Monitoring CO2 Sources and Sinks from Space with the Orbiting Carbon Observatory (OCO)

The NASA Earth System Science Pathfinder (ESSP) Orbiting Carbon Observatory (OCO) is currently scheduled for launch in late 2008. During its 2 year nominal mission, this satellite will acquire spatially resolved measurements of the column averaged atmospheric CO2 dry air mole fraction, (XCO2) with the precision, resolution, and coverage needed to characterize the geographic distribution of CO2 sources and sinks and quantify their variability over the seasonal cycle. The observatory carries a single instrument designed to measure the absorption of reflected sunlight by CO2 and molecular oxygen (O2) at near infrared wavelengths. Bore-sighted spectroscopic measurements the CO2 and O2 column abundance will be analyzed to retrieve spatial variations in XCO2. OCO will fly in the Earth Observing System Afternoon Constellation (A-Train). This circular, 705 km altitude, near-polar, sun synchronous orbit that provides global coverage of the sunlit hemisphere with a 16-day ground-track repeat cycle. The instrument collects 12 to 24 soundings/second, yielding 200 to 400 samples per degree of latitude as it moves along it orbit track on the day side of the Earth. This provides 7 and 14 million soundings over the globe once every 16 days. Clouds, aerosols, and other factors will reduce the number of soundings available for XCO2 retrievals, but existing studies suggest that between 10 to 20% of these data will be sufficiently cloud free to yield XCO2 estimates with accuracies of 0.3 to 0.5% (1 to 2 ppm) on regional scales at monthly intervals. A comprehensive ground-based validation network is being implemented to ensure that measurements meet these requirements. These measurements are expected to improve our understanding of the nature and processes that regulate atmospheric CO2 enabling more reliable forecasts of its buildup and its impact on climate change.