Random-modulation differential absorption lidar based on semiconductor lasers and single photon counting for atmospheric CO2 sensing

Abstract

Carbon dioxide (CO2) is the major anthropogenic greenhouse gas contributing to global warming and climate change. Its concentration has recently reached the 400-ppm mark, representing a more than 40 % increase with respect to its level prior to the industrial revolution. However, the exchanges of CO2 between the atmosphere and the natural or anthropogenic sources/sinks at the Earth’s surface are still poorly quantified. A better understanding of these surface fluxes is required for appropriate policy making. At present, the concentrations of CO2 are mainly measured in-situ at a number of surface stations that are unevenly distributed over the planet. Air-borne and spaceborne missions have the potential to provide a denser and better distributed set of observations to complement this network. In addition to passive measurement techniques, the integrated path differential absorption (IPDA) lidar technique [1] has been found to be potentially suited for fulfilling the stringent observational requirements. It uses strong CO2 absorption lines in the 1.57 or in the 2 μm region and the backscatter from the ground or a cloud top to measure the column averaged CO2 mixing ratio (XCO2) with high precision and accuracy. The European Space Agency (ESA), has studied this concept in the frame of the Advanced Space Carbon and Climate Observation of Planet Earth (A-SCOPE) mission in 2006. Although a lack of technological readiness prevented its selection for implementation, recommendations have been formulated to mature the instrument concept by pursuing technological efforts [2]. During the last years, a tremendous effort in the assessment of the optimal CO2 active sensing methodology is being performed in the context of NASA mission Active Sensing of CO2 Emissions over Nights, Days, and Season (ASCENDS