X_(CO2) retrieval error over deserts near critical surface albedo
Abstract
Large retrieval errors in column‐weighted CO_2 mixing ratio (X_(CO2)) over deserts are evident in the Orbiting Carbon Observatory 2 version 7 L2 products. We argue that these errors are caused by the surface albedo being close to a critical surface albedo (α_c). Over a surface with albedo close to α_c, increasing the aerosol optical depth (AOD) does not change the continuum radiance. The spectral signature caused by changing the AOD is identical to that caused by changing the absorbing gas column. The degeneracy in the retrievals of AOD and X_(CO2) results in a loss of degrees of freedom and information content. We employ a two‐stream‐exact single scattering radiative transfer model to study the physical mechanism of X_(CO2) retrieval error over a surface with albedo close to α_c. Based on retrieval tests over surfaces with different albedos, we conclude that over a surface with albedo close to α_c, the X_(CO2) retrieval suffers from a significant loss of accuracy. We recommend a bias correction approach that has significantly improved the X_(CO2) retrieval from the California Laboratory for Atmospheric Remote Sensing data in the presence of aerosol loading.
Additional Information
©2016. The Authors. This is an open access article under the terms of the Creative Commons Attribution‐NonCommercial‐NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non‐commercial and no modifications or adaptations are made. Received 21 OCT 2015. Accepted 28 DEC 2015. Accepted article online 3 JAN 2016. Published online 3 FEB 2016. We thank A. Eldering, M. Gunson, V. Natraj, J. Margolis, S. Newman, and K.‐F. Li for their helpful comments. We also thank the Editor, F.C. Seidel, and an anonymous reviewer whose comments helped improve the manuscript significantly. This research was supported in part by NASA grant NNX13AK34G to the California Institute of Technology, a grant from the OCO 2 mission at Jet Propulsion Laboratory, and the KISS program at Caltech. The OCO 2 data used in this study can be downloaded from http://oco.jpl.nasa.gov/science/ocodatacenter/.Attached Files
Published - Zhang_et_al-2016-Earth_and_Space_Science.pdf
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Additional details
- Alternative title
- XCO2 retrieval error over deserts near critical surface albedo
- Eprint ID
- 91290
- Resolver ID
- CaltechAUTHORS:20181128-113131152
- NNX13AK34G
- NASA
- OCO-2 Project
- Keck Institute for Space Studies (KISS)
- Created
-
2018-11-28Created from EPrint's datestamp field
- Updated
-
2021-11-16Created from EPrint's last_modified field
- Caltech groups
- Keck Institute for Space Studies, Division of Geological and Planetary Sciences