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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Volume 11, issue 1 | Copyright

Special issue: Holistic Analysis of Aerosol in Littoral Environments - A...

Atmos. Meas. Tech., 11, 499-514, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 24 Jan 2018

Research article | 24 Jan 2018

Minimum aerosol layer detection sensitivities and their subsequent impacts on aerosol optical thickness retrievals in CALIPSO level 2 data products

Travis D. Toth1, James R. Campbell2, Jeffrey S. Reid2, Jason L. Tackett3, Mark A. Vaughan4, Jianglong Zhang1, and Jared W. Marquis1 Travis D. Toth et al.
  • 1Dept. of Atmospheric Sciences, University of North Dakota, Grand Forks, ND, USA
  • 2Aerosol and Radiation Sciences Section, Marine Meteorology Division, Naval Research Laboratory, Monterey, CA, USA
  • 3Science Systems and Applications, Inc., Hampton, VA, USA
  • 4NASA Langley Research Center, Hampton, VA, USA

Abstract. Due to instrument sensitivities and algorithm detection limits, level 2 (L2) Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) 532nm aerosol extinction profile retrievals are often populated with retrieval fill values (RFVs), which indicate the absence of detectable levels of aerosol within the profile. In this study, using 4 years (2007–2008 and 2010–2011) of CALIOP version 3 L2 aerosol data, the occurrence frequency of daytime CALIOP profiles containing all RFVs (all-RFV profiles) is studied. In the CALIOP data products, the aerosol optical thickness (AOT) of any all-RFV profile is reported as being zero, which may introduce a bias in CALIOP-based AOT climatologies. For this study, we derive revised estimates of AOT for all-RFV profiles using collocated Moderate Resolution Imaging Spectroradiometer (MODIS) Dark Target (DT) and, where available, AErosol RObotic NEtwork (AERONET) data. Globally, all-RFV profiles comprise roughly 71% of all daytime CALIOP L2 aerosol profiles (i.e., including completely attenuated profiles), accounting for nearly half (45%) of all daytime cloud-free L2 aerosol profiles. The mean collocated MODIS DT (AERONET) 550nm AOT is found to be near 0.06 (0.08) for CALIOP all-RFV profiles. We further estimate a global mean aerosol extinction profile, a so-called noise floor, for CALIOP all-RFV profiles. The global mean CALIOP AOT is then recomputed by replacing RFV values with the derived noise-floor values for both all-RFV and non-all-RFV profiles. This process yields an improvement in the agreement of CALIOP and MODIS over-ocean AOT.

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