1. Channel Selection for CO 2 Retrieval Using Near Infrared Measurements EGU 2009 Le Kuai 1, Vijay Natraj 1, Run-Lie Shia 1, Susan Kulawik 2, Kevin Bowman 2, Charles Miller 2, Bill Irion 2, Yuk Yung 1 1. Division of Geological and Planetary Sciences, California Institute of Technology 2. Jet Propulsion Laboratory, California Institute of Technology

2. Abstract Understanding changes in the concentrations, global sources and sinks, dynamics and other processes that control the variability of atmospheric carbon dioxide (CO2) has emerged as one of the principal challenges of 21st century Earth system science. Satellite observations of atmospheric CO2 are poised to revolutionize our understanding of global carbon cycle science by providing unprecedented spatiotemporal resolution and coverage. Here, we carry out an information content analysis for CO2 retrieval from near infrared (NIR) bands (GOSAT). Since NIR measurements are sensitive to changes in the lower troposphere, CO2 sources and sinks near the surface are more detectable using NIR measurements. GOSAT will measure reflected sunlight in three NIR spectral regions (the 0.76 μm O2 A-band and two CO2 bands at 1.61 and 2.06μm). Information analysis provides a method to choose the first 200 out of 1016 channels in each CO2 band with the highest information content. Retrieval using these 200 channels in each band could provide as much as 90% information as a retrieval using all 1016 channels in each band.

3. CO2 Weighting function Clear sky case WCO2 SCO2

4. 1)Clear sky case 2) High AOD, high COD case Fig. 2 First 20 channels with highest IC. Red: most sensitive to CO 2 ; blue: most sensitive to temperature. Left is clear sky case and right is the cloudy sky case.

5. Fig. 3 Channels with highest information content (CO 2 ) are from the channels with intermediate radiance in both bands. Left is clear sky case and right is the cloudy sky case. 1)Clear sky case 2) High AOD, high COD case

9. Conclusions 1) Information analysis to select channels 2) The intermediate channels provide most information. 3) The high DOF and IC for high AOD and high COD scenarios from backscattering by aerosols. 4) No influence of scenarios on the channels selection. 5) The first 200 channels (in order of IC) in each band capture more than 90% 6) Most sensitive to CO 2 and least sensitive to other parameters.