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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Volume 9, issue 10
Atmos. Meas. Tech., 9, 5053–5062, 2016
https://doi.org/10.5194/amt-9-5053-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Atmos. Meas. Tech., 9, 5053–5062, 2016
https://doi.org/10.5194/amt-9-5053-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 14 Oct 2016

Research article | 14 Oct 2016

Validating MODIS above-cloud aerosol optical depth retrieved from “color ratio” algorithm using direct measurements made by NASA's airborne AATS and 4STAR sensors

Hiren Jethva1,2, Omar Torres2, Lorraine Remer3, Jens Redemann4, John Livingston5, Stephen Dunagan4, Yohei Shinozuka6, Meloe Kacenelenbogen6, Michal Segal Rosenheimer6, and Rob Spurr7 Hiren Jethva et al.
  • 1Universities Space Research Association, Goddard Earth Sciences Technology and Research (GESTAR), Columbia, MD 21044, USA
  • 2Earth Science Division, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
  • 3Joint Center for Earth Systems Technology, University of Maryland, Baltimore County, Baltimore, MD 21250, USA
  • 4Earth Science Division, NASA Ames Research Center, Moffett Field, CA 94035, USA
  • 5SRI International, Menlo Park, CA 94025, USA
  • 6Bay Area Environmental Research Institute, NASA Ames Research Center, Moffett Field, CA 94035, USA
  • 7RT Solutions, Cambridge, MA 02138, USA

Abstract. We present the validation analysis of above-cloud aerosol optical depth (ACAOD) retrieved from the “color ratio” method applied to MODIS cloudy-sky reflectance measurements using the limited direct measurements made by NASA's airborne Ames Airborne Tracking Sunphotometer (AATS) and Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research (4STAR) sensors. A thorough search of the airborne database collection revealed a total of five significant events in which an airborne sun photometer, coincident with the MODIS overpass, observed partially absorbing aerosols emitted from agricultural biomass burning, dust, and wildfires over a low-level cloud deck during SAFARI-2000, ACE-ASIA 2001, and SEAC4RS 2013 campaigns, respectively. The co-located satellite-airborne matchups revealed a good agreement (root-mean-square difference  <  0.1), with most matchups falling within the estimated uncertainties associated the MODIS retrievals (about −10 to +50 %). The co-retrieved cloud optical depth was comparable to that of the MODIS operational cloud product for ACE-ASIA and SEAC4RS, however, higher by 30–50 % for the SAFARI-2000 case study. The reason for this discrepancy could be attributed to the distinct aerosol optical properties encountered during respective campaigns. A brief discussion on the sources of uncertainty in the satellite-based ACAOD retrieval and co-location procedure is presented. Field experiments dedicated to making direct measurements of aerosols above cloud are needed for the extensive validation of satellite-based retrievals.

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Validation of the above-cloud aerosol optical depth retrieved using the "color ratio" method applied to MODIS cloudy-sky measurements against airborne direct measurements made by NASA’s AATS and 4STAR sun photometers during SAFARI-2000, ACE-ASIA 2001, and SEAC4RS 2013 reveals a good level of agreement (difference < 0.1), in which most matchups are found be constrained within the estimated uncertainties associated with the MODIS retrievals (-10 % to +50 %).
Validation of the above-cloud aerosol optical depth retrieved using the "color ratio" method...
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