Geometric Form Factor Retrieval Method for Ground-Based Lidar Based on Ground-Based and Space-Borne Synchronous Observation Data

To effectively retrieve the geometric form factor of the ground-based lidar and to modify the echoed signal in transition region, a new geometric form factor retrieval method is proposed. The method takes advantage of the characteristic of space-borne lidar (Cloud Aerosol Lidar Infrared Pathfinder Satellite Observation, CALIPSO) that it can cover the detection transition area of the ground-based lidar. The geometric form factors in off-axial and coaxial modes are determined by the use of simultaneous lidar measurement data from the space-borne lidar and the ground-based lidar. The results are compared to the results of comprehensive Raman-Mie method and Su Jia's method. In the transition region of the geometric form factor, the average relative errors of the aerosol backscatter coefficient can be improved by 25.4% and 10.4% compared to those of Su Jia's method in off-axial and coaxial modes, respectively. This method overcomes the uncertainties caused by assumptive uniformity of the atmosphere in the horizontal measurement method of the elastic scattering lidar. It is more suitable for the widely-used elastic scattering lidar. The geometric form factor of the ground-based lidar can be routinely calibrated by use of the regular transit time of CALIPSO with stable features.