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.
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.