Although the empirical mode decomposition (EMD) method is an effective tool for noise reduction in lidar signals, evaluating the effectiveness of the denoising method is difficult. A dual-field-of-view lidar for observing atmospheric aerosols is described. The backscattering signals obtained from two channels have different signal-to-noise ratios (SNRs). The performance of noise reduction can be investigated by comparing the high SNR signal and the denoised low SNR signal without a simulation experiment. With this approach, the signal and noise are extracted to one intrinsic mode function (IMF) by the EMD- based denoising; thus, the threshold method is applied to the IMFs. Experimental results show that the improved threshold method can effectively perform noise reduction while preserving useful sudden-change information.
The profiles of aerosol extinction,backscatter coefficient,and lidar ratio in the lower troposphere over Wuhan are measured by a multi-channel Raman/Mie lidar.Using the lidar ratio retrieved by Raman scattering principle,the profiles of aerosol extinction and backscatter coefficients are also retrieved by Mie scattering signals,without a prior assumption about their relation in the traditional pure Mie signals data analyses.The observations by both Raman and Mie are in good agreement with each other.The high coherence shows that the system is reliable,and the Mie and Raman channels are in good adjustment and have the same field of view.
