Airborne Laser Absorption Spectrometer Measurements of Atmospheric CO sub(2) Column Mole Fractions: Source and Sink Detection and Environmental Impacts on Retrievals

This paper provides atmospheric CO2 column abundance measurement results from a summer 2011 series of flights of a 2.05-m laser absorption spectrometer on the NASA DC-8 research aircraft. The integrated path differential absorption (IPDA) method is used for the CO2 column mole fraction retrievals. This instrument and the data analysis methodology developed to achieve retrievals over complex terrain and variable atmospheric conditions 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 proposed NASA Active Sensing of CO2 Emissions over Nights, Days, and Seasons (ASCENDS) mission. Demonstrated in this paper is the capability to measure CO2 drawdown caused by crop activity during a midday flight over the U.S. upper Midwest area. In addition, an example is provided of high spatial resolution measurements of CO2 plumes from individual stack clusters of the Four Corners Power Plant in northwestern New Mexico. Complex terrain, the spectral properties of the aboveground scatterers, and potential cloud contamination are factors that complicate the column abundance retrieval. The impacts of these factors and various means of minimizing these influences in the retrievals are discussed.