SGP/VCEIL/C1 - poor signal

When parameters were changed (set noise_h2_compensation to "ON" and units to "METERS") to 
correct a low amplitude problem, the backscatter plots began displaying horizontal 
stripes indicating detector "ringing". However, the cloud base heights are not affected. The 
problem was corrected when the instrument was replaced.

• detection_status
• Backscatter(backscatter)

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
• Backscatter(backscatter)

TWP/VCEIL/C3 - low receiver sensitivity

The ceilometer reported frequent receiver alarms. There are periods when the receiver 
sensitivity dropped to about 50%. The problem was corrected by replacing the instrument with 
a spare.

• receiver_sensitivity
• Backscatter(backscatter)
• sum_backscatter
• Second lowest cloud base height(second_cbh)
• Third cloud base height(third_cbh)
• Lowest cloud base height detected.(first_cbh)
• background_light
• alt_highest_signal
• vertical_visibility

TWP/VCEIL/C2 - Vceil computer disconnected

VCEIL computer was disconnected during this time period.

• status_string
• detection_status
• sum_backscatter
• laser_pulse_energy
• tilt_angle
• alt_highest_signal
• filename
• laser_temperature
• vertical_visibility
• range
• Third cloud base height(third_cbh)
• measurement_parameters
• status_flag
• Second lowest cloud base height(second_cbh)
• Lowest cloud base height detected.(first_cbh)
• background_light
• Backscatter(backscatter)
• window_contamination
• base_time
• receiver_sensitivity
• time_offset

TWP/VCEIL/C2 - Time offset

On 7/14/2006, I found that the ceilometer time was 8m 36s slow, the PC time display (lower 
right taskbar) was frozen at "22:24", and AboutTime was not running. Corrected it on 
7/17 by running AboutTime so that 19:03:29 became 19:12:05. This also corrected the frozen 
display on the Windows98 taskbar. 

I am not sure of the start time of this problem but there were several other Windows 
related issues that had to be corrected on 5/14 with indications of inappropriate access via 
Remote Administrator on 5/13. I do not know if the time offset was a sudden or gradual 
change.

• status_string
• detection_status
• sum_backscatter
• laser_pulse_energy
• tilt_angle
• alt_highest_signal
• laser_temperature
• vertical_visibility
• range
• Third cloud base height(third_cbh)
• measurement_parameters
• Second lowest cloud base height(second_cbh)
• status_flag
• Lowest cloud base height detected.(first_cbh)
• background_light
• Backscatter(backscatter)
• window_contamination
• base_time
• receiver_sensitivity
• time_offset

TWP/VCEIL/C3 - standard instrument installed

A spare ceilometer without the tropics window option was installed. The manufacturer 
recommends the tropics window be used at +/- 25 deg lattitude to prevent direct solar 
radiation into the laser optics when the instrument pointed at zenith. No significant signal 
degradation is apparent during the autumnal equinox but, as a precaution, the unit was 
replaced with the original with a tropics window.

• Backscatter(backscatter)
• laser_pulse_energy
• laser_temperature
• sum_backscatter
• background_light
• vertical_visibility

TWP/VCEIL/C3 - Reduced sensitivity to high clouds

The instrument produced a significant number of optical cross-talk warnings and displayed 
a reduced capacity to detect high clouds.  The internal cables were inspected, the 
compensation fiber and optics monitor were replaced, the crosstalk compensation was adjusted, 
and the system tested with an optical termination hood, all with no improvement.  While 
waiting for a new receiver board, receiver ribbon cable, and compensation fiber cable from 
Vaisala, a spare ceilometer with a standard, "non-tropics", window was installed.

• receiver_sensitivity
• Second lowest cloud base height(second_cbh)
• Third cloud base height(third_cbh)
• detection_status
• alt_highest_signal

TWP/VCEIL/C2 - optical cross-talk compensation

The ceilometer gave frequent optical cross-talk compensation warnings, was insensitive to 
high clouds, and the tropics window was deteriorated. The instrument was replaced with a 
spare.

