breeze.
NASA can't render that kind of aid -- at least not yet -- but there is something up there that can help: a new orbiting sensor that can spot the heat from fires and help firefighters plan their attack against the inferno.
Above: Wildfires are clearly visible from the lofty perch of Earth orbit. In addition to the smoke plumes, the satellite-based sensor being used for this project can "see" the infrared heat emitted by the flames themselves -- denoted in this August 18 image of Washington State as red outlines. [click on image to] Image courtesy of NASA's MODIS project.
The sensor, called MODIS (short for the Moderate Resolution Imaging Spectroradiometer), rides aboard NASA's Terra satellite and "sees" infrared heat emitted by fires on the planet below. MODIS data can be quickly transformed into "Active Fire Maps" that show where wilderness fires are raging and where they're heading -- data that fire response planners covet.
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"The maps can also help the public understand where the fires are located," Forbes added. Anyone can look at the most current maps produced by the project by pointing a Web browser to the website for the USDA Forest Service's Remote Sensing Application Center.
NASA, NOAA, the University of Maryland, and the Forest Service are working together to deliver these Active Fire Maps where they're needed most -- in the hands of firefighters. The collaborative program, called the Rapid Response System, is well underway. Firefighters using the Internet can now access Rapid Response data within hours of a Terra overpass. By October, 2001, when the Forest Service completes a new satellite downlink facility in Utah, the delay will be as brief as mere minutes.
Below: This August 19th Active Fire Map shows roughly the same area as the visible-light image above. Yellow indicates previously burned areas, while red denotes active fires. (Note that text is also in red.) Click on the image for a. Images courtesy of the Forest Service [ more information].
last year -- which was the worst since 1910 -- and the need for up-to-date information."
Says Wei Min Hao, a senior scientist with the Forest Service who also helped organize the project: "Satellite data can play a very big role, especially if there's heavy smoke and [we're] not able to send a reconnaissance plane to map fires because of the low visibility."
The Terra satellite, which carries MODIS, circles the Earth from pole to pole in an orbit that allows the sensor to image most of our planet's surface every day. The polar orbit keeps Terra in a constant alignment with the Sun, so it passes overhead at the same local time each day -- about 10:30 a.m.
There's no need to worry about privacy, though. Each pixel in a MODIS image covers 250-1000 meters on the ground (depending on the frequency of light considered), so only very large features are visible. This resolution is adequate for providing rough maps of large fires -- a square pixel 1000 meters long covers about 250 acres, and forest fires often burn tens of thousands of acres at a time.
Because of MODIS's coarse resolution, Active Fire Maps will be used to formulate broad strategies, not to make detailed decisions about on-the-spot tactics. Tactical decisions require more detailed aerial photographs or imagery from satellites like Landsat, which has pixels that are 15-30 meters in size.
"For example, we might have fires in wilderness areas that we would want to monitor, but we really don't need to spend a lot of time and money having aircraft map those sites as precisely as we would a fire that's near an urban area," says Tom Bobbe, a center manager with the Forest Service.
When MODIS looks down on Earth it senses both visible light -- light that the human eye can see -- and thermal infrared (IR) radiation emitted by hot objects. In other words, it can detect both the smoke and the fire. Furthermore, MODIS senses not just whether the ground is hot, but how hot.
"We are developing a unique capability to show the intensity of the fire. We can measure something about its heat level even through intervening smoke, to a reasonable degree," says Vince Salomonson, the MODIS science team leader at the Goddard Space Flight Center.
And when those hot fires are finally extinguished, MODIS still comes in handy!
To the human eye, thriving forests appear green while the charred areas after a fire look black. But MODIS sees much more than simply "green" or "black." MODIS is a spectrometer -- it senses many colors spanning the visible and IR portions of the electromagnetic spectrum. When light --meaning visible light or IR radiation-- bounces off trees or other objects, the molecules at the objects' surfaces leave their "fingerprints" imprinted in the reflected spectrum.
By looking at such spectra, forest managers can track the recovery of an area after a fire, because the spectral fingerprint of an area evolves as first weeds and grasses, then small trees, then large trees repopulate the land.
Below: If your eyes could see infrared light, the world might look more like the bottom image of this pair. The white areas represent warm objects emitting IR radiation. Notice that the roof of the house, the transformer on the telephone pole, and the rock outcrops on the mountains in the distance all shine brightly with IR light, while the sky -- bright in visible light -- appears dark.
In the future, MODIS maps and other Terra-derived data will help teams of scientists rehabilitate burned areas. They will use burn severity maps -- derived from satellite and ground measurements -- to prevent further erosion, soil loss and adverse impacts to water quality. The maps will also help scientists identify critical wildlife habitat affected by the fire and facilitate reforesting an area.
Says Ghassem Asrar, NASA's Associate Administrator for the Office of Earth Science, "our investment in the Terra Earth Observing System is starting to pay tremendous dividends to the American taxpayer." And to firefighters! Battling wildfires remains a dangerous job, best done on the sweltering ground. But with MODIS lending aid from the cool of space, firefighters are gaining an extra edge on their ancient and fiery adversary.
Notes: Rob Sohlberg at the University of Maryland's Department of Geography and Jacques Descloitres at NASA's Goddard Space Flight Center lead the Rapid Response Project. The Terra spacecraft is part of NASA's Earth Science Enterprise, a long-term research effort being conducted to determine how human-induced and natural changes affect our global environment.Web Links
NASA Satellite, University Of Maryland and U.S. Forest Service Provide Rapid Response to Wildfires -- a joint NASA, Forest Service, and University of Maryland press release.
MODIS home page -- information on the satellite-based instrument that will be used for the firefighting system, from NASA's Goddard Space Flight Center
Remote Sensing Application Center -- daily Active Fire Maps, from the U.S. Forest Service
National Interagency Fire Center -- links to other fire maps
Right: The MODIS instrument aboard NASA's Terra satellite. [click on image to enlarge] Image courtesy Terra Project.
Terra -- home page for the Terra Project
USDA Forest Service -- home page
Forest Service daily fire report -- overview of the wildfire situation in the U.S., updated during the firson
NASA's Visible Earth -- for examples of MODIS images, enter "MODIS" in the search field
Watching Wildfires from Space -- Science@NASA article: NASA's Earth Probe satellite is keeping an eye on smoke from wildfires raging across the Western US.
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