J5.3
Active Probing of Cloud Thickness, Optical Depth and Absorption Properties using Wide-Angle Imaging Lidar
Steven P. Love, LANL, Los Alamos, NM; and A. B. Davis, C. A. Rhode, L. Teller, and C. Ho
For remote sensing of cloud properties, traditional "on-beam" lidar, which collects returns from only a very narrow field of view centered on the transmitted laser beam, yields only a small fraction of the information potentially available. Since, at most optical wavelengths, laser photons are not absorbed but merely scattered out of the beam, eventually escaping the cloud via multiple scattering, much additional information is available in the light scattered far from the input beam. Monitoring these "off-beam" returns in a fully space- and time-resolved manner is the essence of our unique instrument, Wide Angle Imaging Lidar (WAIL). Incorporating a high-speed micro-channel-plate imaging detector system, and having a 60-degree full-angle field of view, WAIL, in effect, produces "movies" of the scattering process and records the cloud’s radiative Green functions. A direct product of WAIL is the distribution of photon path lengths resulting from multiple scattering in the cloud, hence new insights into cloud absorption processes. Following guidance from photon diffusion theory, we can use the measured Green functions to infer the physical thickness and optical depth of the cloud layer, and, from there, estimate the volume-averaged liquid water content. WAIL is notable in that it is applicable to optically thick clouds, a regime in which traditional lidar is reduced to ceilometry and mm-radar is prone to modeling error when translating microwave reflectivities into optical quantities. We will present recent WAIL data on various clouds and discuss the extension of WAIL to full diurnal monitoring by means of an ultra-narrow magneto-optic atomic line filter for daytime measurements.
Joint Session 5, Remote Sensing of Clouds III (Joint between 11th Cloud Physics and 11th Atmospheric Radiation)
Friday, 7 June 2002, 3:30 PM-5:00 PM
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