The Application of EMD-CIIT Lidar Signal Denoising Method in Aerosol Detection

Abstract Integration of lidar inversion is generally carried out in the more stable backward, from a reference altitude down to the ground, rather than the forward direction. Small fluctuation of the signal at such altitude may lead to unacceptable deviation in the inversion results, so lidar signal denoising is required ahead of the inversion procedure. Empirical mode decomposition (EMD) method has been applied to signal denoising and the clear first interval thresholded empirical mode decomposition (EMD-CIIT) method performs well in lidar noise reduction. The micro pulse lidar CE 370-2 data is used to illustrate the efficiency of the EMD-CIIT denoising method by comparing with the wavelet method. EMD-CIIT method shows significant advantages at lower, higher altitudes and the cloud layer of the lidar profile. These two methods have similar performance at the middle part of the lidar profile. EMD-CIIT method preserves useful sudden-change atmospheric features and reduces noise meanwhile. There is an obvious diurnal variation of the lidar data quality: higher during the night and lower during the day. The signal to noise ratio (SNR) of the EMD-CIIT denoised data is 30.56 ± 4.73 for the whole day, 27.59 ± 3.47 during the night and 35.25 ± 1.68 during the day. The reference altitude of lidar inversion should be set to about 12 km. It should not be higher than 11.5 km during the day; however, it has a maximum of 15 km during the night.