An Optimal-Estimation based hybrid Rayleigh-Mie Extinction and Backscatter retrieval Method for HSRL lidars

The Rayleigh signal from a High-Spectral Resolution Lidar (HSRL) can be used to estimate the extinction profile in a rather direct manner by estimating the derivative of the range-corrected logarithmic signal. However, the applicability of this method is limited due to the high SNR required. Thus, one can assert that accurate but low-precision extinction information is, in general, provided by the Rayleigh signal. In contrast, extinction information can also be extracted from the Mie signal channel which, in general, may be viewed as less accurate (since factors such as the extinction-to-backscatter ratio must be assumed) but more precise (since the sensitivity to the SNR ratio of the input data is much lower). Taking into account these two observations, it is useful to construct a retrieval procedure which simultaneously uses both the Rayleigh and Mie signals in order to optimally combine the Rayleigh channel derived information with the less-accurate but more precise information derived using the Mie channel. To this end, an optimal-estimation based variational approach has been developed for the retrieval of lidar extinction and backscatter. In this presentation, the retrieval algorithm will be introduced and its application and performance demonstrated using synthetic data from the EarthCARE simulator for a variety of cloud and aerosol conditions