TWP/MPl/C2 - Laser power failure events

When the new laser for the MPL at Nauru was installed the handset was incorrectly set to
manual instead of automatic. This meant that when the power was interrupted to the I van 
(even

observers when they saw no laser light. This went on from 29 Jan at 23:00

• Aerosol backscatter coefficient at 355 nm(backscatter)

TWP/MPL/C2 - Power outage in I-Van resulted in Missing Data

I forgot to put in the daily report that we took the I van down yesterday to replace the 
fans
in the Clary UPS. This was from 2300z on 24May03 to 0010z on 25May03. Instruments affected 
:

MPL
Ceilometer
MWR
WSI
TSI

Rex

• Time offset of tweaks from base_time(time_offset)
• base time(base_time)
• MPL Cloth et al. Algorithm Significance Mask(SigniMaskMplCloth)
• Height of Center of Each Range Bin(Heights)

• null(Raw data stream - documentation not supported)

• time(time)
• Laser Temperature(laser_temp)
• Repetition rate, or Trigger Frequency of the laser(trigger_freq)
• Maximum altitude retrieved from multichannel scalar card.(max_altitude)
• Sum of raw backscatter counts per bin prior to ANY corrections.(total_counts)
• Time in nanoseconds for each range bin of multichannel scalar card.(range_bin_time)
• Angle of inclination with respect to horizontal(transceiver_altitude_angle)
• Background Signal(background_signal)
• Laser output energy per pulse(energy_monitor)
• Number of laser shots recorded(shots_summed)
• Angle of orientation with respect to true geographic north(transceiver_azimuth_angle)
• Voltage level which operates the A/D card and the detector(voltage_05)
• Amount of time laser pulse lags behind the scalar trigger(laser_scalar_sync_offset)
• Time offset of tweaks from base_time(time_offset)
• Voltage level which operates the thermistor(voltage_10)
• lon(lon)
• base time(base_time)
• lat(lat)
• Width of range-bins calculated from range_bin_time(range_bin_width)
• Dummy altitude for Zeb(alt)
• required to correct raw counts for detector deadtime prior to all other
  corrections.(deadtime_correction)
• Amount of time the scalar lags behind the sync trigger(scalar_sync_offset)
• Distance from leading edge of first range bin to the center of each bin .(range_bins)
• Aerosol backscatter coefficient at 355 nm(backscatter)
• Preliminary cloud base height(preliminary_cbh)
• Number of laser pulses summed during measurement interval(shots_sum)
• Array of heights for the range gates(height)
• Detector Temperature(detector_temp)
• Instrument Temperature(instrument_temp)
• range(range)
• Repetition Rate, or Trigger Frequency of the laser(pulse_rep)
• Voltage level which operates the energy monitor(voltage_15)
• Filter Temperature(filter_temp)
• effective range offset due to poor sync between laser firing and A/D trigger.(range_offset)
• value represents date of last configuration change as yyyymmdd(property)
• Amount of time the actual laser pulse lags behind the sync trigger(laser_sync_offset)

• MPL Cloth et al. Algorithm Cloud Mask(CloudMaskMplCloth)
• Height of Center of Each Range Bin(Heights)
• base time(base_time)
• Time offset of tweaks from base_time(time_offset)

TWP/MPL/C2 - laser diode failure

On Nov 20, 2001, following a data gap of several hours the MPL energy monitor reading 
showed an abrupt decrease of about 60%.  The laser energy continued to decrease to a reading 
of zero by Nov 23.  Cloud detection is satisfactory through Nov 21, but is not 
satisfactory after this time until the laser diode was replaced on Jan 08, 2002.  Data between the 
dates of 2001-11-22 and 2002-01-08 inclusive is not useful.

