Abstract
We are demonstrating on a few cases the capability of CALIPSO to retrieve the 532 nm lidar ratio over the ocean when CloudSat surface scattering cross section is used as a constraint. We are presenting the algorithm used and comparisons with the column lidar ratio retrieved by the NASA airborne high spectral resolution lidar. For the three cases presented here, the agreement is fairly good. The average CALIPSO 532 nm column lidar ratio bias is 13.7% relative to HSRL, and the relative standard deviation is 13.6%. Considering the natural variability of aerosol microphysical properties, this level of accuracy is significant since the lidar ratio is a good indicator of aerosol types. We are discussing dependencies of the accuracy of retrieved aerosol lidar ratio on atmospheric aerosol homogeneity, lidar signal to noise ratio, and errors in the optical depth retrievals. We are obtaining the best result (bias 7% and standard deviation around 6%) for a nighttime case with a relatively constant lidar ratio (in the vertical) indicative of homogeneous aerosol type.
Highlights
Retrievals of aerosol extinction from a backscatter lidar rely on an inversion procedure [1,2,3,4] which is limited by the accuracy of the measurements itself, and by the knowledge of the aerosol microphysical properties
We have developed a new methodology based on Cloud Aerosol Lidar Infrared Pathfinder Satellite Observations (CALIPSO) [6] and CloudSat [7] ocean surface echo to determine the aerosol optical depth (AOD) [8,9] which can be used in combination with CALIPSO vertical backscatter coefficient profiles to retrieve the lidar ratio
We provide a quantitative assessment of the accuracy of our lidar ratio based on a few case studies from coincident underflights with the NASA Langley Research Center (LaRC) airborne High Spectral Resolution Lidar (HSRL), which makes a measurement of the lidar ratio profile [11]
Summary
Retrievals of aerosol extinction from a backscatter lidar rely on an inversion procedure [1,2,3,4] which is limited by the accuracy of the measurements itself, and by the knowledge of the aerosol microphysical properties (size distribution, shape and refractive indices). These determine the so-called “lidar ratio”, referred to as the extinction to backscatter ratio.
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