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

Abstract

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.