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Front. Environ. Sci. | doi: 10.3389/fenvs.2019.00094

Retrieving aerosol characteristics from the PACE mission, Part 2: Multi-angle and polarimetry

 Lorraine A. Remer1*,  Kirk D. Knobelspiesse2,  Peng-Wang Zhai3,  Feng Xu4, Olga Kalashnikova4, Jacek Chowdhary5, 6, Otto P. Hasekamp7,  Oleg Dubovik8,  Lianghai Wu7, Ziauddin Ahmad9, 10,  Emmanuel Boss11,  Brian Cairns6*,  Odele Coddington12, Anthony B. Davis4,  Heidi M. Dierssen13*, David J. Diner4,  Bryan A. Franz2,  Robert J. Frouin14,  Bo-Cai Gao15,  Amir Ibrahim9, 16, Robert C. Levy17, J. Vanderlei Martins3, Ali H. Omar18 and Omar Torres19
  • 1Joint Center for Earth system Technology, University of Maryland, Baltimore County, United States
  • 2(NASA) Ocean Ecology Laboratory, Goddard Space Flight Center, United States
  • 3Department of Physics, University of Maryland, Baltimore County, United States
  • 4NASA Jet Propulsion Laboratory (JPL), United States
  • 5Columbia University, United States
  • 6Goddard Institute for Space Studies (NASA), United States
  • 7Earth Science Group, Netherlands Institute for Space Research (NWO), Netherlands
  • 8UMR8518 Laboratoire d'optique atmosphèrique (LOA), France
  • 9Goddard Space Flight Center, United States
  • 10Science Applications International Corporation (United States), United States
  • 11School of Marine Sciences, University of Maine, United States
  • 12Laboratory for Atmospheric and Space Physics, University of Colorado Boulder, United States
  • 13Department of Marine Science, University of Connecticut Groton, United States
  • 14Scripps Institution of Oceanography, University of California, San Diego, United States
  • 15United States Naval Research Laboratory, United States
  • 16Science Systems and Applications (United States), United States
  • 17(NASA) Climate and Radiation Laboratory, Goddard Space Flight Center, United States
  • 18Chemistry and Dynamics Branch, Langley Research Center, United States
  • 19(NASA), Goddard Space Flight Center, United States

The Plankton, Aerosol, Clouds, ocean Ecosystem (PACE) mission presents new opportunities and new challenges in applying observations of two complementary multi-angle polarimeters for the space-based retrieval of global aerosol properties. Aerosol remote sensing from multi-angle radiometric-only observations enables aerosol characterization to a greater degree than single-view radiometers, as demonstrated by nearly two decades of heritage instruments. Adding polarimetry to the multi-angle observations allows for the retrieval of aerosol optical depth, Angstrom exponent, parameters of size distribution, measures of aerosol absorption, complex refractive index and degree of nonsphericity of the particles, as demonstrated by two independent retrieval algorithms applied to the heritage POLarization and Directionality of the Earth’s Reflectance (POLDER) instrument. The reason this detailed particle characterization is possible is because a multi-angle polarimeter measurement contains twice the number of Degrees of Freedom of Signal (DFS) than does an observation from a single-view radiometer. The challenges of making use of this information content involve separating surface signal from atmospheric signal, especially when the surface is optically complex and especially in the ultraviolet portion of the spectrum where we show the necessity of polarization in making that separation. The path forward is likely to involve joint retrievals that will simultaneously retrieve aerosol and surface properties, although advances will be required in radiative transfer modeling and in representing optically complex constituents in those models. Another challenge is in having the processing capability that can keep pace with the output of these instruments in an operational environment. Yet, preliminary algorithms applied to airborne multi-angle polarimeter observations offer encouraging results that demonstrate the advantages of these instruments to retrieve aerosol layer height, particle single scattering albedo, size distribution and spectral optical depth, and also show the necessity of polarization measurements, not just multi-angle radiometric measurements, to achieve these results.

Keywords: aerosol, Multi-angle, Polarimeter, PACE, satellite remote sensing

Received: 30 Nov 2018; Accepted: 03 Jun 2019.

Edited by:

David Antoine, Curtin University, Australia

Reviewed by:

Fischer Juergen, Freie Universität Berlin, Germany
Bertrand Fougnie, European Organisation for the Exploitation of Meteorological Satellites, Germany  

Copyright: © 2019 Remer, Knobelspiesse, Zhai, Xu, Kalashnikova, Chowdhary, Hasekamp, Dubovik, Wu, Ahmad, Boss, Cairns, Coddington, Davis, Dierssen, Diner, Franz, Frouin, Gao, Ibrahim, Levy, Martins, Omar and Torres. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence:
Dr. Lorraine A. Remer, University of Maryland, Baltimore County, Joint Center for Earth system Technology, Baltimore, United States, laremer@hotmail.com
Dr. Brian Cairns, Goddard Institute for Space Studies (NASA), New York, New York, United States, brian.cairns@nasa.gov
Dr. Heidi M. Dierssen, University of Connecticut Groton, Department of Marine Science, Groton, Connecticut, United States, heidi.dierssen@uconn.edu