• Second lowest cloud base height(second_cbh)
• alt_highest_signal
• Backscatter(backscatter)
• window_contamination
• vertical_visibility
• Third cloud base height(third_cbh)

SGP/VCEIL/B6 - contaminated window

Backscatter has consistently high amplitude because the window was dirty. The problem was 
corrected when the window was cleaned.

• Third cloud base height(third_cbh)
• Lowest cloud base height detected.(first_cbh)
• Second lowest cloud base height(second_cbh)
• Backscatter(backscatter)

TWP/VCEIL/C2 - Receiver failure

The receiver failed and the instrument was replaced.  Data during the specified period are 
not valid.

• sum_backscatter
• Second lowest cloud base height(second_cbh)
• Lowest cloud base height detected.(first_cbh)
• alt_highest_signal
• Backscatter(backscatter)
• background_light
• vertical_visibility
• Third cloud base height(third_cbh)

TWP/VCEIL/C3 - Reduced sensitivity to high clouds

The instrument had reduced sensitivity to high clouds.

The instrument produced a significant number of optical cross-talk warnings and displayed 
a reduced capacity to detect high clouds. The window was cleaned and the instrument was 
power-cycled but with no improvement. Diagnostics indicated the problem was with the 
compensation fiber cable. 

The problem was corrected by replacing this standard-window instrument (that was tilted at 
16 degrees) with a tropics unit that became available.

• receiver_sensitivity
• Second lowest cloud base height(second_cbh)
• Third cloud base height(third_cbh)
• alt_highest_signal
• vertical_visibility

SGP/VCEIL/B6 - contaminated window

The window was contamined with bird droppings producing a status warning and causing the 
backscatter plot to have a higher than normal amplitude. The problem was corrected when 
the window was cleaned during regular preventative maintenance.

• Third cloud base height(third_cbh)
• Lowest cloud base height detected.(first_cbh)
• Second lowest cloud base height(second_cbh)
• sum_backscatter
• Backscatter(backscatter)
• alt_highest_signal
• vertical_visibility

SGP/VCEIL/B5 - Degraded hardware

Following repair at Vaisala and re-installation on 10/23/2007, the ceilometer experiencing 
intermittent receiver alarms and discontinuities in the backscatter plot. Vaisala 
recommended the old firmware card be replaced but that did not resolve the problems. The 
instrument was replaced with a spare and returned to the vendor for repair.

• detection_status
• laser_temperature
• Third cloud base height(third_cbh)
• status_flag
• background_light
• vertical_visibility
• Backscatter(backscatter)
• range
• sum_backscatter
• Second lowest cloud base height(second_cbh)
• receiver_sensitivity
• status_string
• measurement_parameters
• alt_highest_signal
• Lowest cloud base height detected.(first_cbh)
• laser_pulse_energy
• window_contamination
• tilt_angle

SGP/VCEIL/B5 - Missing data

Data are missing and unrecoverable.

• detection_status
• laser_temperature
• Third cloud base height(third_cbh)
• base_time
• status_flag
• lat
• background_light
• vertical_visibility
• Backscatter(backscatter)
• range
• sum_backscatter
• Second lowest cloud base height(second_cbh)
• lon
• receiver_sensitivity
• status_string
• measurement_parameters
• alt_highest_signal
• Lowest cloud base height detected.(first_cbh)
• laser_pulse_energy
• window_contamination
• time_offset
• tilt_angle
• alt

SGP/VCEIL/B4 - Window contamination

During this period, the VCEIL window repeatedly became contaminated by bird droppings 
shortly after each cleaning. Detection of clouds was intermittently limited. The window 
warnings are contained in the status_flag data.

The cleaning frequency was increased and then bird deterrent spikes were installed on 
3/24/2009. 

Cloud height measurements are suspect when the status_string field contains the "Window 
contaminated" warning.

