Opto-acoustic sounding of the atmospheric parameters

Abstract

Experimental investigations of sound pulse generation accompanying the propagation of high-power pulsed laser radiation in the atmosphere were started at the IAO SB RAS in 1986. Based on these investigations, new opto-acoustic methods of sounding of the atmospheric temperature, wind velocity, relative humidity, and number density of micron fraction of atmospheric aerosols were suggested. A source of the acoustic signal in an opto-acoustic sounding system is a discrete laser spark made by focusing a CO2 laser beam into the atmosphere at distances up to 500 m. The number density of coarsely dispersed aerosols was determined from the number of pulses in the acoustic signal generated by the discrete laser spark. Results of opto-acoustic measurements of the number density of coarsely dispersed aerosols agree well with the microphysical model of aerosol atmosphere for Western Siberia. A threshold laser energy density resulting in the origin of local plasma formations is about 6−10 J /cm2. For lower laser energy densities, the acoustic radiation is generated due to laser-induced thermal expansion of the propagation medium. The measurable parameters are the effective laser beam radius, the coefficient of laser radiation absorption, and the total laser beam energy.