Analysis of Range Measurements From a Pulsed Airborne CO2 Integrated Path Differential Absorption Lidar

Determining the CO2 column abundance from an integrated path differential absorption (IPDA) lidar requires accurate knowledge of the range to the scattering surface, i.e., the column height. We have adapted and tested a ranging algorithm for the airborne IPDA CO2 lidar designed at the NASA Goddard Space Flight Center, and have evaluated its accuracy and precision. We applied a quasi-maximum-likelihood method, using cross correlation, to estimate the range from the lidar's 1-mu s-wide echo pulses. The objective was to show that the use of these temporally long laser pulses allows the determination of the optical path length with required precision. We analyzed airborne measurements made in August 2009 over the Chesapeake Bay near the Eastern Shore of Virginia. The results indicate a ranging precision of better than 3 m, which is sufficient for airborne and space-based retrievals of CO2 column concentration.