EOS Validation Program

Institution: NASA/Langley Research Center
                    Chemistry and Dynamics Branch
                    Mail Stop 401A
                    Hampton, Virginia 23681-0001
Phone: (757) 864-9443
FAX: (757) 864-7790
E-mail: r.ferrare@larc.nasa.gov

S. H. Melfi, University of Maryland Baltimore County
Geary Schwemmer, NASA/Goddard Space Flight Center
David Whiteman, NASA/Goddard Space Flight Center
Keith Evans, University of Maryland Baltimore County
David Turner, Pacific Northwest National Laboratory

June 2001
Final Report, February 2003

We propose to use the aerosol extinction and backscattering profiles measured by two separate Raman lidar systems to validate the aerosol climatology models used by two EOS AM sensors, MODIS and MISR. The aerosol retrieval algorithms used by these EOS sensors operate by comparing measured radiances with tabulated radiances which have been computed for specific aerosol models. These aerosol models are based almost entirely on surface and/or column averaged measurements and so may not accurately represent the ambient aerosol properties. Therefore, to validate these EOS algorithms, we propose to develop and use of the aerosol backscattering and extinction profiles measured by the CART Raman Lidar to determine how the aerosol properties over the SGP EOS Validation site vary with altitude and time. Additional activities would focus on the use of the aerosol profiles measured by the GSFC Scanning Raman Lidar (SRL) during periodic field experiments to perform similar assessments.

We propose to use the aerosol and water vapor measurements acquired by both systems for directly validating these EOS instruments. Ground-based measurements of the vertical profiles of atmospheric water vapor and aerosols are required both for direct validation of these instruments as well as to understand the physical processes which affect the retrieval of aerosols and water vapor from these satellite platforms. Both Raman lidar systems directly measure profiles of water vapor mixing ratio, aerosol backscattering and extinction and can, therefore, also provide measurements of precipitable water vapor and aerosol optical thickness. We shall use the SRL aerosol data acquired during the TARFOX experiment at Wallops Island in July 1996 to assess the contribution made by different aerosol layers to the column integrated aerosol properties derived from the ground based sun/sky photometer measurements. We shall also use water vapor and aerosol measurements acquired by both lidars for similar studies during future experiments. Using the data from both lidar systems is a great asset for two reasons: 1) because it is a mobile instrument, the SRL will be able measure different types of aerosols at different locations, and 2) because it is designed for continuous, unattended operations, the SGP CART Raman lidar can acquire long term data sets required for validating EOS measurements over a long period of time.

Additional Information: Vertical profiles of both atmospheric water vapor and aerosols are required for evaluating EOS measurements, and perhaps more importantly, for understanding the physical and chemical processes which affect these retrievals of aerosols and water vapor from these satellite profiles. These measurements are needed to assess the effects of the vertical variability of aerosol optical and physical characteristics on the EOS MODIS and MISR retrieval algorithms. We propose to use profiles of aerosols and water vapor acquired by two separate Raman lidar systems to both evaluate these EOS measurements and to understand the processes which affect the retrievals from these EOS instruments. The Atmospheric Radiation Measurement (ARM) (http://www.arm.gov/) Southern Great Plains (SGP) Cloud and Radiation Testbed (CART) Raman Lidar (http://www.arm.gov/docs/instruments/static/rl.html) and the NASA/Goddard Space Flight Center (GSFC) Scanning Raman Lidar SRL (http://rsd.gsfc.nasa.gov/912/Raman/raman.htm) both directly measure profiles of both aerosol backscattering and extinction and can, therefore, provide measurements of aerosol optical thickness to directly validate the EOS measurements. We shall apply the procedures developed for analyses of data acquired by the SRL to analyze the aerosol extinction and backscattering profiles measured by the SGP CART Raman Lidar. Because it is designed for continuous, unattended operations, the SGP CART Raman Lidar is well suited to provide the long term data sets required for validating the EOS MODIS and MISR measurements. Automated algorithms and software are currently being developed and should be implemented shortly to derive the aerosol scattering ratio and aerosol backscattering coefficient from this lidar system. Additional efforts are underway to develop and implement algorithms to directly compute aerosol extinction using the Raman nitrogen return signals. These algorithms are also based on those used for the analyses of data acquired by the GSFC Scanning Raman Lidar during periodic field experiments including:

TARFOX (Tropospheric Aerosol Radiative Forcing Observational Experiment) (http://prometheus.arc.nasa.gov/~tarfox/),

the First (http://www.arm.gov/~info/iops/wv_iop/wv_iop.html) and Second (http://www.arm.gov/docs/iops/1997/sep_integrated/index.html) Water Vapor Intensive Operations Periods, and

CAMEX-III (Convection and Moisture Experiment-III) to be held off the Florida coast in late-summer, 1998.