Impacts of atmospheric state uncertainty on O₂ measurement requirements for the ASCENDS mission

Abstract. Remotely sensed observations of atmospheric composition require an estimate of surface pressure. This estimate can either come from an instrument with sensitivity in an O₂ absorption feature in the spectrum, or it can be provided by a numerical weather prediction (NWP) model. In this work, the authors outline an information-based methodology for setting measurement requirements for an active lidar measurement of O₂ in the context of the Active Sensing of Carbon Emissions over Nights, Days and Seasons (ASCENDS) mission. The results indicate that the impacts of correlations in the environmentally induced vertical weighting function errors between CO₂ and O₂ measurements are nontrivial and that the choice of CO₂ and O₂ wavelengths can lead to a stricter or looser requirement than that of surface pressure considerations alone, which would indicate about a 0.1 % precision for 1mb accuracy. Furthermore, the less sensitive the CO₂ measurement is to surface pressure errors, the more difficult it will be for an O₂ observation to provide a useful measurement.