NSA/VCEIL/C1 - poor sensitivity at low altitude

The ceilometer has an internal amplifier that it sets to low or high depending on 
prevalant conditions. Normally, the gain is automatically set high during clear skies. It appears 
that during these times, a slight degradation in either the transmitter or receiver is 
being amplified and produces a "ripple" at low altitudes in the backscatter plot. Cloud 
base height detection is not affected.

• receiver_sensitivity
• Normalized corrected relative backscatter(backscatter)

NSA/VCEIL/C1 - Degraded window

The ceilometer continuously gave warnings for window contamination because the window had 
deteriorated. Cloud base height detection did not appear to be significantly affected. 
The window conditioner was replaced on 8/11/09 but this did not clear the warning. The 
instrument was replaced.

• Third cloud base height(third_cbh)
• alt_highest_signal
• Second lowest cloud base height(second_cbh)
• status_flag
• sum_backscatter
• Lowest cloud base height detected.(first_cbh)
• Normalized corrected relative backscatter(backscatter)
• status_string
• background_light
• vertical_visibility
• window_contamination

NSA/VCEIL/C1/C2 - Reprocess: Incorrect serial_number and sum_backscatter fields

Attribute serial_number: In most cases, this field is not representative of the actual 
serial number of the instrument because the value did not change when an instrument changed 
locations or was replaced with a spare.
   
Variable sum_backscatter: An out-of-range condition for the "sum of detected and 
normalized backscatter" was reported as 0 instead of missing (-9999). The valid range is 0 - 
0.0999 /srad.
   
This DQR also applies to a1 and b1 level data collected prior to the begin date.

• sum_backscatter

• sum_backscatter