Remote sensing of gaseous SF6 plume in troposphere using CO2 laser based DIAL according to ringing effect compensation

Abstract

A TEA-CO2 laser based DIAL is employed to determine the range resolved hexafluoride (SF6) concentration. An algorithm is developed here in favor of the lidar signal processing to improve the data assessment against the undesired ringing effect. The latter is known as a lidar waveform defect that arises from multiple reflections of transmission line during the data acquisition, detection and recording. Before retrieval of SF6 parameters, namely concentration and extinction coefficient, the noise removal is initially carried out by means of the wavelet thresholding. Then, the ringing effect is significantly suppressed according to the developed Gaussian decomposition method. Furthermore, the plume concentration is measured regarding the signal processing of the neighboring lines of the 32SF6 absorption band within the spectral range of 10.247–10.6 µm. The 32SF6 concentration is determined by improving the accuracy of the signal processing. The 3D visualization of the SF6 diffusion is carried out in time and distance domains through the lower troposphere too. Horizontal atmospheric extinction profiles are successively obtained based on the near boundary method (NBM) with the spatial resolution 3.75 m. Moreover, the extinction profiles are recorded in three typical meteorological conditions i.e. 2 × 10−4 m−1 (morning-still), 6 × 10−4 m−1 (afternoon-snow) and 7 × 10−4 m−1 (night-rainy). We have shown that developed Gaussian decomposition method certainly improves DIAL-data processing.