The NASA Orbiting Carbon Observatory: Development Status

The Orbiting Carbon Observatory (OCO) will be launched into the Earth Observing System Afternoon Constellation (A-Train) in December 2008. This NASA Earth System Science Pathfinder (ESSP) mission will make spatially resolved measurements of the column-averaged CO2 dry air mole fraction, XCO2, over the sunlit hemisphere the Earth. These measurements will be analyzed with chemical tracer transport models to retrieve CO2 sources and sinks on regional scales and quantify their variability over the seasonal cycle. The observatory consists of a dedicated, 3-axis stabilized spacecraft bus that carries and points a single instrument. The instrument incorporates 3 bore sighted, high resolution grating spectrometers that will make coincident measurements of reflected sunlight in near-infrared CO2 and molecular oxygen (O2) bands. High spectral resolution (λ/Δλ>20,000) measurements within the CO2 absorption bands near 1.61 and 2.06 μm yield column abundance estimates that are most sensitive to the CO2 mixing ratios near the surface, where most sources and sinks are located. High resolution (λ/Δλ>17,000) measurements within the 0.765-μm O2 A-band spectra yield clear-sky surface pressure estimates with accuracies near 1 mbar over most of the sunlit hemisphere and constrain cloud and aerosol profiles to reduce uncertainties associated with multiple scattering. The instrument is currently being integrated and tested at the NASA Jet Propulsion Laboratory. Preliminary tests of the instrument focus indicate that all 3 spectrometers meet the stringent spectroscopic performance requirements needed to yield regional-scale XCO2 estimates with errors and systematic biases no larger than 0.3%.