Lidar inelastic multiple-scattering parameters of cirrus particle ensembles determined with geometrical-optics crystal phase functions

Multiple-scattering correction factors for cirrus particle extinction coeff icients measured with Raman and high spectral resolution lidars are calcula ted with a radiative-transfer model. Cirrus particle-ensemble phase functio ns are computed from single-crystal phase functions derived in a geometrica l-optics approximation. Seven crystal types are considered. In cirrus cloud s with height in dependent particle extinction coefficients the general pat tern of the multiple-scattering parameters has a steep onset at cloud base with values of 0.5-0.7 followed by a gradual and monotonic decrease to 0.1- 0.2 at cloud top. The larger the scattering particles are, the more gradual is the rate of decrease. Multiple-scattering parameters of complex crystal s and of imperfect hexagonal columns and plates can be well approximated by those of projected-area equivalent ice spheres, whereas perfect hexagonal crystals show values as much as 70% higher than those of spheres. The depen dencies of the multiple-scattering parameters on cirrus particle spectrum, base height, and geometric depth and on the lidar parameters laser waveleng th and receiver field of view, are discussed, and a set of multiple-scatter ing parameter profiles for the correction of extinction measurements in hom ogeneous cirrus is provided. (C) 2000 Optical Society of America.