4.1
Towards improved ceilometer-based observations of sky cover
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A decade-long analysis containing more than 29,000 daytime cloud observations was undertaken using data from the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) climate research facility. Observations from a ceilometer were compared to a collocated Total Sky Imager (TSI), a visible wavelength camera that obtains sky cover through digital image analysis. Observations were sorted into the standard bins of clear, few, scattered, broken, and overcast based on the percentage of cover.
Overall, only 58% of the observations were placed into the same category by both instruments. The ceilometer recorded close to 70% more clear sky observations than the TSI does, likely due to limited ability of the ceilometer to detect high and thin clouds. Digital image processing techniques and statistical analysis will be used on cases with large discrepancies to determine the cloud types and meteorological conditions that are prone to causing observation errors, and a new model for calculating sky cover based on a regression of ceilometer and surface meteorology observations will be presented.