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'First-look' results with spectro-radiometer: All systems 'Go'

James E. Kloeppel, Physical Sciences Editor
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SAN FRANCISCO -- Demonstrations of the unique, three-dimensional, cloud-imaging capabilities of the Multi-angle Imaging Spectro-Radiometer -- one of the instruments on the satellite Terra -- will be among highlights presented at a special session devoted to the satellite at the American Geophysical Union Fall Meeting on Tuesday morning, Dec. 19.

Lofted into orbit on Dec. 18, 1999, Terra is the flagship of NASA's Earth Observing System Program, an international effort to monitor Earth's climate during the next 15 years. The satellite's five instruments will help scientists understand how clouds, aerosols, air pollutants, oceans, vegetation and ice cover interact and impact the climate.

"Our 'first-look' results with MISR are very encouraging," said Larry Di Girolamo, a professor of atmospheric sciences at the University of Illinois. "MISR is the first instrument to make global, high-resolution, multi-angle, multi-spectral radiometric measurements of Earth from space. The instrument can characterize cloud, aerosol and surface properties in a manner no other satellite has been capable of."

Unlike traditional meteorological satellites that have only one camera, MISR has nine cameras that successively view portions of the planet in four spectral bands.

"By combining spectral and angular signatures, we can gather much more information about atmospheric or surface features," Di Girolamo said."The use of multiple cameras also permits stereoscopic imaging, allowing us to look at clouds in 3-D."

By fusing the views from different cameras, researchers can also pick out the wind field at different cloud elevations. "For example, we can observe the rotation of a hurricane at various altitudes in 3-D," Di Girolamo said. "This has never before been done with a polar-orbiting instrument."

MISR's geometrical measurement technique also permits reliable detection of clouds over terrain that is typically very difficult to observe -- such as desert sand and arctic snow mass. In such environments, traditional single-view techniques are often unable to differentiate cloud cover from surface features.

The accurate measurement of polar cloud cover is particularly important to climatologists in modeling global warming. "Since Terra was launched, we've been checking out the instruments and verifying that the data-processing algorithms are working correctly," Di Girolamo said.

The algorithms convert the raw data into meaningful geophysical products - such as cloud cover, surface reflectance, cloud albedo and cloud height.

"Currently, we can't keep up with the tremendous amount of data coming in, so some of the higher-level products are not being generated for all of the data," Di Girolamo said. "No information is being lost - it's all being stored for a time when we have bigger, faster computers. Then we will go back and process all of the data."

The MISR cloud-imaging project is a collaboration between researchers at the UI, Jet Propulsion Laboratory, University of Arizona and University College London.