Page 1 1 of 25, AGU Fall Meeting Dec Vijay Natraj (Caltech), Hartmut Bösch (Leicester), Rob Spurr (RT Solutions), Yuk Yung (Caltech) AGU Fall Meeting December 17, 2008 Glint and Target Mode Simulations for the Orbiting Carbon Observatory

Page 2 2 of 25, AGU Fall Meeting Dec Project and Mission Overview Salient Features: High-resolution, three-channel grating spectrometer Partnership with HS (Instrument) and OSC (Spacecraft) High heritage spacecraft, flies in formation with the A-Train Launch date: 15 January 2009 on Taurus XL from VAFB Operational life: 2 years Principal Investigator: Dr. David Crisp, Deputy: Dr. Charles Miller Project Manager: Thomas Livermore, Deputy: Dr. Ralph Basilio Earth Science Flight Projects Office Manager: Dr. Steven Bard, JPL ESSP Program Manager : Edward Grigsby, LaRC Program Scientist: Dr. William Emanuel, NASA HQ ESSP Program Executive: Eric Ianson, NASA HQ The Orbiting Carbon Observatory (OCO) Watching The Earth Breathe…Mapping CO 2 From Space Science: Collect the first space-based measurements of atmospheric CO 2 with the precision, resolution, and coverage needed to characterize its sources and sinks on regional scales and quantify their variability over the seasonal cycle. Use independent data validation approaches to ensure high accuracy (1-2 ppm, 0.3% - 0.5%) Reliable climate predictions require an improved understanding of CO 2 sinks What human and natural processes are controlling atmospheric CO 2 ? What are the relative roles of the oceans and land ecosystems in absorbing CO 2 ?

Page 3 3 of 25, AGU Fall Meeting Dec Mission System Description Mission Ops (OSC)NASA GN (GSFC) and SN (TDRSS) 3-channel Spectrometer (JPL/HS) Data Processing Center (JPL) Ground Validation Sites Taurus XL 3110 (KSC) Please visit for more informationhttp://oco.jpl.nasa.gov Dedicated Spacecraft (OSC)

Page 4 4 of 25, AGU Fall Meeting Dec OCO Glint Mode Glint Spot Ground Track  R  I Glint Observations: views “glint” spot Angle of reflection equals angle of incidence of sunlight at surface:  R =  I Improves SNR over oceans 70% time spent over oceans Spacecraft Coordinates Azimuth Orientation

Page 5 5 of 25, AGU Fall Meeting Dec OCO Target Mode Tracks a stationary surface target (calibration site) to collect large numbers of soundings Uplooking ground-based FTS data acquired simultaneously through same slant column Acquire Target data over 1 surface validation site each day 447-m WLEF Tower Geolocation Accuracy Scan Direction Spatial Direction Along Slit

Page 6 6 of 25, AGU Fall Meeting Dec Polarization Characteristics of OCO Spectrometers Transmits light with polarization parallel to slit I: intensity; Q, U: components of linear polarization; : angle between slit axis and principal plane (polarization angle) Nadir and glint modes: Target mode: measurement not restricted to principal plane

Page 7 7 of 25, AGU Fall Meeting Dec OS Model Schematic Scenario 1 Scenario 2 scatterer Scenario 3 scatterer Scenario 4 scatterer 1 scatterer 2 Natraj and Spurr, JQSRT, 107, 263–293, 2007

Page 8 8 of 25, AGU Fall Meeting Dec Glint Mode: Scenarios Solar Zenith Angle (SZA): 15°, 45°, 60°, 65°, 70°, 75° Aerosol Optical Thickness (AOT): 0 (Rayleigh), 0.01, 0.05, 0.1, 0.3 Dusty maritime aerosol (Kahn et al., JGR, 2001) Background stratospheric aerosol Ocean surface reflectance simulated using Cox-Munk model Wind Speed: 4 m/s, 8 m/s, 12 m/s

Page 9 9 of 25, AGU Fall Meeting Dec Spectral Residuals (Glint): Scalar Model Wind speed = 4 m/s Residual = Model-Exact(VLIDORT)

