Airborne Lidar Measurements of Atmospheric CO₂ Column Concentrations to Cloud Tops made during the 2017 ASCENDS/ABoVE Campaign

Abstract. We measured the column-averaged atmospheric CO₂ mixing ratio (XCO₂) to a variety of cloud tops with an airborne pulsed multi-wavelength integrated path differential absorption (IPDA) lidar during NASA’s 2017 ASCENDS/ABoVE field campaign. Measurements of height- resolved atmospheric backscatter profiles allow this lidar technique to estimate XCO₂ to cloud tops as well as to the ground with accurate knowledge of the photon path-length. We validated these measurements with those from an onboard in situ CO₂ sensor during spiral down maneuvers. These lidar measurements were 2–3 times better than those from previous airborne campaigns, due to our using a wavelength step-locked laser diode source and a high-efficiency detector for this campaign. Precisions of 0.6 parts per million (ppm) were achieved for 10-s average measurements to mid-level clouds and 0.9 ppm to low-level clouds at the top of the planetary boundary layer. This study demonstrates the lidar’s capability to fill in XCO₂ measurement gaps in cloudy regions and to help resolve the vertical and horizontal distributions of atmospheric CO₂. Future airborne campaigns and spaceborne missions with this capability can be used to improve atmospheric transport modeling, flux estimation, and carbon data assimilation.