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Animation of all 50 MAS bands, from .547
µm to 14.17 µm. (2.4MB)
False color flyover of Brazilian fires using MODIS
Airborne Simulator (MAS) data. The bands used simulate what would be seen in
visible light. (3.3MB)
Flyover from the same flight track, using infra-red bands. The heat of
the fires shows up bright red. (1.2MB)
Combined visible-like and IR bands. Note the fires that
can be seen underneath the smoke. (1.2MB)
(All images & animations by Robert Simmon, with the gracious help of Pat Hrubiak, Goddard DAAC) |
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NASA Demonstrates New Technology for Monitoring Fires from Space
by David Herring
May 29, 1998
Earth
scientists at NASA's Goddard Space Flight Center recently demonstrated that the
MODIS instrument, scheduled to launch in December 1999 on NASA's Earth Observing System Terra satellite, will have unprecedented abilities to detect forest fires
anywhere on the surface of our planet. In two recent scientific papers, the
scientists announce that MODIS (or Moderate-resolution Imaging
Spectroradiometer) will measure the intensities of fires and will therefore
enable them to detect active fires, accurately estimate rates of combustion, as
well as the amounts of emission productssuch as smoke, greenhouse gases, and
aerosol particlesthe fires produce.
Coincident images of the Brazilian rain forest, at
.657 µm (red) and 4.05 µm (thermal infra-red), respectively. The
visible light image shows only smoke, while the thermal infra-red image shows
details of the fire beneath it. These data were acquired by the MODIS Airborne
Simulator on August 23, 1995.
According to the papers' principal authors, Drs. Yoram Kaufman, of NASA's
Goddard Space Flight Center, and Chris Justice, University of Virginia, the new fire monitoring capability
MODIS provides could greatly enhance our abilities to more efficiently manage
natural resources and more effectively combat wild fires. Moreover, in concert
with other space-based sensors, MODIS will enable scientists to assess the
impacts fires may have on air quality near local communities, or even
metropolitan areas.
Kaufman, Terra project scientist, explains that due
to MODIS' moderate (1-km) resolution, most fires will be too small to be seen by the sensor. Consequently, it will only detect about 25
percent of the fires burning worldwide. Yet, because those are the larger, more
intense fires, they are responsible for 80 to 100 percent of the biomass burned.
"This is an important point, because until recently, scientists didn't fully understand the relationships between the radiative energy a fire emits, its rate of combustion, and the resulting emission products," Kaufman states. Based upon
the results from the 1995 "Smoke, Clouds and Radiation" (SCAR)
campaign in Brazil, the authors conclude that "a fire's radiative energy output
is highly correlated (97 percent) with the generation of the burn scar and
therefore with the consumption of biomass." (SCAR was sponsored jointly by NASA and the government of Brazil.)
Fires generally burn at
temperatures anywhere from 500K to 1400K (440�F to 2060�F). Fires toward the
higher end of this range become so hot they actually burn down into the soil, in
addition to consuming plants, leeching the soil of its essential nutrients for
sustaining life. Because MODIS is more sensitive to fires' temperatures than
previous satellite remote sensors, scientists can better assess the damage they
cause, as well as help fire fighters prioritize which fires are in most urgent
need of fighting.
"For individual wild fires," Kaufman continues, "the rate
of combustion is an indicator of the strength and danger of a fire, and can be
useful to firefighters in decisions on whether or not to fight the fire, as well
as in developing a strategy for fire containment and suppression."
Scientists will try to use the MODIS data to determine the phase of a given
fire-whether it is flaming or smoldering (flaming combustion is the least
polluting). Although the rate of combustion is higher during the flaming phase,
more smoke, aerosol particles and greenhouse gases are emitted during the
smoldering phase due to the lower combustion efficiency, which has the greatest
influence on regional pollution and, potentially, on global climate change.
Every year, the public media focuses on a number of unusually large
fires burning in various parts of the world. In October 1997, smoke from the
widespread burning in Indonesia covered a large portion of the Asia-Pacific
region and was linked to a high number of health problems and some deaths in
that country. From May through July 1998, more than 1,000 fires have burned in
Southern Mexico and Central America, producing a cloud of smoke so dense and
widespread that visibility in parts of southern Texas was reduced to 2 km. Some
flights in that region were cancelled due to poor visibility and 53 counties
were placed on a health advisory.
"Most people are unaware how extensive
fire is on our planet," observes Justice, lead scientist for the MODIS Land
Discipline Group. "With increasing variability in weather events and climate,
we're likely to see changes in fire frequency and extent and the associated
disturbance to natural and managed ecosystems. For example, we have seen
considerable interannual variability in fire occurrence in Brazil, Africa and
the United States over the last few years. The occurrence of large fires near
populated areas in California in recent years has caused considerable concern
for state and local authorities and highlighted the need for improved fire
management and monitoring."
