2002 Annual

Wednesday, 16 January 2002: 3:30 PM
Multiple Instrument Sky Condition Algorithm
Pekka Ravila, Vaisala Oyj, Helsinki, Finland; and J. Heinonen and J. Räsänen
An innovative sky condition algorithm based on data from multiple instruments has been developed by Vaisala. The new algorithm utilizes the data from several different ceilometers or combines the ceilometer data with sky coverage information collected by an infrared scanning instrument. The algorithm can adjust to any number of instruments available.

Combining the data from different instruments enables improved automatic sky condition reporting, which takes a further step towards the automation of routine weather observations. Large airports often have several ceilometers with a few kilometers distance from each other. This offers a readily available source for multiple instrument data.

The new infrared scanning instrument developed by Vaisala offers another solution to overcome the limitations of the one-point ceilometer data. By measuring the variation in infrared radiation levels in different directions and with different elevation angles, the instrument can determine the total cloud coverage for the whole visible sky. Combining the coverage data with the cloud height data from ceilometers available the cloud layer information can be computed.

The new algorithm has shown good results in comparison to sky condition reported by human observers. A clear improvement against the single instrument approach is obtained.

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