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Atmospheric Sciences & Global Change
Research Highlights

December 2009

Better-than-new LIDAR provides 24/7 atmospheric aerosol data

Raman lidar
Improved data processing from this Raman lidar is helping researchers better determine how aerosols affect cloud formation and climate. The instrument, at the Southern Great Plains site in Oklahoma, sits behind a domed vestibule (front) that protects it from the elements. Enlarge Image

Results: A team of researchers from eight institutions led by Pacific Northwest National Laboratory has solved a software and hardware problem that had perplexed scientists studying atmospheric aerosols for climate research. Not only did they fix the problem, but the instrument now performs better than it did when it was new.

Why it matters: Getting accurate data is the cornerstone of making predictions about how the climate will change as carbon dioxide concentrations continue to rise in the atmosphere. Much of the uncertainty in projections of global climate change is due to the complexity of clouds, aerosols, and cloud-aerosol interactions and to the difficulty of incorporating this information into climate models. Aerosols, tiny particles suspended in the atmosphere, absorb and scatter sunlight, which can contribute to climate change. By calibrating all measurements to consistent standards, the data can help reduce scientific uncertainties in computer models used to simulate climate change.

Methods: A lidar, similar to a radar that calculates distances by bouncing radio waves off of objects, measures how light bounces off aerosols in the sky. An analysis of ground-based Raman lidar data from the Atmospheric Radiation Measurement (ARM) Climate Research Facility's Southern Great Plains site in Oklahoma showed that the lidar's aerosol measurements were off by 50 percent in 2003. Built 10 years earlier, this Raman lidar was designed to take measurements continuously, night and day. To fix the problem, researchers upgraded the electronics and other hardware. By 2005, the refurbished and upgraded Raman lidar was back in business. But when researchers investigated more data in 2006, the data still looked off compared to benchmark data collected by a NASA instrument known as the Ames Airborne Tracking Sunphotometer.

In order to make the data understandable, the researchers turned to the computer program that processed the raw signals. PNNL researcher Dr. Rob Newsom had some ideas about what the problems were with the raw signal processing algorithm. After modifying the algorithm, he noticed a significant improvement in processed water vapor data when compared to water vapor data gathered independently using another atmospheric measuring instrument. The modified algorithm was then applied to the aerosol data, which resulted in a significant improvement in aerosol data products as well. Rather than being off by 50 percent, the Raman lidar was within 8 percent of the airborne sunphotometer standard. Now, improved data processing for the Raman lidar will provide plenty of quality data to help determine how aerosols affect cloud formation and the energy balance from the sun.

Acknowledgments: The Pacific Northwest National Laboratory is transforming the nation's ability to predict climate change and its impacts. The Atmospheric Radiation Measurement (ARM) Climate Research Facility is a scientific user facility funded by the U.S. Department of Energy's Office of Science, Office of Biological and Environmental Research. Additional support came from NASA's Radiation Science and Airborne Science Programs.

Research team: Beat Schmid, Connor J. Flynn, Rob K. Newsom, of Pacific Northwest National Laboratory; David D. Turner of University of Wisconsin-Madison; Richard A. Ferrare and Marian F. Clayton of NASA Langley Research Center; Elisabeth Andrews of University of Colorado at Boulder; John A. Ogren of NOAA/ESRL at Boulder; Roy R. Johnson, Warren J. Gore and Philip B. Russell of NASA Ames Research Center; and Roseanne Dominguez of University of California Santa Cruz.

Reference: B. Schmid, C.J. Flynn, R.K. Newsom, D.D. Turner, R.A. Ferrare, M.F. Clayton, E. Andrews, J.A. Ogren, R.R. Johnson, P.B. Russell, W.J. Gore and R. Dominguez. August 2009. Validation of aerosol extinction and water vapor profiles from routine Atmospheric Radiation Measurement Program Climate Research Facility measurements, J. Geophys. Res., 114, D22207, doi:10.1029/2009JD012682, Nov. 28, 2009.

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