Co-author Darold Ward, of the U.S. Forestry
Service, states that an estimated 6 petagrams (about 6.3 billion tons) of
biomass are burned worldwide each year. He notes that about 80 percent of all
biomass burning takes place in tropical countries. About 3 to 5 percent of the
worldwide totalor 7 million acresis burned annually here in the United States.
"Approximately 2 to 5 million acres are burned by wild fires in the U.S.
each year," Ward states, "while 5 million acres are burned as 'prescribed'
fires, or fires that are beneficial in managing the ecosystems. Prescribed fires
are deliberately planned and set by fire management officers for a variety of
reasons."
Forest managers often set prescribed fires to prepare a particular
site for tree planting, as well as to kill undergrowth to reduce the competition
from unwanted vegetation. Prescribed fires are used extensively for wildlife
habitat improvements. Prescribed fires are also set and managed to reduce the
potential hazard of larger, uncontrolled wild fire outbreaks. These fires reduce
dead vegetation, or consume "fuel," that has accumulated on the forest floor.
"In the western United States, forests have been well-protected from fire
for the last 60-70 years," Ward explains. "These ecosystems that evolved in the
presence of occasional 'natural' wild fires are now developing 'unnaturally' in
competition with off-site species. Consequently, the forests have become
unhealthy because of the large amount of dead and dying vegetation. This may
lead to the spread of insects, disease, and to disastrous wildfires.
"So, we
recognize that fires are an important part of the ecosystem and we're trying to
bring them back into the ecosystem in a responsible way," Ward concludes. "This
requires fairly aggressive prescribed burning by land managers. We think MODIS
data will be useful in helping us monitor their smoke output in light of air
quality regulations. Additionally, through remote sensing, we can do a better
job of assessing the impacts of fires in restoring the fire-dependent
ecosystems."
MODIS' advanced fire monitoring capabilities were first tested
during the Smoke, Clouds and Radiation (SCAR) campaign held in Brazil in 1995.
Jointly sponsored by NASA and the Brazilian government, SCAR was conducted by a
team of government and university scientists from both nations. During the
campaign, a MODIS Airborne Simulator was flown aboard NASA's ER-2 aircraft (a
U-2 airplane modified for science use) at altitudes of up to 40,000 feet. The
purpose of this simulator is to enable scientists to gather "MODIS-like" data so
that they may refine their data processing techniques in anticipation of the
launch of the real MODIS.
According to Elaine Prins, co-author and research
scientist with NOAA/NESDIS Office of Research and Applications, MODIS is an
improvement upon previous satellite sensors due to its higher "saturation
thresholds" as well as its larger number of spectal channels to better
characterize the atmosphere and fires. By analogy, the sun is so bright that it
quickly "saturates" a human eye when looked at directly. Similarly, remote
sensors can become saturated when viewing hot, bright fires, rendering it
impossible for them to distinguish important characteristics about that fire,
such as its rate of combustion.
"The primary fire detection channel on the
AVHRR (Advanced Very High Resolution Radiometer) has a saturation threshold of
approximately 320K," Prins states. "MODIS has four channels that are sensitive
to fires. Two are located in the infrared portion of the electromagnetic
spectrum at 4 and 11 microns with thresholds at 500K and 400K, respectively, and
can be used to monitor fires day and night. The other two are located at 1.6 and
2.1 microns for nighttime fire detection."
Once certain of its viewing
pixels pass the "brightness temperature" test that identifies them as potential
fires, the data are then run through a computer process to differentiate them
from background pixels that are obviously not fire. Then, the 4-micron channel
data are compared with data from MODIS' 11-micron channel to provide an
additional perspective.
The 4- and 11-micron channels were chosen because
they are "window" channels that enable remote sensors to "see" more clearly
through the atmosphere than most other channels. At night, MODIS can use its
1.6- and 2.1-micron channels for detecting fires, when data in these channels is
acquired. NASA is planning two field campaigns in 1999 to test the accuracy of
the MODIS fire product for Brazil and Southern Africa, two major fire regions of
the World.
According to the authors, MODIS data will also be applied in
other useful and relevant ways. For instance, a fire potential product is being
developed to indicate what regions are susceptible to wild fire outbreaks.
Another co-author plans to use MODIS data to monitor volcanoes and, based upon
sudden temperature increases, help forecast when a given volcano is about to
erupt.
References
Kaufman, Yoram J., Chris Justice, Luke Flynn, Jackie Kendall, Elaine Prins, Darold E. Ward, Paul Menzel, and Alberto Setzer, 1998: "Potential global fire monitoring from EOS-MODIS." Journal of Geophysical Research, 103, pp. 32,215-38.
Kaufman, Yoram J., Richard G. Kleidmann, & Michael D. King, 1999: "SCAR-B fires in the tropics:
Properties and remote sensing from EOS-MODIS." Journal of Geophysical Research, SCAR-B Special
Issue, 103, pp. 31,955-68.
The data used in this study are available in one or more of NASA's Earth Science Data Centers.
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