Page of 25, AGU Fall Meeting Dec Spectral Residuals (Glint): R-2OS Model Wind speed = 4 m/s Residuals from R-2OS model are smaller by 1–2 orders of magnitude

Page of 25, AGU Fall Meeting Dec Glint X CO2 Errors Scalar Model R-2OS Model X CO2 errors from R-2OS model < 1 ppm; scalar model errors as high as 5 ppm AOT ↑ Wind speed = 4 m/s

Page of 25, AGU Fall Meeting Dec Glint X CO2 and Surface Pressure Errors Retrieval error dominated by incorrect estimation of surface pressure; other effects become more important for large AOTs

Page of 25, AGU Fall Meeting Dec Glint X CO2 Errors Scalar Model R-2OS Model X CO2 errors larger when only O 2 A band contributes to forward model error => CO 2 and O 2 errors cancel out in the ratio

Page of 25, AGU Fall Meeting Dec Target Mode: Scenarios Location: Bremen (OCO validation site) Solar Zenith Angle (SZA): 50.4° Polarization angle: °, °, ° Scatterer scenarios: 0.05 AOT, 0.05 AOT+0.25 Cirrus OT, 0.3 AOT Surface: Lambertian

Page of 25, AGU Fall Meeting Dec Target X CO2 Errors Scalar Model R-2OS Model 0.05 AOT 0.05 AOT+0.25 Cirrus OT 0.3 AOT

Page of 25, AGU Fall Meeting Dec Target X CO2 Errors Scalar Model R-2OS Model X CO2 errors from R-2OS model < 1 ppm; scalar model errors as high as 30 ppm

Page of 25, AGU Fall Meeting Dec Summary Ignoring polarization could lead to significant (as high as 40 ppm) errors (that are much larger than the measurement noise) in X CO2 retrievals 2OS approach to account for polarization works very well (in and out of principal plane), giving X CO2 errors that are typically smaller than 1 ppm, and smaller or comparable to measurement noise Errors dominated by errors in retrieved surface pressure R-2OS model two orders of magnitude faster than a full vector calculation Model needs to be tested for glint over land

Page of 25, AGU Fall Meeting Dec Backup Slides

Page of 25, AGU Fall Meeting Dec RT Model Scalar multiple scattering model: Radiant (R) –Discrete ordinate solution for layer reflection and transmission matrices –Adding method to obtain combined matrices for different layers –Linearized: derivatives of intensity w.r.t. optical depth and single scattering albedo obtained analytically Polarization: 2OS –Polarization approximated by two orders of scattering –Analytic integration over optical depth –Fast invariant imbedding approach to add individual layers –Linearized

Page of 25, AGU Fall Meeting Dec Radiance Results: Clear Sky SZA ↑ Glint reflectance ~ 10 times larger at 75° than at 15° Wind speed = 4 m/s

Page of 25, AGU Fall Meeting Dec Radiance Results: Cloudy Sky (AOT = 0.3) Wind speed = 4 m/s Q decreases! For large SZA, slant-path attenuation of solar beam very large; large fraction of light comes from atmospheric scattering

Page of 25, AGU Fall Meeting Dec Linear Error Analysis Forward model errors systematic Bias in retrieved parameters x Bias can be expressed as follows: G: gain matrix –Describes mapping of measurement variations into retrieved vector variations ΔF: forward model error

Page of 25, AGU Fall Meeting Dec Glint X CO2 Errors Scalar Model R-2OS Model X CO2 errors from R-2OS model < 1 ppm; scalar model errors as high as 5 ppm AOT ↑ Wind speed = 4 m/s Wind speed = 8 m/s Wind speed = 12 m/s

Page of 25, AGU Fall Meeting Dec Glint X CO2 and Surface Pressure Errors Retrieval error dominated by incorrect estimation of surface pressure; other effects become more important for large AOTs Wind speed = 4 m/s Wind speed = 8 m/s Wind speed = 12 m/s

Page of 25, AGU Fall Meeting Dec Glint X CO2 Errors Scalar Model R-2OS Model Wind speed = 4 m/s Wind speed = 8 m/s Wind speed = 12 m/s X CO2 errors larger when only O 2 A band contributes to forward model error => CO 2 and O 2 errors cancel out in the ratio