Complex Index of Refraction of Airborne Fly Ash Determined by Laser Radar and Collection of Particles at 13 km

Abstract

On 30 September 1970, the National Center for Atmospheric Research (NCAR) obtained data on the vertical distribution of particulate material over Boulder, Colo., from laser radar soundings and simultaneous airborne particle collections. A layer of particulate material at about 13 km was of special interest. Particles in this layer differed from normal tropospheric particles and were probably fly ash created by forest fires in California during the previous week. A technique for determining the complex index of refraction of atmospheric particles has been applied to the 13-km data. By assuming the real part of the refractive index to be 1.55, the imaginary part (the absorption parameter) is estimated to be 0.044±0.011.