Impact of Using Assimilated Data for Evaluating Performance of Active CO2 Optical Depth Measurements

Abstract:

NASA has recently conducted multiple DC-8 flight campaigns of candidate instruments for the future Active Sensing of CO₂ Emissions over Nights, Days, and Seasons (ASCENDS) mission. For each campaign, the precision and accuracy of the remote measurements of atmospheric CO₂ differential absorption optical depths from the candidate instruments were evaluated with respect to corresponding modeled CO₂ optical depths derived from in situ profiles of atmospheric state variables including atmospheric CO₂ mixing ratios, temperature (T), pressure (p), and humidity (q) and using the HITRAN spectroscopic database. To enable this evaluation, the DC-8 flights were designed to include multiple overpasses of a comparison location where the aircraft performed a spiral ascent or descent and captured the in situ profiles using a suite of onboard instruments. However large segments of some flights took place far from spiral locations and therefore had no coincident in situ measurements of the atmospheric state (CO₂, T, p, q). For these situations meterological analysis data from the Goddard Modeling and Assimilation Office (GMAO) GEOS-5 gridded data have been used to assimilate atmospheric state profiles for use in the CO₂ optical depth derivation. We use the location of the DC-8 spirals to identify all of the GMAO GEOS-5 gridded profiles that would compare with each spiral and report their differences with respect to the DC-8 in situ profiles. We show how these differences affect the modeled CO₂ optical depth for the three campaigns and the impacts of these differences on the precision and accuracy evaluations of the remote CO₂ measurements.