Daytime Lidar Characterization of Subvisual Cirrus Layers

A mobile Rayleigh lidar facility was used at two sites in the western United States to detect and characterize subvisual cirrus layers by analyzing the separated polarization components of the signal. The polarized scatter was range gated and used for optical attenuation measurements of visual cirrus, and the depolarized signal was used for sensitive detection of subvisual cirrus. For temporal windows of 1 minute the optical density sensitivity was 0.02, slightly larger than the optical density of subvisual cirrus layers. The optical densities of the subvisual layers were calculated using a backscatter to extinction ratio calculated from visual cirrus layers or by temporal averaging of uniform layers. Using a combination of temporal averaging and a backscatter to extinction ratio improved the optical density sensitivity by seven orders of magnitude.