DQRID : D060221.1
Start DateStart TimeEnd DateEnd Time Data Quality Metric
NIM/MPL/M1 - False Positive Cloud Base Height Values During Solar Noon
DataStreams:nimmplM1.a1, nimmplM1.00
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 
During solar noon all cloud base values are suspect. A visual inspection of the 

backscatter data is necessary to determine if a cloud is present. If a cloud not seen in the 
backscatter data the cloud base value should be ignored.
  • preliminary_cbh
  • Raw data stream - documentation not supported

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