1. 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: ,
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
CO 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), , 2004.
[2] V. Natraj and R.J.D. Spurr, J. Quant. Spectrosc. Radiat. Transfer, 107(2), , 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 (low altitude); AOD = 0.05, COD = 0.25; AOD = 0.25, COD = 0.05