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Aerosols in OCO-2/GOSAT retrievals of XCO₂: An information content and error analysis

Sanghavi, Suniti and Nelson, Robert and Frankenberg, Christian and Gunson, Michael (2020) Aerosols in OCO-2/GOSAT retrievals of XCO₂: An information content and error analysis. Remote Sensing of Environment, 251 . Art. No. 112053. ISSN 0034-4257. https://resolver.caltech.edu/CaltechAUTHORS:20201217-101454837

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Abstract

We have analyzed the effect of aerosols on the retrieval of the dry air mixing ratio of carbon dioxide (XCO₂) in the Earth's atmosphere from instruments like OCO-2 and GOSAT. High-fidelity simulations of multi-angle spectropolarimetric observations in the O₂ A-band and the weak and strong CO₂ bands are used to evaluate the information contained in different measurement subsets/synergies for the retrieval of aerosol, surface, and molecular parameters. We contrast the biases and uncertainties in the retrieved XCO₂ resulting from the assumption of free or fixed aerosol microphysical parameters in the retrieval algorithm. It is very difficult to achieve the required retrieval accuracy of 0.2% for XCO₂ using intensity-only Nadir mode measurements. The uncertainty in the retrieved XCO₂ can be minimized by introducing multiangle and polarimetric measurement synergies. While the retrieval bias on XCO₂ is practically eliminated by the addition of measurement synergies for free aerosol microphysical parameters, fixed aerosol retrievals can lead to an increase in XCO₂ bias. In both cases, our full multi-angle polarimetric dataset produces a maximum uncertainty of ~1.6% in the retrieved XCO₂ at low aerosol optical thicknesses and over dark surfaces. The XCO₂ retrieval uncertainty improves to better than 0.2% at greater aerosol optical thickness and brighter surfaces. The problematic low aerosol optical thickness and low surface brightness regime produces an XCO₂ bias of 1 − 8 % for fixed aerosol microphysics, while the free parameters produce a maximum bias well under 10⁻³% for all retrieval scenes considered.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1016/j.rse.2020.112053DOIArticle
ORCID:
AuthorORCID
Sanghavi, Suniti0000-0003-0754-9154
Nelson, Robert0000-0002-3471-5683
Frankenberg, Christian0000-0002-0546-5857
Alternate Title:Aerosols in OCO-2/GOSAT retrievals of XCO2: An information content and error analysis
Additional Information:© 2020 Published by Elsevier Inc. Received 12 February 2020, Revised 12 August 2020, Accepted 16 August 2020, Available online 29 August 2020. The authors thank three anonymous reviewers for their inputs which helped improve the quality of our manuscript. We are grateful to Dr. Eugene Ustinov, Dr. Jonathan Hobbs and Dr. Brian Drouin of the Jet Propulsion Laboratory for stimulating discussions. This work was funded by OCO-2 Phase E. The research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004). © 2020. California Institute of Technology. Government sponsorship acknowledged. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Funders:
Funding AgencyGrant Number
NASA/JPL/CaltechUNSPECIFIED
NASA80NM0018D0004
Subject Keywords:OCO-2; XCO₂; Aerosol; O₂ A-band; Weak and strong CO₂ bands; Polarimetry; Multi-angle viewing; Climatology
Record Number:CaltechAUTHORS:20201217-101454837
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20201217-101454837
Official Citation:Suniti Sanghavi, Robert Nelson, Christian Frankenberg, Michael Gunson, Aerosols in OCO-2/GOSAT retrievals of XCO2: An information content and error analysis, Remote Sensing of Environment, Volume 251, 2020, 112053, ISSN 0034-4257, https://doi.org/10.1016/j.rse.2020.112053.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:107149
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:17 Dec 2020 19:29
Last Modified:17 Dec 2020 19:29

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