Airborne measurement of atmospheric methane concentration using pulsed lidar

Abstract

We demonstrate the airborne measurement of atmospheric methane using a pulsed lidar at 1650 nm using an integrated path differential absorption scheme. Our seeded nanosecond-pulsed optical parametric amplifier (OPA)-based instrument works up to the highest altitudes flown (>10 km). Our airborne measurements are in good agreement with the expected atmospheric absorption. The difference between the measured absorption expressed in terms of the differential optical depth (DOD) and the predicted DOD calculated using Global Modeling and Assimilation Office (GMAO) data is 0.027±0.038 (standard deviation), with the DOD ranging from 0.5 to 2. For large sections of the flight, the measured absorption profile agrees within 2% rms of the predicted absorption profile. Overall, the retrieved atmospheric methane concentration lies within 11% of the true concentration, the latter estimated from our onboard in situ Picarro cavity ring down spectrometer.