4:45 PM - 5:00 PM
[ACG41-06] An Iteration Algorithm of Aerosol Composition and Optical Property Retrieval from Dual-Wavelength Mie Lidar Observations
Keywords:Aerosol retrieval, Mie Lidar, Dual-wavelength, Aerosol extinction coefficient, Lidar ratio
Mie lidar has been profoundly applied in the retrieval of aerosol optical coefficients. However, few studies further explore the strategies to retrieve aerosol mass profiles quantitively from lidar observation. An iteration algorithm for profiling aerosol mass composition as well as extinction coefficients from spaceborne dual-wavelength lidar data is proposed. By constructing the relationship between optical properties and mass profiles of mixed aerosols at different wavelengths, constraints in channels are induced to improve the accuracy of lidar ratio, which is essential for the retrieval of aerosol extinction coefficients. First, the initial guess of aerosol composition and the aerosol mass profiles are estimated based on an a prior information from analyzing the historical monthly mean aerosol profiles in local region. The corresponding Lidar ratio and optical properties at dual-channels are calculated according to the complex refractive index of mixed aerosols and Mie theory by a forward model. Second, by applying the Lidar ratios in the Fernald retrieval method, aerosol extinction coefficients are obtained from the lidar observation. Then, combining the model constructed between aerosol extinctions coefficients and aerosol mass profiles at layers by Mie theory, the aerosol mass profiles can be deduced. Comparing the differences of the aerosol mass profiles at dual channels and the aerosol extinctions coefficients from retrieval and forward route, the initial guess of aerosol mass profile, aerosol composition and its corresponding Lidar ratio are modified. Finally, optimal aerosol extinction profiles are gained from the iteration of the above steps.
The feasibility and practicality of this technique is analyzed by applying in both simulated space-borne lidar backscatter signals and CALIOP data. Compared with the retrieval results from the method based on the empirical estimated lidar ratio, the proposed method yields mean accuracy improvement of extinction coefficient at 532 nm and 1064 nm channels by 19.70% and 3.41%, and column mass of dust and sulfate aerosol by 12.90% and 20.73%, respectively. The results retrieved from CALIOP data also confirm the feasibility of the method for the on-board data application. By applying the method in the simulated data from the aerosol profiles with wide range of AOD value and different mixing ratios, the paper further evaluates the robustness of the proposed method. It reveals that the method yields better improved accuracy of the extinction coefficient retrieval rather than the method with empirical estimated lidar ratio, especially for the profiles with high AOD value. The inherent behavior of the method in aerosol mass composition profiling is also discussed. Both the aerosol extinction coefficient accuracy and the proportion of the aerosols affect the retrieval accuracy. The accuracy of aerosol extinction coefficient directly impacts on the retrieval of aerosol mass profiles owing to the connection constructed in the proposed method by the lidar ratio. And competition can be observed in the mass composition retrieval accuracy between the two aerosol types. The enhancement of accuracy is much obvious for the aerosol which yield higher proportion.
The feasibility and practicality of this technique is analyzed by applying in both simulated space-borne lidar backscatter signals and CALIOP data. Compared with the retrieval results from the method based on the empirical estimated lidar ratio, the proposed method yields mean accuracy improvement of extinction coefficient at 532 nm and 1064 nm channels by 19.70% and 3.41%, and column mass of dust and sulfate aerosol by 12.90% and 20.73%, respectively. The results retrieved from CALIOP data also confirm the feasibility of the method for the on-board data application. By applying the method in the simulated data from the aerosol profiles with wide range of AOD value and different mixing ratios, the paper further evaluates the robustness of the proposed method. It reveals that the method yields better improved accuracy of the extinction coefficient retrieval rather than the method with empirical estimated lidar ratio, especially for the profiles with high AOD value. The inherent behavior of the method in aerosol mass composition profiling is also discussed. Both the aerosol extinction coefficient accuracy and the proportion of the aerosols affect the retrieval accuracy. The accuracy of aerosol extinction coefficient directly impacts on the retrieval of aerosol mass profiles owing to the connection constructed in the proposed method by the lidar ratio. And competition can be observed in the mass composition retrieval accuracy between the two aerosol types. The enhancement of accuracy is much obvious for the aerosol which yield higher proportion.