Polarization Effects on Column CO2 Retrievals from Non-Nadir Satellite Measurements in the Short-Wave Infrared Vijay Natraj1, Hartmut Bösch2, Robert J.D. Spurr3, Yuk L. Yung1 1Department of Planetary Sciences, California Institute of Technology, Pasadena, CA, USA 2Department of Physics and Astronomy, University of Leicester, Leicester, UK 3RT Solutions, Inc., Cambridge, MA, USA Contact: Vijay Natraj, Phone: +1-626-395-6962, Email: vijay@gps.caltech.edu A51A-0091 Introduction Greenhouse Gases Observation Satellite (GOSAT): successful Orbiting Carbon Observatory (OCO): to be rebuilt (?) Quantify sources and sinks of CO2 using precise column abundance measurements Reflected sunlight at the top of the atmosphere (TOA) Spectrometers sensitive to atmospheric polarization. Need to consider polarization in modeling of atmospheric radiative transfer (RT). O2 A-band CO2 1.61m CO2 2.06 m Scenarios: Target Mode Observations of fixed ground target Validations of space-based observations with coincident ground-based column measurements Aerosol/Cirrus: Same as for glint Scattering angle: 85°-150° XCO2 Errors: Target Mode Figure 6: XCO2 Errors for (left) scalar model (right) R-2OS model XCO2 Errors: Glint Mode Conclusions Scalar Largest errors for low AOD/COD Low order scattering is highly polarized 2OS 1-2 orders of magnitude smaller XCO2 errors than scalar model Thin cirrus modeled well Largest errors for optically thick aerosol scenarios Polarized multiple scattering causes large errors XCO2 errors Forward model error compensated by changing CO2 Relative magnitude of CO2 Jacobians and forward model errors determines XCO2 error Error compensation when all variables retrieved simultaneously Figure 2: XCO2 Errors for (left) scalar model (right) R-2OS model Figure 1: OCO Spectral Regions R-2OS Model Fast polarization correction algorithm Assume that only two scattering events (two orders of scattering, 2OS) contribute to polarization 2OS model used in conjunction with scalar RT model Radiant (R) to simulate OCO backscatter measurements Isca, Icor : intensity with polarization neglected, scalar-vector intensity correction I, Q, U: Stokes parameters Figure 3: XCO2 Errors for CO2-only retrievals Figure 4: (top) Forward Model Errors (bottom) CO2 Jacobians Black: AOD = 0.3, Red: AOD = 0.3 (high altitude); Blue: COD = 0.3 SZA = 40° References [1] D. Crisp, et al., Adv. Space Res., 34(4), 700-709, 2004. [2] V. Natraj and R.J.D. Spurr, J. Quant. Spectrosc. Radiat. Transfer, 107(2), 263-293, 2007. [3] V. Natraj, et al., J. Geophys. Res., 113, D11212, 2008. [4] S. Chandrasekhar, Radiative Transfer, 1960. [5] C. D. Rodgers, Inverse Methods for Atmospheric Sounding, 2000. Figure 5: Correlation Coefficients (SZA = 40°) State Vector: 1-19: CO2 20: H2O scaling 21: Surface pressure 22-40: Temperature 41-59: Aerosol 60: Wind speed Surface pressure and wind speed are correlated Scenarios: Glint Mode Sunglint over ocean High signal to noise ratio (SNR) over ocean SZA: 20°, 30°, 40°, 50°, 60°, 65°, 70°, 75° Aerosol/Cirrus: AOD = 0.05, 0.3, 0.3 (high altitude); COD = 0.05, 0.3, 0.3 (low altitude); AOD = 0.05, COD = 0.25; AOD = 0.25, COD = 0.05