Lidar measurements of CO2 column concentrations in the Arctic region of North America from the ASCENDS 2017 airborne campaign

Abstract

NASA Goddard’s CO2 Sounder is a pulsed, multiple-wavelength, IPDA-lidar. It was flown onboard the NASA DC-8 to measure atmospheric CO2 column concentrations (XCO2) in the lower stratosphere and troposphere of the Arctic region of North America as part of the 2017 ASCENDS airborne campaign. Eight flights covering 40,000 km were flown in late July and August over Alaska and Canada’s Northwest Territories, including a northern transit east of the Rockies and a return transit partly over the ocean between Alaska and California. The Arctic flights were coordinated with the 2017 Arctic-Boreal Vulnerability Experiment (ABoVE) campaign. The metrological conditions were challenging: a non-uniform CO2 distribution, a dynamic atmosphere and varied surface-reflectivity. To assess the accuracy of our lidar the aircraft’s scientific payload included the AVOCET and Picarro instruments. These two instruments measured in-situ XCO2 during the flights and column XCO2 from 47 separate descent spirals from ~12 km altitude to near ground at local airfields distributed throughout the measurement region. Each spiral maneuver allows a direct comparison between the retrievals of XCO2 from the lidar against those computed from insitu instruments. The CO2 Sounder worked very well during all phases of the campaign. Analysis to date shows the lidar measured column concentrations are in close agreement with in-situ column measurements with a precision of better than 0.8 ppm with 1 second averaging. In addition, preliminary analyses of measurements to the ubiquitous cloud tops also produced column concentrations and information on the vertical XCO2 structure.