THOR -: Cloud Thickness from Offbeam lidar Returns

被引:37
作者
Cahalan, RF [1 ]
McGill, M
Kolasinski, J
Várnai, T
Yetzer, K
机构
[1] NASA, Goddard Space Flight Ctr, Atmospheres Lab, Greenbelt, MD 20771 USA
[2] Univ Maryland, Joint Ctr Earth Syst Technol, Baltimore, MD 21201 USA
[3] SSAI, Raytheon, Lanham, MD USA
关键词
D O I
10.1175/JTECH1740.1
中图分类号
P75 [海洋工程];
学科分类号
0814 ; 081505 ; 0824 ; 082401 ;
摘要
Conventional wisdom is that lidar pulses do not significantly penetrate clouds having an optical thickness exceeding about tau = 2, and that no returns are detectible from more than a shallow skin depth. Yet optically thicker clouds Of tau >> 2 reflect a larger fraction of visible photons and account for much of the earth's global average albedo. As cloud-layer thickness grows, an increasing fraction of reflected photons are scattered multiple times within the cloud and return from a diffuse concentric halo that grows around the incident pulse, increasing in horizontal area with layer physical thickness. The reflected halo is largely undetected by narrow field-of-view (FOV) receivers commonly used in lidar applications. Cloud Thickness from Offbeam Returns (THOR) is an airborne wide-angle detection system with multiple FOVs, capable of observing the diffuse halo as a wide-angle signal, from which the physical thickness of optically thick clouds can be retrieved. This paper describes the THOR system, demonstrates that the halo signal is stronger for thicker clouds, and presents a validation of physical thickness retrievals for clouds having tau > 20, from NASA's P-3B flights over the Department of Energy's Atmospheric Radiation Measurement Southern Great Plains site, using the lidar, radar, and other ancillary ground-based data.
引用
收藏
页码:605 / 627
页数:23
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