1. The Orbiting Carbon Observatory Mission: Effects of Polarization on Retrievals Vijay Natraj Advisor: Yuk Yung Collaborators: Robert Spurr (RT Solutions, Inc.), Hartmut Boesch (JPL), Yibo Jiang (JPL)

2. Welcome-2 Outline Introduction Retrieval Strategy Radiative Transfer Essentials O 2 A Band Results Sensitivity Analysis Outlook

3. Welcome-3 Introduction Atmospheric levels of CO 2 have risen from ~ 270 ppm in 1860 to ~370 ppm today. Since 1860, global mean surface temperature has risen ~1.0 °C with a very abrupt increase since 1980. Does increasing atmospheric CO 2 drive increases in global temperature? Do increasing temperatures increase atmospheric CO 2 levels?

4. Welcome-4 Where are the Missing Carbon Sinks? Only half of the CO 2 released into the atmosphere since 1970 has remained there. The rest has been absorbed by land ecosystems and oceans What are the relative roles of the oceans and land ecosystems in absorbing CO 2 ? Is there a northern hemisphere land sink? What are the relative roles of North America and Eurasia? What controls carbon sinks? Why does the atmospheric buildup vary with uniform emission rates? How will sinks respond to climate change? Reliable climate predictions require an improved understanding of CO 2 sinks Future atmospheric CO 2 increases Their contributions to global change

5. Welcome-5 Why Measure CO 2 from Space? Improved CO 2 Flux Inversion Capabilities Rayner & O’Brien, Geophys. Res. Lett. 28, 175 (2001) Current State of Knowledge Global maps of carbon flux errors for 26 continent/ocean-basin-sized zones retrieved from inversion studies Studies using data from the 56 GV-CO 2 stations Flux residuals exceed 1 GtC/yr in some zones Network is too sparse Inversion tests global X CO2 pseudo-data with 1 ppm accuracy flux errors reduced to <0.5 GtC/yr/zone for all zones Global flux error reduced by a factor of ~3. Flux Retrieval Error GtC/yr/zone

6. Welcome-6 OCO Mission First global, space-based observations of atmospheric CO 2 –high accuracy, resolution and coverage –geographic distribution of CO 2 sources and sinks and variability High resolution spectroscopic measurements of reflected sunlight – NIR CO 2 and O 2 bands Remote sensing retrieval algorithms –estimates of column-averaged CO 2 dry air mole fraction (X CO2 ) –accuracies near 0.3% (1 ppm) Chemical transport models –spatial distribution of CO 2 sources and sinks –two annual cycles

7. Welcome-7 Spectroscopy O 2 A band Clouds/Aerosols, Surface Pressure “strong” CO 2 band Clouds/Aerosols, H 2 O, Temperature “weak” CO 2 band Column CO 2 Column-integrated CO 2 abundance => Maximum contribution from surface High resolution spectroscopic measurements of reflected sunlight in near IR CO 2 and O 2 bands

8. Welcome-8 Retrieval Strategy

9. Welcome-9 Radiative Transfer Essentials Fundamental Equation of RT Beer’s Law Source Function (Emission, Scattering)

10. Welcome-10 Polarization and the Stokes Vector Electromagnetic radiation can be described in terms of the Stokes Vectors: I, Q, U & V –I - total intensity –Q & U - linear polarization –V - circular polarization Degree of Polarization (for OCO)

11. Welcome-11 Atmospheric and Surface Setup 11-layer plane-parallel atmosphere (4 in stratosphere) Urban, tropospheric and stratospheric aerosols Lambertian surface: albedos of 0.05, 0.1, 0.3 SZA: 10°, 40°, 70° VZA: 0°, 35°, 70° Azimuth: 0°, 45°, 90°, 135°, 180° Aerosol extinction optical depth: 0, 0.025, 0.25

12. Welcome-12 Extinction Processes

13. Welcome-13 Results for O 2 A Band with Rayleigh Scattering 0.0113 0.818 103.539

14. Welcome-14 Varying Solar Zenith Angle

15. Welcome-15 Varying Aerosol Loading

16. Welcome-16 Varying Surface Albedo

17. Welcome-17 Linear Sensitivity Analysis Park Falls, Wisconsin –Geometry Nadir viewing SZA: 75.1° (Jan), 34.8° (Jul) Azimuth: 210.9° (Jan), 240.0° (Jul) –Lorentzian ILS –Resolving Powers O 2 A Band: 17000 CO 2 Bands: 20000 –Errors July: 0.3 ppm January: 10 ppm

18. Welcome-18 Outlook Polarization: significant part of retrieval error budget Full vector retrieval too time-consuming and not practical Ways to handle polarization? –Orders of Scattering –Spectral Binning –Look-up tables