Abstract

The NASA Orbiting Carbon Observatory (OCO) will make space-based measurements of atmospheric CO2 with the precision, resolution, and coverage needed to characterize CO2 sources and sinks on regional scales and quantify their variability. OCO will be launched into the A-train end of 2008. The observatory carries a single instrument that incorporates three high-resolution grating spectrometers, designed to make bore-sighted measurements of the near-infrared absorption bands of CO2 and O2 in reflected sunlight. These measurements will be combined to estimate the column averaged CO2 dry air mole fraction, XCO2 . OCO is specially designed to be sensitive to near-surface CO2 concentrations and due to its nadir and sunglint modes will provide soundings over land and ocean. Here we will discuss the characteristics of OCO soundings and their measurement uncertainties, given by an analysis of the OCO forward model for different surface types, aerosol loadings, and solar zenith angle and we will assess merits of OCO ’s nadir- and glint-viewing modes. We will examine aerosol and cloud statistics derived from MODIS and other satellites to determine the spatio-temporal distribution of the OCO measurement errors and to obtained the expected number of cloud-free OCO soundings from which multi-shot measurement errors are calculated. Finally, we will discuss how well we expect OCO ’s column-CO2 measurements can constrain the surface sources and sinks. These investigations will provide important feedback to help isolate areas where the retrieval must be improved and give guidance on the optimal observation and sounding selection strategy for OCO .