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Characterization of the OCO-2 instrument line shape functions using on-orbit solar measurements

Sun, Kang and Liu, Xiong and Nowlan, Caroline R. and Cai, Zhaonan and Chance, Kelly and Frankenberg, Christian and Lee, Richard A. M. and Pollock, Randy and Rosenberg, Robert and Crisp, David (2017) Characterization of the OCO-2 instrument line shape functions using on-orbit solar measurements. Atmospheric Measurement Techniques, 10 (3). pp. 939-953. ISSN 1867-8548. doi:10.5194/amt-10-939-2017.

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Accurately characterizing the instrument line shape (ILS) of the Orbiting Carbon Observatory-2 (OCO-2) is challenging and highly important due to its high spectral resolution and requirement for retrieval accuracy (0. 25 %) compared to previous spaceborne grating spectrometers. On-orbit ILS functions for all three bands of the OCO-2 instrument have been derived using its frequent solar measurements and high-resolution solar reference spectra. The solar reference spectrum generated from the 2016 version of the Total Carbon Column Observing Network (TCCON) solar line list shows significant improvements in the fitting residual compared to the solar reference spectrum currently used in the version 7 Level 2 algorithm in the O₂ A band. The analytical functions used to represent the ILS of previous grating spectrometers are found to be inadequate for the OCO-2 ILS. Particularly, the hybrid Gaussian and super-Gaussian functions may introduce spurious variations, up to 5 % of the ILS width, depending on the spectral sampling position, when there is a spectral undersampling. Fitting a homogeneous stretch of the preflight ILS together with the relative widening of the wings of the ILS is insensitive to the sampling grid position and accurately captures the variation of ILS in the O₂ A band between decontamination events. These temporal changes of ILS may explain the spurious signals observed in the solar-induced fluorescence retrieval in barren areas.

Item Type:Article
Related URLs:
URLURL TypeDescription
Sun, Kang0000-0002-9930-7509
Nowlan, Caroline R.0000-0002-8718-9752
Chance, Kelly0000-0002-7339-7577
Frankenberg, Christian0000-0002-0546-5857
Lee, Richard A. M.0000-0001-6509-697X
Rosenberg, Robert0000-0002-0459-4630
Crisp, David0000-0002-4573-9998
Additional Information:© Author(s) 2017. This work is distributed under the Creative Commons Attribution 3.0 License. Published by Copernicus Publications on behalf of the European Geosciences Union. Received: 08 Oct 2016 – Discussion started: 14 Nov 2016 – Revised: 22 Feb 2017 – Accepted: 24 Feb 2017 – Published: 10 Mar 2017. This study was supported by the NASA OCO-2 science team (NNX12AH38G) and the Smithsonian Institution. We acknowledge Geoffrey Toon at JPL for making the high-resolution solar spectra generated from newer versions of the solar line list available. We also thank Gonzalo Gonzalez Abad at the Smithsonian Astrophysical Observatory (SAO); Debra Wunch at Caltech; Steffen Beirle at the Max Planck Institute for Chemistry (MPI-C); and James McDuffie, Lars Chapsky, Gregory Osterman, and Brendan Fisher at JPL for helpful discussions. Part of the research described in this paper was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. Data availability: The results in this study are based on NASA OCO-2 L1B data products, which are publicly available at The authors declare that they have no conflict of interest. Edited by: F. Hase. Reviewed by: two anonymous referees.
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Smithsonian InstitutionUNSPECIFIED
Issue or Number:3
Record Number:CaltechAUTHORS:20200528-074430950
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Official Citation:Sun, K., Liu, X., Nowlan, C. R., Cai, Z., Chance, K., Frankenberg, C., Lee, R. A. M., Pollock, R., Rosenberg, R., and Crisp, D.: Characterization of the OCO-2 instrument line shape functions using on-orbit solar measurements, Atmos. Meas. Tech., 10, 939–953,, 2017
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:103510
Deposited By: Tony Diaz
Deposited On:28 May 2020 16:35
Last Modified:16 Nov 2021 18:22

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