The NASA Goddard CO2 Sounder Lidar: 2017 Airborne Campaign as a Demonstration toward a Future Space Mission

NASA Goddard Space Flight Center has developed an integrated-path, differential absorption (IPDA) lidar approach to measure atmospheric column-averaged CO
2
mole fraction (XCO
2
). This pulsed laser approach uses a step-locked laser diode source, a fiber laser amplifier, and a high-sensitivity detector. The approach allows measurements of CO
2
absorption and time-resolved laser backscatter profiles. These enable accurate estimates of XCO
2
and range to the Earth's surface and cloud tops under a wide variety of conditions, including darkness, at low sun angles, through broken cloud fields, and the presence of aerosols. The CO
2
Sounder lidar team has demonstrated airborne measurements during several campaigns over the past decade. Here we use the data from the summer 2017 airborne campaign in Alaska to further demonstrate the capabilities of this technique. We validated the XCO
2
retrievals from the lidar against in situ measurements made from the aircraft during spiral-down maneuvers. The results show that this lidar approach provides XCO
2
measurements with low bias and high precision under a wide variety of measurement conditions. The campaign showed the lidar's capability to resolve the vertical and horizontal gradients of CO
2
and to quantify CO
2
enhancements from wildfires. The results show it is an attractive candidate for future airborne science campaigns and, with more laser power, for a space mission like NASA's planned Active Sensing of CO
2
Emissions over Nights, Days and Seasons (ASCENDS) mission.