Articles | Volume 8, issue 7
Research article
03 Jul 2015
Research article |  | 03 Jul 2015

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

S. Crowell, P. Rayner, S. Zaccheo, and B. Moore

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.

Short summary
We derive a yes/no requirement for the usefulness of an O2 lidar as part of the ASCENDS mission that incorporates errors due to atmospheric state misspecification as well as instrumental noise. We find that the larger the CO2 instrument's sensitivity to surface pressure errors, the lower the precision requirement for the O2 instrument to be useful. In particular, the 2um CO2 instrument would benefit the most from the inclusion of an O2 lidar with high precision retrievals of surface pressure.