TWP/MPL/C1 - Extended data gap

The lidar was taken off line because of problems with the site back-up
power generator.  The power issues have been resolved but the MPL
experienced an apparent computer problem and could not be started
remotely.  We have approximately 1 hour of data from December 11
(00-01 GMT). The RESET team visited Manus in February and got the
MPL going again on the 16th of that month.

• Voltage level which operates the A_D card and the detector(voltage_5)
• Laser Temperature(laser_temp)
• Voltage level which operates the thermistor(voltage_10)
• Preliminary cloud base height above ground level(cbh)
• Aerosol backscatter coefficient at 355 nm(backscatter)
• Number of laser shots recorded(shots_summed)
• Background Signal(background_signal)
• Instrument Temperature(instrument_temp)
• Filter Temperature(filter_temp)
• Repetition Rate, or Trigger Frequency of the laser(pulse_rep)
• Detector Temperature(detector_temp)
• base time(base_time)
• Laser output energy per pulse(energy_monitor)
• Dummy altitude for Zeb(alt)
• Voltage level which operates the energy monitor(voltage_15)
• GPS raw data filename(filename)
• lon(lon)
• lat(lat)
• Time offset of tweaks from base_time(time_offset)

TWP/MPL/C1 - Missing data

Data are missing and unrecoverable.

• Voltage level which operates the A_D card and the detector(voltage_5)
• Laser Temperature(laser_temp)
• Voltage level which operates the thermistor(voltage_10)
• Preliminary cloud base height above ground level(cbh)
• Aerosol backscatter coefficient at 355 nm(backscatter)
• Number of laser shots recorded(shots_summed)
• Background Signal(background_signal)
• Instrument Temperature(instrument_temp)
• Filter Temperature(filter_temp)
• Repetition Rate, or Trigger Frequency of the laser(pulse_rep)
• Detector Temperature(detector_temp)
• base time(base_time)
• Laser output energy per pulse(energy_monitor)
• Dummy altitude for Zeb(alt)
• Voltage level which operates the energy monitor(voltage_15)
• GPS raw data filename(filename)
• lon(lon)
• lat(lat)
• Time offset of tweaks from base_time(time_offset)

TWP/C1 - Incorrect elevation reported in Manus Data

Bill Clements reports we have been using 6m MSL as the station elevation of Momote 
(Manus).  This was based on information posted near the station barometer in the Momote Weather 
Service Office.  It turns out that the official WMO station elevation for Momote is 4m 
MSL and the upper air elevation is 5m MSL.

All Manus instruments except the sonde station are at 4m MSL. The sonde launching station 
is at 5m MSL.

• Dummy altitude for Zeb(alt)

• Dummy altitude for Zeb(alt)

• Dummy altitude for Zeb(alt)

TWP/MPL/C1 - SunShade timing problem

For an unknown reason, the sun shade was dropping for less then 10 minutes during the 
night at about 19:00 UTC between Dec 14, 2003 and Feb 17, 2004.  Data taken during that ten 
minute interval is not looking at the sky and should be considered as though it were 
missing.

This is a fairly small effect.  Data users can simply average across the interval or block 
the records as "missing".

• Laser Temperature(laser_temp)
• Aerosol backscatter coefficient at 355 nm(backscatter)
• Filter Temperature(filter_temp)
• Background Signal(background_signal)
• Detector Temperature(detector_temp)
• Dummy altitude for Zeb(alt)
• GPS raw data filename(filename)
• lon(lon)
• Time offset of tweaks from base_time(time_offset)
• Voltage level which operates the A_D card and the detector(voltage_5)
• Voltage level which operates the thermistor(voltage_10)
• Preliminary cloud base height above ground level(cbh)
• Number of laser shots recorded(shots_summed)
• Instrument Temperature(instrument_temp)
• Repetition Rate, or Trigger Frequency of the laser(pulse_rep)
• base time(base_time)
• Laser output energy per pulse(energy_monitor)
• Voltage level which operates the energy monitor(voltage_15)
• lat(lat)

• null(Raw data stream - documentation not supported)

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

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

TWP/MPL/C1 - SP laser diode supply failed

The Spectra Physics laser diode supply failed on March 2, 2004.  A replacement was 
installed April 18. 

Any data between these dates is worthless.

• Laser Temperature(laser_temp)
• Aerosol backscatter coefficient at 355 nm(backscatter)
• Filter Temperature(filter_temp)
• Background Signal(background_signal)
• Detector Temperature(detector_temp)
• Dummy altitude for Zeb(alt)
• GPS raw data filename(filename)
• lon(lon)
• Time offset of tweaks from base_time(time_offset)
• Voltage level which operates the A_D card and the detector(voltage_5)
• Voltage level which operates the thermistor(voltage_10)
• Preliminary cloud base height above ground level(cbh)
• Number of laser shots recorded(shots_summed)
• Instrument Temperature(instrument_temp)
• Repetition Rate, or Trigger Frequency of the laser(pulse_rep)
• base time(base_time)
• Laser output energy per pulse(energy_monitor)
• Voltage level which operates the energy monitor(voltage_15)
• lat(lat)

• null(Raw data stream - documentation not supported)

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

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

TWP/MPL/C1 - energy monitor spikes

The energy monitor spiked to abnormal values, from 2 up to 25 microjoules per pulse. At 
the beginning, it was only a few intermittent spikes, but the spikes became more frequent. 
Most of June does not show a spiky energy monitor. On June 28-30, July 1-10 a diurnal 
pattern shows up. On July 12-13 it abruptly goes away and returns July 14-16 for 24hrs. Then 
abruptly stops again 17-19. Except for the 12th, the last changes occurred at 00:00 UTC 
suggesting a piece of equipment is turning on and off. I do not know why a noisy energy 
monitor would have a day/night or 00:00UTC dependence.

• Laser output energy per pulse(energy_monitor)

• null(Raw data stream - documentation not supported)

TWP/MPL/C1 - 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/C1 - Energy monitor values are erroneous

Energy monitor values should not be used to normalization the backscatter profiles. A 
problem with the energy monitor electronics forced the value to maximum. The problem was 
corrected.

• Laser output energy per pulse(energy_monitor)

• null(Raw data stream - documentation not supported)

TWP/MPL/C1 - Time stamps are incorrect.

The computer was experiencing time synchronization problems. The time stamp for the data 
is incorrect. The synchronization continued to get worse throughout the period.  Secondary 
results of the sync problem are data gaps. The problem exhibited itself with data gaps 
at the end of every hour. As the computer continued to get further out of sync, the 
duration of the data gaps increased.

The error in time synchronization can be corrected by comparing the MPL data with another 
instrument such as the ceilometers or MMCR. The error in time can be determined by 
looking for identical cloud structure. Then shift the MPL data in time to match the other 
instruments. Remember the error is not constant; it continues to get worst throughout the period.

• Laser Temperature(laser_temp)
• