Study on Influences of Atmospheric Factors on Vertical Profile Retrieving From Ground-Based DIAL at 1.6 μm

Differential absorption lidar (DIAL) is widely accepted as the most promising remote sensing means to map the global CO₂ concentrations. Nevertheless, diurnal variations and vertical distributions of atmospheric CO₂ cannot be obtained by satellite-borne and airborne measurements. Ground-based DIAL systems are developed to fill this gap, as well as serve as validations for satellite-borne measurements. Atmospheric factors play significant roles in obtaining accurate range-resolved measurements of XCO₂. However, the influence of atmospheric factors on the performance of a ground-based DIAL system aiming at CO₂ measurements has not been dedicatedly discussed yet. The pressure, temperature, and water vapor of the atmosphere have been taken into consideration for performance evaluation after preselection of absorption lines around 1.6 μm in this paper. In addition, errors caused by variations of aerosols have also been analyzed by using theoretical simulations and real measurements. We found that biases caused by temperature and pressure uncertainties were 0.11-0.45 ppm/K and 0.39 ppm/hPa, respectively, if the central wavelength was utilized as the online wavelength. In addition, the water vapor effect could be neglected by cautious selection of online and offline wavelength. Finally, if the online and offline wavelengths were transmitted alternatively, the temporal and range resolutions have to be determined very carefully to balance the signal-to-noise ratio of acquired data and tolerable errors derived from variations of aerosols. A variable range resolution is recommended for CO₂ measurements at different altitudes to fulfill the target precision.