The Orbiting Carbon Observatory OCO Mission http oco

The Orbiting Carbon Observatory (OCO) Mission http: //oco. jpl. nasa. gov Vijay Natraj (Caltech) Ge 152 May 28 2008 1 of 14, Vijay, Ge 152 Page 1

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? 2 of 14, Vijay, Ge 152 Page 2

Why Measure CO 2 from Space? Studies from GV-CO 2 stations – – Flux residuals exceed 1 Gt. C/yr in some zones Network is too sparse 0. 6 0. 0 Inversion tests – – – 1. 2 Global XCO 2 pseudo-data with 1 ppm accuracy Flux errors reduced to < 0. 5 Gt. C/yr/zone for all zones Global flux error reduced by a factor of ~3 0. 6 0. 0 Courtesy: Rayner and O’Brien, 2001 3 of 14, Vijay, Ge 152 Page 3 Flux Residuals (Gt/yr/zone) • 1. 2

CO 2 Mixing Ratio (ppm) Precise CO 2 Measurements Needed • Space-based XCO 2 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 4 of 14, Vijay, Ge 152 Page 4

The Orbiting Carbon Observatory (OCO) 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. • Spectra of CO 2 and O 2 absorption in reflected sunlight used to estimate XCO 2 • Random errors and biases no larger than 1 2 ppm (0. 3 - 0. 5%) on regional scales at monthly intervals 5 of 14, Vijay, Ge 152 Page 5

OCO Fills a Critical Measurement Gap 6 NOAA TOVS CO 2 Error (ppm) 5 Aqua AIRS 4 ENVISAT SCIAMACHY 3 2 Aircraft Flask Site 1 0 1 OCO Flux Tower Globalview Network 10000 100 Spatial Scale (km) OCO will make precise global measurements of XCO 2 needed to monitor CO 2 fluxes on regional to continental scales. 10 6 of 14, Vijay, Ge 152 Page 6

Spectroscopy • Column-integrated CO 2 abundance – Maximum contribution from surface • Why high spectral resolution? – Enhances sensitivity, minimizes biases CO 2 2. 06 m O 2 A-band CO 2 1. 61 m Clouds/Aerosols, Surface Pressure 7 of 14, Vijay, Ge 152 Column CO 2 Clouds/Aerosols, H 2 O, Temperature Page 7

OCO Will Fly in the A-Train Coordinated Observations GLORY 1: 34 1: 26 OCO files at the head of the A-Train, 4 minutes ahead of the Aqua platform 8 of 14, Vijay, Ge 152 Page 8

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 9 of 14, Vijay, Ge 152 Page 9

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 R I Glint Spot ck a r d. T n u Gro Local Nadir More interference from clouds Operations more complicated 10 of 14, Vijay, Ge 152 Page 10

Target Observations • 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 • Tracks a stationary surface target (calibration site) to collect large numbers of soundings Scan Direction 11 of 14, Vijay, Ge 152 Spa tial Alo Directi ng S on lit Geolocation Accuracy Page 11

Retrieval Algorithm 12 of 14, Vijay, Ge 152 Page 12

Validation Program • Ground-based in-situ measurements • NOAA CMDL Flask Network + Tower Data • TAO/Taurus Buoy Array • Uplooking FTS measurements of XCO 2 • 3 funded by OCO • 4 upgraded NDSC • Aircraft measurements of CO 2 profile Buoy Network 13 of 14, Vijay, Ge 152 CMDL Page 13

Acknowledgments • Yuk Yung • David Crisp, Charles Miller • Retrieval Algorithm: Denis O’Brien, Geoff Toon, Bhaswar Sen, Hartmut Boesch, Rob Spurr, Hari Nair, James Mc. Duffie, Mick Christi • Validation: Paul Wennberg, Ross Salawitch, Brian Connor • Calibration: Carol Bruegge • OCO Science Team 14 of 14, Vijay, Ge 152 Page 14