Abstract

The University of Wisconsin High Spectral Resolution Lidar (HSRL) directly measures aerosol¹ and cloud particle² backscatter cross sections, optical depths, and backscatter phase functions. The HSRL technique spectrally separates the lidar return into molecular and aerosol scattering contributions. This is possible because the backscatter spectrum from molecules is Doppler-broadened by thermal motions. Particles are more massive than molecules, thus exhibit slower Brownian motions which produce insignificant broadening of the backscatter spectrum. Using the known distribution of atmospheric density (from available radiosonde or climatology), the molecular scattering cross section is calculated and provides a calibration target available at every range. Extinction is unambiguously determined from the range dependent decrease in the molecular backscatter intensity. The ratio of particle to molecular backscatter intensities provides the particle backscatter cross section at each range. Whenever gaseous and particle absorption are negligible, the particle backscatter phase function is directly determined.

© 1990 Optical Society of America