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Published June 2010 | public
Journal Article

Channel selection using information content analysis: A case study of CO_2 retrieval from near infrared measurements


A major challenge in retrieving CO_2 concentrations from thermal infrared remote sensing comes from the fact that measurements in the 4.3 and 15 μm absorption bands (AIRS or TES) are sensitive to both temperature and CO_2 variations. This complicates the selection of absorption channels with maximum CO_2 concentration information content. In contrast, retrievals using near infrared (NIR) CO_2 absorption bands are relatively insensitive to temperature and are most sensitive to changes of CO_2 near the surface, where the sources and sinks are located. The Orbiting Carbon Observatory (OCO) was built to measure reflected sunlight in three NIR spectral regions (the 0.76 μm O_2 A-band and two CO_2 bands at 1.61 and 2.06 μm). In an effort to significantly increase the speed of accurate CO_2 retrieval algorithms for OCO, we performed an information content analysis to identify the 20 best channels from each CO_2 spectral region to use in OCO retrievals. Retrievals using these 40 channels provide as much as 75% of the total CO_2 information content compared to retrievals using all 1016 channels in each spectral region. The CO_2 retrievals using our selected channels have a precision better than 0.1 ppm. This technique can be applied to the retrieval of other geophysical variables (e.g., temperature or CH_4), or modified for other instruments, such as AIRS or TES.

Additional Information

© 2010 Elsevier Ltd. Received 30 October 2009, Revised 21 February 2010, Accepted 22 February 2010, Available online 26 February 2010. Special Issue Dedicated to Laurence S. Rothman on the Occasion of his 70th Birthday. This research is supported by the Orbiting Carbon Observatory (OCO) project, a NASA Earth System Science Pathfinder (ESSP) mission. The authors would like to thank Denis O'Brien, Igor Polonsky and Chris O'Dell from Colorado State University for providing us the orbit simulator code and for helping with its development and maintenance, and James McDuffie from the Jet Propulsion Laboratory (JPL) for providing covariance information.

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