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Published January 11, 2012 | Published + Erratum
Journal Article Open

The ACOS CO_2 retrieval algorithm – Part 1: Description and validation against synthetic observations


This work describes the NASA Atmospheric CO_2 Observations from Space (ACOS) X_(CO_2) retrieval algorithm, and its performance on highly realistic, simulated observations. These tests, restricted to observations over land, are used to evaluate retrieval errors in the face of realistic clouds and aerosols, polarized non-Lambertian surfaces, imperfect meteorology, and uncorrelated instrument noise. We find that post-retrieval filters are essential to eliminate the poorest retrievals, which arise primarily due to imperfect cloud screening. The remaining retrievals have RMS errors of approximately 1 ppm. Modeled instrument noise, based on the Greenhouse Gases Observing SATellite (GOSAT) in-flight performance, accounts for less than half the total error in these retrievals. A small fraction of unfiltered clouds, particularly thin cirrus, lead to a small positive bias of ~0.3 ppm. Overall, systematic errors due to imperfect characterization of clouds and aerosols dominate the error budget, while errors due to other simplifying assumptions, in particular those related to the prior meteorological fields, appear small.

Additional Information

© 2012 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. The authors wish to thank two anonymous reviewers for their constructive suggestions and insightful comments. We would like to thank several colleagues for work they have done that has helped this project: Bashwar Sen for early algorithm management, Linda Brown for spectroscopy development, Rob Spurr for help with the radiative transfer, Lukas Mandrake for GOSAT data analysis, and Ross Salawitch for many useful discussions. A portion 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. The Colorado State University contributions to this work were carried out under NASA contract 1380533.


We would like to inform you that there were two mistakes in the author list of this manuscript. The initial of the author Eldering was wrong and the author Crisp was missing in the author list. Above you will find the correct author list.

Attached Files

Published - amt-5-99-2012.pdf

Erratum - amt-5-193-2012.pdf


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