Simulation and retrieval for spaceborne aerosol and cloud high spectral resolution lidar of China

Clouds and aerosols can significantly affect global climate change and the atmospheric environment, and observing them three-dimensionally with high spatial and temporal resolutions is a long-standing issue. Spaceborne lidars are effective instruments for the vertical detection of clouds and aerosols globally. Numerous Mie scattering lidars were successfully launched and widely used, such as the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and Geoscience Laser Altimeter System. However, the retrieval of Mie scattering lidar data is an ill-posed problem that introduces a large uncertainty. The spaceborne Aerosol and Cloud High Spectral Resolution Lidar (ACHSRL) of China is currently under development and scheduled for launch in the near future. The ACHSRL attracted extensive attention, because it can separate Mie and Rayleigh scattering signals and avoid ill-posed retrieval. In this study, we conducted ACHSRL signal simulation and retrieval to explore the potential of the ACHSRL. First, we proposed a simplified scheme for retrieving optical parameters, which reduced the number of equations and intermediate variables of the traditional method and avoided false extrema in the backscatter coefficient retrieval. Additionally, the experiments showed that the backscatter coefficient retrieval was overestimated owing to the influence of the Poisson noise but can be corrected. Second, we examined the feasibility of the strategy of “first retrieving the lidar ratio then retrieving the extinction coefficient” to improve the extinction coefficient retrieval. We found that the retrieval error in the simulated cases can be reduced to less than 1% of the original retrieval error. Furthermore, we discussed the influence of the uncertainty of the iodine filter transmittance on the retrieval of the optical parameters and found that the average relative error was less than 1‰. Finally, we conducted simulation and retrieval based on the atmospheric parameters measured by the CALIOP. Results showed that the relative error in the backscatter and extinction coefficients at night was 12% and 28% for test cases, respectively, which was superior to that in the backscatter and extinction coefficients of the corresponding CALIOP product (i.e., 75% and 82%). This research is significant and useful for the development and application of satellite lidars in the future.