Assessment of errors and biases in retrievals of X_(CO2), X_(CH4), X_(CO), and X_(N2O) from a 0.5 cm^(-1) resolution solar-viewing spectrometer
Abstract
Bruker™ EM27/SUN instruments are commercial mobile solar-viewing near-IR spectrometers. They show promise for expanding the global density of atmospheric column measurements of greenhouse gases and are being marketed for such applications. They have been shown to measure the same variations of atmospheric gases within a day as the high-resolution spectrometers of the Total Carbon Column Observing Network (TCCON). However, there is little known about the long-term precision and uncertainty budgets of EM27/SUN measurements. In this study, which includes a comparison of 186 measurement days spanning 11 months, we note that atmospheric variations of X_(gas) within a single day are well captured by these low-resolution instruments, but over several months, the measurements drift noticeably. We present comparisons between EM27/SUN instruments and the TCCON using GGG as the retrieval algorithm. In addition, we perform several tests to evaluate the robustness of the performance and determine the largest sources of errors from these spectrometers. We include comparisons of X_(CO2), X_(CH4), X_(CO), and X_(N2)O. Specifically we note EM27/SUN biases for January 2015 of 0.03, 0.75, –0.12, and 2.43 % for X_(CO2), X_(CH4), X_(CO), and X_(N2)O respectively, with 1σ running precisions of 0.08 and 0.06 % for X_(CO2) and X_(CH4) from measurements in Pasadena. We also identify significant error caused by nonlinear sensitivity when using an extended spectral range detector used to measure CO and N_2O.
Additional Information
© 2016 Author(s). This work is distributed under the Creative Commons Attribution 3.0 License. Published by Copernicus Publications on behalf of the European Geosciences Union. Received: 05 Feb 2016 – Discussion started: 04 Mar 2016. Revised: 24 Jun 2016 – Accepted: 28 Jun 2016 – Published: 03 Aug 2016. We thank Frank Hase and Michael Gisi for helpful discussions on ghost reduction, detector nonlinearity, and ILS measurements. We further thank Michael Gisi and Bruker Optics™ for loaning us a standard InGaAs detector for testing and for instructions on realigning the EM27/SUN. We thank Dietrich Feist for discussions on mirror degradation. We also thank Nicholas Jones, David Giffith, Frank Hase, and Sabrina Arnold for sharing their experience with mirror degradation. This work is supported in part by the W. M. Keck Institute for Space Studies. Jacob Hedelius was also partially supported by a Caltech Chemistry and Chemical Engineering Division Fellowship funded by the Dow Chemical Graduate Fellowship, and expresses thanks to them. The authors gratefully acknowledge funding from the NASA Carbon Cycle Science program (grant number NNX14AI60G) and the Jet Propulsion Laboratory. Manvendra K. Dubey acknowledges funding from the NASA-CMS program for field observations and from the LANL-LDRD for the acquisition of the LANL EM27/SUN. Jia Chen, Taylor Jones, Jonathan E. Franklin, and Steven C. Wofsy acknowledge funding provided by NSF MRI Award 1337512. The authors thank the referees for their comments. The authors declare that they have no conflict of interest.Attached Files
Published - amt-9-3527-2016.pdf
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Additional details
- Eprint ID
- 82434
- Resolver ID
- CaltechAUTHORS:20171017-154006422
- Keck Institute for Space Studies (KISS)
- Dow Chemical Company
- NNX14AI60G
- NASA
- JPL
- AGS-1337512
- NSF
- Los Alamos National Laboratory
- Created
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2017-10-17Created from EPrint's datestamp field
- Updated
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2021-11-15Created from EPrint's last_modified field
- Caltech groups
- Keck Institute for Space Studies, Division of Geological and Planetary Sciences