Design Of A Fluorescence Lidar For Biological Aerosol Detection And Preliminary Experimental Results

Atmospheric bioaerosols exist in the troposphere,mainly composed of tiny organic particles such as bacteria,fungi,viruses and dust mites.Compared with ordinary aerosols,their diffusion and propagation in the air may cause greater harm on the atmospheric environment,such as the epidemic of diseases between humans and animals and plants,and the detection of biological aerosols is of great urgency.As a new remote sensing method,lidar has high accuracy and high spatial and temporal resolution*Combined with laser induced biological aerosol fluorescence effect,fluorescence lidar provides powerful support for remote sensing of atmospheric aerosol.This thesis is devoted to the study of the theoretical research of the biological aerosol fluorescence lidar,aiming to design and construct a fluorescence laser radar system for detecting biological aerosol.Based on the principle of fluorescence lidar detection,the detailed explanation of the lidar equation and the concrete solution of the equation are given.A series of performance simulations are carried out for the selection of laser induced wavelength.Using UV 355nm and 266nm laser as the excitation source respectively,the models of the biological aerosol fluorescence lidar monitoring system are constructed.The effects of different excitation band,ozone absorption and solar background light on the detection effect of laser radar fluorescence are considered,and the performance of the system is simulated and analyzed.The excitation fluorescence of the 355nm band is greatly influenced by the daytime sun background light,and its corresponding lidar system can get better effect during the night detection,while the excitation band of 266nm can inhibit the influence of the background light well,and the corresponding lidar system can realize the effective daytime detection of the biological aerosol.In this work,we employ 266nm laser as excited sources to achieve the aim of nighttime and daytime measurements.Based on the numerical simulations,the fluorescence lidar system has been developed at Xi'an University of Technology.With continuous observations of atmospheroc biological aerosols over Xi'an,the effective bands of the fluorescence signal were obtained.The maximum effective detection distance of the Mie-Rayleigh signals is about 2.5km,while the detection distance of the fluorescence signal is about 0.9km.Aerosol extinction coefficient profiles and number concentration profiles of biological aerosols were also retrieved,with a maximum value of 5340 particles/m3.Experiments verified the feasibility of the system design,and paved the way for long-term experimental observations.