Spectro-polarimetric backscattering of atmospheric particles

Abstract

This study presents a new experiment to measure the polarization-resolved two-dimensional light-scattering patterns, near and including the backscattering direction, of fixed particles representative of some atmospheric-aerosol types. The measurements are conducted across a broad spectrum, from 450 to 850 nm, and for different polarization states. A supercontinuum laser, achromatic optics, and polarizers are used to measure the scattering patterns. Important quantities for applications such as lidar are also measured including the backscattering phase-function and the linear depolarization ratio in the exact backscattering direction. Microscopic images of the particles are provided by digital in-line holography as well. Thus, in some cases, it is possible to interpret the spectro-polarimetric measurements with knowledge of the size and shape of the particles involved. Spherical particles of known properties are used to calibrate the method. Then, Arizona test dust, Gobi and Sahara Desert dust, and ash from the Eyjafjallajökull and La Palma volcanic eruptions are studied to illustrate the method's potential for lidar applications.