Data density, both in time and space, remains a primary limit to our ability to derive regional terrestrial CO₂ fluxes. Vertical differences in the CO₂ mixing ratio profile can be large, especially between the atmospheric boundary layer (ABL) and the free troposphere. Mixing between the ABL and the free troposphere is periodically vigorous (e.g. fronts, cloud convection) and can have a strong impact on the ABL CO₂ budget. Data from a continuous monitoring tropospheric CO₂ mixing ratio profiling system and the continental CO₂ mixing ratio measurement network that is being implemented in North America could be used to obtain daily to monthly net ecosystem-atmosphere exchange (NEE).

Active remote sensing capability for continuous CO₂ profiling in the atmosphere has already been demonstrated at NASA Langley Research Center using the Differential Absorption Lidar (DIAL) technique in the 2-micron region. This followed the development of high power, pulsed, narrow bandwidth, tunable lasers with the ability to lock onto optimum absorption lines for the measurement of CO₂ profiles. We plan to enhance the capability of the existing CO₂ DIAL system to enable improved tropospheric profiling of CO₂. The measurement precision of the system will be enhanced using recently acquired high quantum efficiency, high-gain, and low-noise detectors and a large collection area telescope. We plan to integrate the ground-based DIAL system and evaluate and optimize its performance. Well-calibrated, in situ infrared gas analyzers will be used to evaluate the DIAL system. We anticipate that the DIAL system will achieve 1% (3 ppm) absolute accuracy and 0.5% (1.5 ppm) precision while measuring CO₂ mixing ratios with 1 km vertical resolution and 30 minute temporal resolution up to range of 4 to 5 km. This precision will readily resolve the daily ABL – free troposphere mixing ratio difference.