NIM/MPL/M1 - False Positive Cloud Base Height Values During Solar Noon

As the laser ages, the output reduces.  This lowers the signal to noise ratio. The lower 
signal to noise ratio interferes with the cloud base height algorithm to correctly 
determine if a cloud is actually present. During solar noon the signal to noise ratio is the 
lowest. This condition results in many false positive values. The values start at a high 
altitude and progressively get lower as the sun gets to zenith. The trend reverses as the 
sun passes. The pattern in the data resembles a ?V? shape starting 2 hours before solar 
noon to 2 hour past. A low incident of false positive values exists from 20051227. However, 
the condition becomes prominent on 20060303 - 20060420. The cloud base calibration table 
was modified to compensate for the lower signal to noise levels. 

Note: If a cloud is actually present, the cloud base algorithm will determine the height 
and report correctly. The false positive values are only a concern during cloud free 
conditions.

• Raw data stream - documentation not supported

• Preliminary cloud base height above ground level(preliminary_cbh)