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 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 radiative transfer calculations using the HITRAN spectroscopic database in combination with recent measurements of spectral line parameters. 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 in situ derived CO₂ optical depth for the three campaigns and the impacts of these differences on the precision and accuracy evaluations of the remote CO₂ measurements.