• Time offset of tweaks from base_time(time_offset)
• lat(lat)
• Preliminary cloud base height above ground level(cbh)
• base time(base_time)
• Dummy altitude for Zeb(alt)
• lon(lon)

• Time offset of tweaks from base_time(time_offset)
• base time(base_time)
• MPL Cloth et al. Algorithm Significance Mask(SigniMaskMplCloth)
• Height of Center of Each Range Bin(Heights)

• null(Raw data stream - documentation not supported)

• null(Raw data stream - documentation not supported)

• Instrument Temperature(instrument_temp)
• Laser Temperature(laser_temp)
• Repetition Rate, or Trigger Frequency of the laser(pulse_rep)
• Cloud base height, measured by MPL(cloud_base_height)
• base time(base_time)
• Flag indicating whether the beam was extinguished at indicated cloud top(cloud_top_attenuation_flag)
• Relative random error in backscatter profiles(random_error)
• Detector Temperature(detector_temp)
• lon(lon)
• Cloud mask(cloud_mask_1)
• Array of heights for the range gates(height)
• lat(lat)
• Background Signal(background_signal)
• Cloud mask(cloud_mask_2)
• Aerosol backscatter coefficient at 355 nm(backscatter)
• Dummy altitude for Zeb(alt)
• Laser output energy per pulse(energy_monitor)
• Time offset of tweaks from base_time(time_offset)
• Number of laser shots recorded(shots_summed)
• The update time of the historical baseline used for the cloud boundary
  determination of this sample(baseline_update_time)
• cloud top height(cloud_top_height)

• time(time)
• Repetition rate, or Trigger Frequency of the laser(trigger_freq)
• Maximum altitude retrieved from multichannel scalar card.(max_altitude)
• Angle of inclination with respect to horizontal(transceiver_altitude_angle)
• Laser output energy per pulse(energy_monitor)
• Amount of time laser pulse lags behind the scalar trigger(laser_scalar_sync_offset)
• Voltage level which operates the thermistor(voltage_10)
• Width of range-bins calculated from range_bin_time(range_bin_width)
• required to correct raw counts for detector deadtime prior to all other
  corrections.(deadtime_correction)
• Distance from leading edge of first range bin to the center of each bin .(range_bins)
• Aerosol backscatter coefficient at 355 nm(backscatter)
• Number of laser pulses summed during measurement interval(shots_sum)
• Preliminary cloud base height(preliminary_cbh)
• Detector Temperature(detector_temp)
• Instrument Temperature(instrument_temp)
• Filter Temperature(filter_temp)
• Laser Temperature(laser_temp)
• Sum of raw backscatter counts per bin prior to ANY corrections.(total_counts)
• Time in nanoseconds for each range bin of multichannel scalar card.(range_bin_time)
• Background Signal(background_signal)
• Number of laser shots recorded(shots_summed)
• Angle of orientation with respect to true geographic north(transceiver_azimuth_angle)
• Voltage level which operates the A/D card and the detector(voltage_05)
• Time offset of tweaks from base_time(time_offset)
• lon(lon)
• base time(base_time)
• lat(lat)
• Dummy altitude for Zeb(alt)
• Amount of time the scalar lags behind the sync trigger(scalar_sync_offset)
• Array of heights for the range gates(height)
• range(range)
• Voltage level which operates the energy monitor(voltage_15)
• Repetition Rate, or Trigger Frequency of the laser(pulse_rep)
• effective range offset due to poor sync between laser firing and A/D trigger.(range_offset)
• value represents date of last configuration change as yyyymmdd(property)
• Amount of time the actual laser pulse lags behind the sync trigger(laser_sync_offset)

• MPL Cloth et al. Algorithm Cloud Mask(CloudMaskMplCloth)
• Height of Center of Each Range Bin(Heights)
• base time(base_time)
• Time offset of tweaks from base_time(time_offset)

TWP/MPL/C2 - Sun-shade dropping during daytime

The MPL sunshade began to act erratically on 9/15/2003 dropping frequently throughout day 
and night.  To reduce data loss, the sunshade was restrained from blocking the MPL during 
the night.  Thus, cloud detection during the night is satisfactory, but daytime 
measurements are frequently interspersed with episodes of beam-block.

