Atmospheric CO2 measurements with a 2μm airborne laser absorption spectrometer employing coherent detection

We report airborne measurements of CO2 column abundance conducted during two 2009 campaigns using a 2.05 mu m laser absorption spectrometer. The two flight campaigns took place in the California Mojave desert and in Oklahoma. The integrated path differential absorption (IPDA) method is used for the CO2 column mixing ratio retrievals. This instrument and the data analysis methodology provide insight into the capabilities of the IPDA method for both airborne measurements and future global-scale CO2 measurements from low Earth orbit pertinent to the NASA Active Sensing of CO2 Emissions over Nights, Days, and Seasons mission. The use of a favorable absorption line in the CO2 2 mu m band allows the on-line frequency to be displaced two (surface pressure) half-widths from line center, providing high sensitivity to the lower tropospheric CO2. The measurement repeatability and measurement precision are in good agreement with predicted estimates. We also report comparisons with airborne in situ measurements conducted during the Oklahoma campaign. (C) 2011 Optical Society of America