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Fire is a force of nature that humans have harnessed to make
our lives easier and more productive — by heating our
homes, cooking our food, and clearing away obstacles. But
though we employ it regularly to our benefit, fire can very
easily become a destructive force — through our carelessness
and mistakes or via more spontaneous, natural means. Candles
left alone can ignite the curtains, backyard brush fires can
quickly grow out of control, lightning can ignite forest fires,
and hot ash and magma from volcanic eruptions can ignite almost
anything they touch.
In addition to the immediate dangers fires present, they
also release damaging gases and airborne particles into the
atmosphere. These emissions affect ecosystems and atmospheric
chemistry near the site of the fire, and can also be transported
long distances. For instance, the springtime agricultural
fires in Southeast Asia create smoke and gases that get blown
across China and far out over the Pacific Ocean. Because fires
have such a profound role in the global climate and in peopleÆs
everyday lives, and because they are so widespread across
the Earth, scientists have turned to satellites for regular
observation of global fire patterns. MODIS fire scientists
have developed an important new data product called Thermal
Anomalies, Fires, and Biomass Burning to take advantage of
the fire-detection capabilities of the MODIS sensors on the
Aqua and Terra satellites.
MODIS can see fires because fires have a recognizable thermal
signature. Whenever the product detects a "hot spot," it flags
the signal's location in the data set. When the data get turned
into an image, the fire-detection locations from the product
are added as an overlay on the image, which marks the fires
in bright red. Via the MODIS
Rapid Response System, this product made it possible to
track large fires such as the Biscuit Complex fire in Oregon
and California during July 2002, and the large bushfires in
southeastern Australia that burned over two million acres
during the first two months of 2003.
Under near-ideal conditions - nadir (straight-down) look
with no clouds in the way, not too much smoke, relatively
cool background terrain for comparison, etc. - the product
can detect fires as small as 50m2. For instance, a small,
very hot fire in a cold area, such as an oil-well fire during
the winter, would be detectable under the above criteria.
But considering that about 70 percent of the planetÆs surface
is covered in clouds at any given time, these ideal circumstances
are hard to come by. MODIS can routinely detect fires at an
average size of 30 meters by 30 meters (900m2) under a variety
of conditions: differing satellite positions, all MODIS scan
angles, and both relatively hot and cool fires. Under these
more typical circumstances, the algorithm can detect a fire
about the size of a quarter acre — about a third of
the size of an American football playing field. This is quite
a feat, considering that at MODISÆ highest resolution, one
pixel covers 250 square meters. At this resolution and under
the above-stated near-ideal circumstances, MODIS will detect
a fire covering only four pixels almost 100% of the time.
A MODIS instrument flies in an orbit 705 kilometers above
the Earth Ô thatÆs the about of the distance between Cancun,
Mexico, and the Florida Keys, USA Ô and receives data from
the entire surface of the Earth every two days. MODIS completes
one orbit around the earth every 98 minutes, which makes it
well suited for gathering data about time-sensitive events
like fires. Add to that the fact that there are two MODIS
instruments in orbit, and the differences in fires between
morning and afternoon can be detected. This frequent coverage
is especially important during fire seasons, when huge wildfires
can start in the blink of an eye. Having morning and afternoon
looks at the same area also allows scientists to monitor changes
in fire frequency, intensity or location over the course of
the day.
At institutions like the US Forest Service (USFS), the National
Interagency Fire Center (NIFC), and the U.N. Global Fire Monitoring
Center, the MODIS Fire Product is routinely used for imagery
and maps that aid fire managers in monitoring fires across
a large area and allocating resources to regions where they
are needed most. These institutions are able to receive MODIS
fire data quickly because of the MODIS
Rapid Response System, which was designed to automate
the computer processing of the fire detection data product
and deliver the results to partners in near real time (within
2-4 hours of when MODIS collected the observations). Because
of the dynamic nature of fires, and because uncontrolled fires
can be very costly, having up-to-date and accurate fire information
is very important. In addition to providing this product to
various agencies via Rapid Response, results of the product
are visible to the general public in much of the MODIS imagery
available on this site, in the Visible
Earth database, in the Rapid Response gallery,
and in the Natural
Hazards fire section of the Earth
Observatory.
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