NSA/VCEIL/C1 - Reprocess: Intermittent data and clock drift

The available processed data for the NSA.C1 VCEIL for the time period indicated are 
incomplete.  The raw data is largely complete but pre-processing is required before these data 
can be reprocessed to produce a complete netcdf data set.

While awaiting the reprocessed data set, the intermittent data are available from the ARM 
Archive.  Users should be aware that the data are additionally compromised by a clock 
drift of at least 10 minutes, though this likely has little affect on cloud detection 
results.  The clock drift will not be addressed by the reprocessing.

Note also, that the clock drift was corrected at the end of the DQR period, but it may 
have existed before the beginning of the DQR period.

The data for this period should be used with caution.

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

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.

• Percentage of nominal factory setting (0 to 999%)(receiver_sensitivity)
• Aerosol volume backscattering coefficient at 355 nm(backscatter)