• Backscatter(backscatter)
• Lowest cloud base height detected.(first_cbh)
• Third cloud base height(third_cbh)
• Second lowest cloud base height(second_cbh)
• vertical_visibility

GRW/VCEIL/M1 - Receiver failure

The AMF VCEIL had lower-than-normal laser transmitter power, ~84%, so the instrument was 
replaced with a spare on 4/22. The spare VCEIL had just been repaired but began to display 
receiver failure warnings.

Diagnostic information was sent to Vaisala and we discussed either replacing the receiver 
with the one from the original VCEIL (with the degraded transmitter) or replacing the 
transmitter in the original VCEIL with the one from the spare. Vaisala recommended the 
latter because the original VCEIL is a much newer unit.

On 5/16, the site operator replaced the transmitter in the original VCEIL with the one 
from the spare, realigned the optics, recalibrated the laser, and put the instrument back 
into service, successfully correcting the problem.

The data during this period were intermittently incorrect, containing warning flags and 
alarms and unreasonable cloud base heights.

• vertical_visibility
• Lowest cloud base height detected.(first_cbh)
• background_light
• Backscatter(backscatter)
• Third cloud base height(third_cbh)
• Second lowest cloud base height(second_cbh)
• alt_highest_signal

TWP/VCEIL/C1 - Compensation fiber

The VCEIL was reporting a "receiver optical cross-talk compensation is poor" warning. The 
window was cleaned and the instrument was power-cycled. The problem was corrected when 
the compensation fiber was replaced and ants were removed from communication connector.  
Cloud detection was impaired.

• Second lowest cloud base height(second_cbh)
• alt_highest_signal
• sum_backscatter
• receiver_sensitivity
• laser_pulse_energy
• Lowest cloud base height detected.(first_cbh)
• vertical_visibility
• Third cloud base height(third_cbh)
• Backscatter(backscatter)
• background_light

SGP/VCEIL/B1 - Warning flag

Beginning in 2000 (when this datastream was named sgpvceil25kB1.a1), the ceilometer was 
continuously giving warnings for low battery or charge voltage. Either the battery switch 
may not have been "ON" or the battery needed to be replaced. 

Attempts to correct the problem were unsuccessful until the time of site decommissioning. 
Maintenance efforts ceased 10/1/2009 and the battery was not checked prior to the site 
being decommissioned on 10/20/2009.

• status_flag

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)
• Backscatter(backscatter)
• status_string
• background_light
• vertical_visibility
• window_contamination

SGP/VCEIL/C1/B4/B5/B6 - 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 level data collected prior to b1 level.

• sum_backscatter

• sum_backscatter

• sum_backscatter

• sum_backscatter

SGP/VCEIL/B1 - 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 level data collected prior to b1 level.

• sum_backscatter

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

TWP/VCEIL/C1 - 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 level data.

• sum_backscatter

TWP/VCEIL/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 level data.

• sum_backscatter

TWP/VCEIL/C3 - 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 level data.

• sum_backscatter

NIM/VCEIL/M1 - 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.

• sum_backscatter

FKB/VCEIL/M1 - 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.

• sum_backscatter

HFE/VCEIL/M1 - 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.

• sum_backscatter

GRW/VCEIL/M1 - 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.

• sum_backscatter

HFE/VCEIL/S1 - 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.

• sum_backscatter

NSA/VCEIL/C1 - Small gaps in data

When the ceilometer was replaced, small gaps in the netCDF files occurred due to the 
presence of '?' characters in the backscatter and header records of the raw data that could 
not be ingested. It is unknown whether this was caused by a poor CPU board or 
incompatibilities with the computer configuration (hyper-threading). The problem was corrected when 
the instrument and computer were both replaced. 

During this period, approximately 3% of data are missing each hour due to this problem.

• Third cloud base height(third_cbh)
• alt_highest_signal
• laser_temperature
• receiver_sensitivity
• Second lowest cloud base height(second_cbh)
• Lowest cloud base height detected.(first_cbh)
• vertical_visibility
• tilt_angle
• time_offset
• measurement_parameters
• status_flag
• sum_backscatter
• range
• base_time
• Backscatter(backscatter)
• status_string
• background_light
• window_contamination
• detection_status
• laser_pulse_energy