A Two Orders of Scattering Approach to Account for Polarization in Near Infrared Retrievals

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Page 1 1 of 21, 28th Review of Atmospheric Transmission Models, 6/14/2006 A Two Orders of Scattering Approach to Account for Polarization in Near Infrared Retrievals Vijay Natraj, Hartmut Bösch and Yuk L. Yung
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A Two Orders of Scattering Approach to Account for Polarization in Near Infrared Retrievals Vijay Natraj, Hartmut B ö sch and Yuk L. Yung. Importance of Polarization. Polarization is a result of scattering. - PowerPoint PPT Presentation

Transcript of A Two Orders of Scattering Approach to Account for Polarization in Near Infrared Retrievals

OCO Mission Operations OverviewA Two Orders of Scattering Approach to Account
for Polarization in Near Infrared Retrievals
Vijay Natraj, Hartmut Bösch and Yuk L. Yung
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Importance of Polarization
Polarization is a result of scattering.
The Earth’s atmosphere contains molecules, aerosols and clouds, all of which contribute to scattering.
Surfaces can also polarize, in some cases significantly (e.g., ocean).
Polarization depends on solar and viewing angles and will therefore introduce spatial biases in retrieved trace gas column densities if unaccounted for.
The satellite instrument could be sensitive to polarization.
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Polarization in the O2 A Band
continuum
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Proposed Solution: Two Orders of Scattering Approximation
Full multiple-scattering vector ARTM codes (e.g. VLIDORT) are too slow to meet large-scale operational processing requirements.
Scalar computation causes two kinds of errors.
polarized component of the Stokes vector is neglected.
correction to intensity due to polarization is neglected.
Major contribution to polarization comes from first few orders of scattering (multiple scattering is depolarizing).
Single scattering does not account for the correction to intensity due to polarization.
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Polarization Approximation Overview
Retrievals will only be applied to optically thin scattering (τ<0.3).
Intensity will still be calculated with full multiple scattering scalar model.
S = Isca+Icor-Q2
Exact through second order
Simple model, easily implemented
Case Study: Orbiting Carbon Observatory (OCO) Mission
First global, space-based observations of atmospheric CO2
high accuracy, resolution and coverage
geographic distribution of CO2 sources and sinks and variability
High resolution spectroscopic measurements of reflected sunlight
NIR CO2 and O2 bands
Remote sensing retrieval algorithms
accuracies near 0.3% (1 ppm)
Chemical transport models
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OCO Spectroscopy
Column-integrated CO2 abundance => Maximum contribution from surface
High resolution spectroscopic measurements of reflected sunlight in near IR CO2 and O2 bands
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Scenarios for Testing Proposed Method
SZA: 10°, 40°, 70°
Azimuth: 0° (OCO nadir mode), 45°, 90°, 135°, 180°
Surface Albedo: 0.01, 0.1, 0.3
Aerosol OD: 0 (Rayleigh), 0.01, 0.1
Dusty continental aerosol (Kahn et al., JGR 106(D16), pp. 18219-18238, 2001)
45 geometries
9 scenarios
Forward Model Radiance Errors: O2 A Band
Asterisks refer to different geometries; The red triangles refer to OCO nadir viewing geometry.
Rayleigh
Forward Model Radiance Errors: 1.61 µm CO2 Band
Asterisks refer to different geometries; The red triangles refer to OCO nadir viewing geometry.
Rayleigh
Forward Model Radiance Errors: 2.06 µm CO2 Band
Asterisks refer to different geometries; The red triangles refer to OCO nadir viewing geometry.
Rayleigh
Residuals: Best Case Scenario (O2 A Band)
SZA = 10°; VZA = 0°; Azimuth = 0°; Surface Albedo = 0.3; No Aerosol
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Residuals: Best Case Scenario (1.61 µm CO2 Band)
SZA = 10°; VZA = 0°; Azimuth = 0°; Surface Albedo = 0.3; No Aerosol
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Residuals: Best Case Scenario (2.06 µm CO2 Band)
SZA = 10°; VZA = 0°; Azimuth = 0°; Surface Albedo = 0.3; No Aerosol
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Residuals: Worst-Case Scenario (O2 A Band)
SZA = 70°; VZA = 70°; Azimuth = 90°; Surface Albedo =0.01; Aerosol OD = 0.1
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Residuals: Worst-Case Scenario (1.61 µm CO2 Band)
SZA = 70°; VZA = 70°; Azimuth = 90°; Surface Albedo =0.01; Aerosol OD = 0.1
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Residuals: Worst-Case Scenario (2.06 µm CO2 Band)
SZA = 70°; VZA = 70°; Azimuth = 90°; Surface Albedo =0.01; Aerosol OD = 0.1
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Timing Results
50% overhead to scalar calculation
VLIDORT optimized for multiple geometry calculations
For real retrievals, overhead expected to be ~ 10%
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Linear Error Analysis
6 scenarios considered
Aerosol OD: 0.01, 0.1
8 half-space streams, 11 layers
Number of spectral points: 8307 (O2 A band), 3334 (CO2 bands)
G001_A001
G001_A01
G01_A001
G01_A01
G03_A001
G03_A01
Further Work
Spectral binning
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Summary