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.

• Lowest cloud base height detected.(first_cbh)
• Vertical visibility(vertical_visibility)
• Aerosol volume backscattering coefficient at 355 nm(backscatter)
• SUM of detected and normalized backscatter(sum_backscatter)
• Second lowest cloud base height(second_cbh)
• Third cloud base height(third_cbh)
• Percentage of nominal factory setting (0 to 999%)(receiver_sensitivity)
• Altitude of highest signal(alt_highest_signal)
• Millivolts at internal ADC input (0 to 2500)(background_light)

TWP/VCEIL/C2 - Vceil computer disconnected

VCEIL computer was disconnected during this time period.

• Aerosol volume backscattering coefficient at 355 nm(backscatter)
• Flag indicating aeri retrieval status(status_flag)
• Percentage of nominal factory setting (0 to 999%)(laser_pulse_energy)
• Third cloud base height(third_cbh)
• Time offset of tweaks from base_time(time_offset)
• Time offset from base_time(base_time)
• Lowest cloud base height detected.(first_cbh)
• Warning and alarm status bits(status_string)
• distance to center of range bin after correcting for offset in sync(range)
• Millivolts at internal ADC input (0 to 2500)(background_light)
• Percentage of nominal factory setting (0 to 999%)(receiver_sensitivity)
• Vertical visibility(vertical_visibility)
• Laser temperature(laser_temperature)
• Altitude of highest signal(alt_highest_signal)
• 6 character string describing instrument measurement parameters(measurement_parameters)
• Second lowest cloud base height(second_cbh)
• GPS raw data filename(filename)
• Degrees from vertical (-15 to +90)(tilt_angle)
• Detection status. See details(detection_status)
• Millivolts at internal ADC input(window_contamination)
• SUM of detected and normalized backscatter(sum_backscatter)

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.

• Aerosol volume backscattering coefficient at 355 nm(backscatter)
• Flag indicating aeri retrieval status(status_flag)
• Percentage of nominal factory setting (0 to 999%)(laser_pulse_energy)
• Third cloud base height(third_cbh)
• Time offset of tweaks from base_time(time_offset)
• Time offset from base_time(base_time)
• Lowest cloud base height detected.(first_cbh)
• Warning and alarm status bits(status_string)
• distance to center of range bin after correcting for offset in sync(range)
• Millivolts at internal ADC input (0 to 2500)(background_light)
• Percentage of nominal factory setting (0 to 999%)(receiver_sensitivity)
• Vertical visibility(vertical_visibility)
• Laser temperature(laser_temperature)
• Altitude of highest signal(alt_highest_signal)
• 6 character string describing instrument measurement parameters(measurement_parameters)
• Second lowest cloud base height(second_cbh)
• Degrees from vertical (-15 to +90)(tilt_angle)
• Detection status. See details(detection_status)
• Millivolts at internal ADC input(window_contamination)
• SUM of detected and normalized backscatter(sum_backscatter)

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.

• Percentage of nominal factory setting (0 to 999%)(laser_pulse_energy)
• Vertical visibility(vertical_visibility)
• Aerosol volume backscattering coefficient at 355 nm(backscatter)
• SUM of detected and normalized backscatter(sum_backscatter)
• Laser temperature(laser_temperature)
• Millivolts at internal ADC input (0 to 2500)(background_light)

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.

• Second lowest cloud base height(second_cbh)
• Third cloud base height(third_cbh)
• Percentage of nominal factory setting (0 to 999%)(receiver_sensitivity)
• Altitude of highest signal(alt_highest_signal)
• Detection status. See details(detection_status)

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.

• Aerosol volume backscattering coefficient at 355 nm(backscatter)
• Vertical visibility(vertical_visibility)
• Altitude of highest signal(alt_highest_signal)
• Third cloud base height(third_cbh)
• Second lowest cloud base height(second_cbh)
• Millivolts at internal ADC input(window_contamination)

TWP/VCEIL/C2 - Receiver failure

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

• Aerosol volume backscattering coefficient at 355 nm(backscatter)
• Vertical visibility(vertical_visibility)
• Altitude of highest signal(alt_highest_signal)
• Third cloud base height(third_cbh)
• Second lowest cloud base height(second_cbh)
• Lowest cloud base height detected.(first_cbh)
• Millivolts at internal ADC input (0 to 2500)(background_light)
• SUM of detected and normalized backscatter(sum_backscatter)