Ninth ARM Science Team Meeting Proceedings, San Antonio, Texas, March 22-26, 1999 1 Determination of Cloud Base Height Using the GSFC Raman Lidar B. B. Demoz, K. D. Evans, M. Cadirola, and S. H. Melfi University of Maryland, Baltimore County Baltimore, Maryland D. O’C. Starr, D. N. Whiteman, and G. Schwemmer National Aeronautics and Space Administration Goddard Space Flight Center Greenbelt, Maryland D. L. Hlavka and J. R. Campbell Science Systems and Applications, Inc. Greenbelt, Maryland D. D. Turner Pacific Northwest National Laboratory Richland, Washington Introduction Exact determination of cloud geometry is important in climate and radiation studies. The derivation of cloud optical depth, for example, requires accurate determination of cloud base height (CBH) and top height. Recent studies by Kogan and Kogan (1998) suggest that variations in cloud boundary (base and top heights) may be more important than variations in cloud microstructure for the calculation of cloud optical depth. They report that neglect of irregular cloud boundary (slab assumption) could lead to 20% to 45% errors in optical depth calculations. Further, Pincus et al. (1999) report that cloud top is “uncorrelated with optical thickness,” suggesting that CBH and/or cloud droplet concentration may be the primary controlling factor. Moreover, Han and Ellingson (1997) indicate that the major uncertainty in the calculation of downwelling longwave flux at the surface may be due to errors in determining cloud thickness. Thus, an accurate characterization of CBH is required. This study reports on determination of CBH using the Goddard Space Flight Center (GSFC) Scanning Raman Lidar (SRL). We focus on the advantages the SRL introduces in the determination of CBH in comparison to determinations made using data from the Micropulse Lidar (MPL), Belfort Laser Ceilometer (BLC), and Millimeter-Wavelength Cloud Radar (MMCR). The SRL observations provide quantitative Aerosol Scattering Ratio (ASR), water vapor mixing ratio (W), and relative humidity (RH, derived quantity) profiles not available from the other sensors. Data from the U.S. Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Program’s Cloud and Radiation Testbed (CART) site and other experiment campaigns are utilized.