Friday, March 28, 2008

Wildfire smoke reaches higher and farther

Environmental Research Web: Smoke from wildfires disperses more widely than previously believed, according to a team of US scientists who used space-based stereo imaging, rather than LIDAR (light detection and ranging) observations, to analyse the height reached by smoke plumes. The team found that at least 10% of 650 wildfire smoke plumes in the Alaska-Yukon region during the summer of 2004 reached the free troposphere.

"Computer models are used to predict the climate and health impacts of aerosols, by simulating the way the atmosphere disperses smoke and other particles," Ralph Kahn, who is now at NASA Goddard Space Flight Center after time at the Jet Propulsion Laboratory, California Institute of Technology, told environmentalresearchweb. "Most such models currently assume that wildfire smoke is injected only into the near-surface boundary layer. If smoke is instead injected above the boundary layer, the particles are likely to travel farther, and to remain in the atmosphere longer."

Kahn believes that improving the way smoke is represented in air quality and climate prediction models is particularly important as wildfires are expected to become even more common in some regions as a result of climate change.

He and colleagues at the Jet Propulsion Laboratory at California Institute of Technology, Columbus Technologies and Services, and Harvard University used data from the Multi-angle Imaging SpectroRadiometer (MISR) instrument onboard the Terra satellite. This uses nine cameras with slightly different viewing angles, collecting data in four colour bands – blue, green, red and short-wave infrared.

"Over a period of seven minutes, each of MISR's cameras successively images the same location along a roughly 400 km wide strip nearly from pole to pole, so we end up with nine multi-angle views of the entire swath," explained Kahn. "MISR images the entire planet about once per week, at spatial sampling as high as a quarter of a kilometre."

MISR observations provide information about everything on Earth that scatters light differently at different angles – the surface, clouds, and particles of dust, smoke and pollution suspended in the atmosphere. "The multi-angle data tell about the amount, size, shape, and brightness of aerosols," said Kahn. “And from the hyper-stereo of the multiple views, we can derive the heights of clouds and smoke plumes."

Space-based LIDAR has to date found smoke only near the surface in the vicinity of wildfires. "LIDAR can measure the heights of aerosol layers much thinner than those for which the multi-angle stereo technique works," said Kahn. "But multi-angle imaging provides vastly greater spatial coverage, and in particular, often observes active wildfires missed by the extremely narrow lidar swath."

…The researchers reported their work in Geophysical Research Letters.

Smoke from this August 2006 wildfire at the Devils Backbone, Crater Lake National Park, Oregon, USA, may have reached into the troposphere. Photo by Wing-Chi Poon, Wikimedia Commons

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