Retrieving Aerosol Characteristics From the PACE Mission, Part 2: Multi-Angle and Polarimetry

Thumbnail Image

Files

fenvs-07-00094.pdf (2.69 MB)

Links to Files

https://www.frontiersin.org/article/10.3389/fenvs.2019.00094

Permanent Link

https://doi.org/10.3389/fenvs.2019.00094
 http://hdl.handle.net/11603/15883

Collections

UMBC Joint Center for Earth Systems Technology (JCET)
UMBC Faculty Collection
UMBC Physics Department

Author/Creator

Author/Creator ORCID

https://orcid.org/0000-0003-4333-533X
 https://orcid.org/0000-0003-4695-5200

Date

2019-07-23

Type of Work

journal articles
Text

Department

Program

Citation of Original Publication

Remer LA, Knobelspiesse K, Zhai P-W, Xu F, Kalashnikova OV, Chowdhary J, Hasekamp O, Dubovik O, Wu L, Ahmad Z, Boss E, Cairns B, Coddington O, Davis AB, Dierssen HM, Diner DJ, Franz B, Frouin R, Gao B-C, Ibrahim A, Levy RC, Martins JV, Omar AH and Torres O (2019) Retrieving Aerosol Characteristics From the PACE Mission, Part 2: Multi-Angle and Polarimetry. Front. Environ. Sci. 7:94. doi: 10.3389/fenvs.2019.00094

Rights

This work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.
Public Domain Mark 1.0

Subjects

Abstract

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 non-sphericity 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 why this detailed particle characterization is possible is because a multi-angle polarimeter measurement contains twice the number of Degrees of Freedom of Signal (DFS) compared to 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.