Evaluating the Utility of Spectral Shortwave Zenith Radiance Data for Cloud Property Retrieval

Description

Measurement of spectral zenith radiance is potentially powerful tool for ground-based remote sensing of cloud microphysical properties. In contrast with more traditional hemispheric irradiance measurements, instruments for zenith radiance can be deployed at sites with significant horizontal obstructions to the field of view, and can also be used to study individual broken clouds. However, the radiative transfer problem is potentially much more complicated due to three-dimensional effects, particularly for optically thin broken clouds, and also due to the fact that the monochromatic radiance solution as a function of cloud optical depth is not single-valued. The radiative transfer problem for hemispheric irradiance is much less demanding, and has a longer track record in the scientific literature. In this study we compare cloud property retrievals from both zenith radiance and hemispheric irradiance, as measured by the Shortwave Array Spectroradiometers (SAS) at the Southern Great Plains site. We compare the retrievals for solid overcast skies, where both approaches are conceptually valid.