• Time offset of tweaks from base_time(time_offset)
• base time(base_time)
• MPL Cloth et al. Algorithm Significance Mask(SigniMaskMplCloth)
• Height of Center of Each Range Bin(Heights)

• null(Raw data stream - documentation not supported)

• time(time)
• Laser Temperature(laser_temp)
• Repetition rate, or Trigger Frequency of the laser(trigger_freq)
• Maximum altitude retrieved from multichannel scalar card.(max_altitude)
• Sum of raw backscatter counts per bin prior to ANY corrections.(total_counts)
• Time in nanoseconds for each range bin of multichannel scalar card.(range_bin_time)
• Angle of inclination with respect to horizontal(transceiver_altitude_angle)
• Background Signal(background_signal)
• Laser output energy per pulse(energy_monitor)
• Number of laser shots recorded(shots_summed)
• Angle of orientation with respect to true geographic north(transceiver_azimuth_angle)
• Voltage level which operates the A/D card and the detector(voltage_05)
• Amount of time laser pulse lags behind the scalar trigger(laser_scalar_sync_offset)
• Time offset of tweaks from base_time(time_offset)
• Voltage level which operates the thermistor(voltage_10)
• lon(lon)
• base time(base_time)
• lat(lat)
• Width of range-bins calculated from range_bin_time(range_bin_width)
• Dummy altitude for Zeb(alt)
• required to correct raw counts for detector deadtime prior to all other
  corrections.(deadtime_correction)
• Amount of time the scalar lags behind the sync trigger(scalar_sync_offset)
• Distance from leading edge of first range bin to the center of each bin .(range_bins)
• Aerosol backscatter coefficient at 355 nm(backscatter)
• Preliminary cloud base height(preliminary_cbh)
• Number of laser pulses summed during measurement interval(shots_sum)
• Array of heights for the range gates(height)
• Detector Temperature(detector_temp)
• Instrument Temperature(instrument_temp)
• range(range)
• Repetition Rate, or Trigger Frequency of the laser(pulse_rep)
• Voltage level which operates the energy monitor(voltage_15)
• Filter Temperature(filter_temp)
• effective range offset due to poor sync between laser firing and A/D trigger.(range_offset)
• value represents date of last configuration change as yyyymmdd(property)
• Amount of time the actual laser pulse lags behind the sync trigger(laser_sync_offset)

• MPL Cloth et al. Algorithm Cloud Mask(CloudMaskMplCloth)
• Height of Center of Each Range Bin(Heights)
• base time(base_time)
• Time offset of tweaks from base_time(time_offset)

TWP/MPL/C2 - Reprocess: Global metadata error

During the time period specified, the global metadata attribute "averaging_int" is 
reported as 30 seconds when the value for this attribute should be 60 seconds.

• Time offset of tweaks from base_time(time_offset)

TWP/MPL/C2 - Optical throughput unacceptable

The optical throughput of the MPL at Nauru is below an acceptable level. Despite an 
extended stay to address the problem in Feb 2003, the problem was unresolved.  An additional 
repair was attempted in July 2003 with no significant success.  Several optical components 
were replaced and the system was repeatedly re-aligned.  

The system appears to have been properly collimated as the shape of the signal is 
appropriate for both near and far range.  The magnitude of the signal was simply too low.  This 
signal decrease was apparent in ambient background values as well as from atmospheric 
signal, so the impact on data quality was not as severe as might otherwise be the case.  The 
MPL was still capable of detecting high altitude cirrus (day and night) but the 
sensitivity was reduced.

• null(Raw data stream - documentation not supported)

• Attenuated backscatter(detector_counts)

TWP/MPL/C2 - Detector on instrument failed.

The detector on the MPL failed. The result are zeros for the detector counts data.

• null(Raw data stream - documentation not supported)

• Attenuated backscatter(detector_counts)

TWP/MPL/C2 - Missing data

The MPL was turned off due to a dead detector.

