Paired Ground-Based Hemispherical Observations for Cloud Base Height Estimation

Kassianov, E. and Long, C.N., Pacific Northwest National Laboratory
Thirteenth Atmospheric Radiation Measurement (ARM) Science Team Meeting

Cloud base height (CBH) is one of the primary factors that governs the downwelling longwave radiative properties of clouds. Ground-based cloud radar and lidar measurements provide valuable information about cloud boundaries. However, these measurements are expensive and zenith-pointing with a very narrow field-of-view (FOV), whereas our surface radiation uses a hemispherical FOV. Due to their cost and the lack of availability of cloud radars and lidars, these measurements are limited to a few established surface sites. Further, these zenith-pointing measurements suffer from inhomogeneous sampling characteristics. In other words, derived cloud properties (for a given zenith point) may not be representative for an area surrounding these ground-based instruments that influences the corresponding irradiance measurements. For these reasons, it is highly desirable to have a method for measuring CBH that avoids the above limitations. This method should be inexpensive and provide non-zenith pointing (under FOV) observations. We suggest a method based on paired ground-based Total Sky Imagers hemispherical observations. The suggested method has been evaluated by using both the model-output inverse problem and data from Cloudiness Inter-Comparison IOP (Oklahoma, 2003). This poster presents some preliminary results of this validation.

Note: This is the poster abstract presented at the meeting; an extended version was not provided by the author(s).