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, UK3RT Solutions, Inc., Cambridge, MA, USA

Contact: Vijay Natraj, Phone: +1-626-395-6962, Email: vijay@gps.caltech.edu

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°

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

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.

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 1.61m

CO2 2.06 m

Figure 1: OCO Spectral Regions

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I = Isca + Icor

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Q = Q2OS

U = U2OS

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

Interplay between CO2 Jacobians and forward model errors

Forward model error compensated by changing CO2

•CO2 Jacobians larger for aerosol than cirrus

Aerosol extinction decreases significantly with wavelength Cirrus extinction remains more or less constant with wavelength

•Forward model error larger for aerosol than cirrus Aerosol particles small and scatter less => low order (> 2)

scattering Cirrus larger and scatters more => multiple scattering

•Error compensation when all variables retrieved simultaneously

XCO2 Errors: Target Mode

Figure 6: XCO2 Errors for (left) scalar model (right) R-2OS model

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

Figure 2: XCO2 Errors for (left) scalar model (right) R-2OS model

Figure 3: XCO2 Errors forCO2-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°

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