• null(Raw data stream - documentation not supported)

• time(time)
• Laser Temperature(laser_temp)
• Repetition rate, or Trigger Frequency of the laser(trigger_freq)
• Maximum altitude retrieved from multichannel scalar card.(max_altitude)
• Sum of raw backscatter counts per bin prior to ANY corrections.(total_counts)
• Time in nanoseconds for each range bin of multichannel scalar card.(range_bin_time)
• Angle of inclination with respect to horizontal(transceiver_altitude_angle)
• Background Signal(background_signal)
• Laser output energy per pulse(energy_monitor)
• Number of laser shots recorded(shots_summed)
• Angle of orientation with respect to true geographic north(transceiver_azimuth_angle)
• Voltage level which operates the A/D card and the detector(voltage_05)
• Amount of time laser pulse lags behind the scalar trigger(laser_scalar_sync_offset)
• Time offset of tweaks from base_time(time_offset)
• Voltage level which operates the thermistor(voltage_10)
• lon(lon)
• base time(base_time)
• lat(lat)
• Width of range-bins calculated from range_bin_time(range_bin_width)
• Dummy altitude for Zeb(alt)
• required to correct raw counts for detector deadtime prior to all other
  corrections.(deadtime_correction)
• Amount of time the scalar lags behind the sync trigger(scalar_sync_offset)
• Distance from leading edge of first range bin to the center of each bin .(range_bins)
• Aerosol backscatter coefficient at 355 nm(backscatter)
• Preliminary cloud base height(preliminary_cbh)
• Number of laser pulses summed during measurement interval(shots_sum)
• Array of heights for the range gates(height)
• Detector Temperature(detector_temp)
• Instrument Temperature(instrument_temp)
• range(range)
• Assumed zero-range bin number\(assumed_zero_range_bin)
• Attenuated backscatter(detector_counts)
• Repetition Rate, or Trigger Frequency of the laser(pulse_rep)
• Voltage level which operates the energy monitor(voltage_15)
• Filter Temperature(filter_temp)
• effective range offset due to poor sync between laser firing and A/D trigger.(range_offset)
• value represents date of last configuration change as yyyymmdd(property)
• Amount of time the actual laser pulse lags behind the sync trigger(laser_sync_offset)

TWP/MPL/C2 - Intermittent Double Pulse from laser

When Spectra Physics discontinued support for their laser diode power supply, an 
alternative was need to extend the usefulness of the Spectra Physics laser head inside the MPLs.  
The solution was to use a Coherent laser diode. Unfortunately, the Coherent diode lasers 
do not have the exact same characteristics as the Spectra Physics diode lasers. As a 
result, the output of the Spectra Physics laser head sometimes produces a second pulse close 
in time but lower in intensity from the first main pulse. This is known as ?double pulsing?.

Not all of the Spectra Physics/Coherent combination systems produce a double pulse and the 
systems that do produce a double pulse do not always exhibit this behavior. It can be 
identified by a second peak at ~.2km. At first glance the signal in the data will resemble 
a low aerosol or cloud layer. When the double pulse is weak, the atmospheric signal will 
obscure the double pulse signal. At the ARM sites with a sunshade such as TWP and AMF, 
the double pulse can be seen when the sunshade closes during solar noon. When the sunshade 
closes, the MPL does not see atmospheric signal so the second pulse is evident. At SGP, a 
daily window cleaning is part of the routine. During this time the double pulse can be 
seen. Without a sunshade or window cleaning it is impossible to say definitively if double 
pulse is present. 

The first system to produce a double pulse was MPL s/n 008 located at TWP ? C2 Nauru in 
February 2005. The second system was MPL s/n 004 located at SGP in August 2005. The 
potential for the other systems to produce a double pulse is high. However, as of March 2006, 
the MPLs at NSA, TWP ? C1, TWP ? C3 and AMF have not recorded data with the double pulse 
artifact.  

The ARM program is in the process of replacing all the MPLs with a newer model. After the 
new MPLs are deployed the double pulse problem should not be an issue. The old systems 
will be relegated as spares. The double pulse problem will return if an old system is 
needed to replace a failed new system.

• Attenuated backscatter(detector_counts)