Abstract
Lidar ratio for dust aerosols is retrieved from a synergetic use of the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) Total Attenuated Backscatter coefficients and the Moderate Resolution Imaging Spectroradiometer (MODIS) Aerosol Optical Depths (AODs) for 5 years from 2007 to 2011. MODIS AODs from the Dark Target (DT) algorithm over ocean and from the Deep Blue (DB) algorithm over land are used as a constraint for the retrieval. The dust lidar ratio is retrieved larger over land (46.6 ± 36.3 sr) than ocean (39.5 ± 16.8 sr) and shows distinct regional variation. Lidar ratio for Saharan dust (49.5 ± 36.8 sr) is larger than Arabian dust (42.5 ± 26.2 sr). Lidar ratios for dust aerosols transported to Mediterranean Sea (44.4 ± 15.9 sr), Mid Atlantic (40.3 ± 12.4 sr), and Arabian Sea (37.5 ± 12.1 sr) show lower values relative to their source regions. Retrieved dust lidar ratios for Taklamakan and Gobi Deserts region (35.0 ± 31.1 sr) and Australia (35.4 ± 34.4 sr) are slightly lower than the above-mentioned regions. AOD comparison between CALIOP and MODIS shows that the CALIOP AOD is biased low. When including clear air AOD for CALIOP, however, AODs from two sensors become more comparable.
Highlights
The Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) onboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite is a space-borne lidar system measuring vertical profiles of aerosols and clouds over the globe since 2006 [1]
The comparison of CALIOP aerosol optical depths (AODs) with Aerosol Robotic Network (AERONET) and the Moderate Resolution Imaging Spectroradiometer (MODIS) over ocean shows that the AOD differences have decreased [18]
Dust lidar ratios are retrieved by a synergetic use of CALIOP and MODIS products for 5 years from 2007 to 2011
Summary
The Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) onboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite is a space-borne lidar system measuring vertical profiles of aerosols and clouds over the globe since 2006 [1]. While the vertical resolution of aerosol properties provided by the CALIPSO is invaluable, many studies report lower aerosol optical depths (AODs) for CALIOP compared to other space-borne, airborne, or ground-based measurements [3,4,5,6,7,8,9]. The lidar ratio, one of the most important parameter in aerosol extinction retrieval, is estimated to have uncertainty (defined as standard deviation of lidar ratios) at 30–50% in version 3 These have improved in version 4 for some aerosol subtypes such as clean marine, dust, and smoke. Dust lidar ratios are determined from the CALIOP (version 4) measurements by constraining the retrieval with MODIS (collection 6) AOD. By using AOD constrained retrieval, dust lidar ratios are determined globally and regional variability of dust lidar ratio are investigated in this study.
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