Page 1 1 of 14, Vijay, Ge152 The Orbiting Carbon Observatory(OCO) Mission The Orbiting Carbon Observatory (OCO) Mission Vijay Natraj (Caltech) Ge152 May

Page 2 2 of 14, Vijay, Ge152 Introduction: Carbon Sinks? Atmospheric Carbon dioxide (CO 2 ) –Primary man-made greenhouse gas –Mixing ratios increased by ~25% since 1860 –Only half of the CO 2 from fossil fuel emissions in atmosphere Outstanding Issues –Where are the CO 2 sinks? –Why does atmospheric buildup vary with uniform emission rates? –How will CO 2 sinks respond to climate change?

Page 3 3 of 14, Vijay, Ge152 Why Measure CO 2 from Space? Studies from 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 Courtesy: Rayner and O’Brien, Flux Residuals (Gt/yr/zone) Flux Residuals (Gt/yr/zone)

Page 4 4 of 14, Vijay, Ge152 Precise CO 2 Measurements Needed Space-based X CO2 estimates will improve constraints on CO 2 fluxes –Near global coverage on monthly intervals –Precisions of 1–2 ppm (0.3–0.5%) on regional scales –No spatially coherent biases > 1–2 ppm (0.3 to 0.5%) on regional scales CO 2 Mixing Ratio (ppm) Latitude Latitude

Page 5 5 of 14, Vijay, Ge152 The Orbiting Carbon Observatory (OCO) Spectra of CO 2 and O 2 absorption in reflected sunlight used to estimate X CO2 Random errors and biases no larger than ppm ( %) on regional scales at monthly intervals OCO will make the first space-based measurements with the precision and resolutions needed to quantify CO 2 sources and sinks and monitor their variability.

Page 6 6 of 14, Vijay, Ge152 OCO Fills a Critical Measurement Gap OCO will make precise global measurements of X CO2 needed to monitor CO 2 fluxes on regional to continental scales. Spatial Scale (km) CO 2 Error (ppm) OCO Flask Site Aqua AIRS Aircraft 0 Flux Tower Globalview Network NOAA TOVS ENVISAT SCIAMACHY

Page 7 7 of 14, Vijay, Ge152 Spectroscopy Clouds/Aerosols, Surface PressureClouds/Aerosols, H 2 O, TemperatureColumn CO 2 Column-integrated CO 2 abundance –Maximum contribution from surface Why high spectral resolution? –Enhances sensitivity, minimizes biases O 2 A-band CO  m CO  m

Page 8 8 of 14, Vijay, Ge152 OCO Will Fly in the A-Train OCO files at the head of the A-Train, 4 minutes ahead of the Aqua platform 1:26 Coordinated Observations GLORY 1:34

Page 9 9 of 14, Vijay, Ge152 Nadir Observations Observatory points instrument at local nadir –Collects science data over sunlit hemisphere at solar zenith angles < 85  Advantages + Small footprint (< 3 km 2 ) isolates cloud-free scenes and reduces biases from spatial inhomogeneities over land + Simplifies operations Liabilities  Low Signal/Noise over dark ocean

Page of 14, Vijay, Ge152 Glint Observations Glint Observations: views “glint” spot –Angle of reflection equals angle of incidence of sunlight at surface:  R =  I Advantages + Improves Signal/Noise over oceans Disadvantages  More interference from clouds  Operations more complicated Local Nadir Glint Spot Ground Track  R  I

Page of 14, Vijay, Ge152 Target Observations 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 of 14, Vijay, Ge152 Retrieval Algorithm

Page of 14, Vijay, Ge152 Validation Program Ground-based in-situ measurements NOAA CMDL Flask Network + Tower Data TAO/Taurus Buoy Array Uplooking FTS measurements of X CO2 3 funded by OCO 4 upgraded NDSC Aircraft measurements of CO 2 profile Buoy Network CMDL

Page of 14, Vijay, Ge152 Acknowledgments Yuk Yung David Crisp, Charles Miller Retrieval Algorithm: Denis O’Brien, Geoff Toon, Bhaswar Sen, Hartmut Boesch, Rob Spurr, Hari Nair, James McDuffie, Mick Christi Validation: Paul Wennberg, Ross Salawitch, Brian Connor Calibration: Carol Bruegge OCO Science Team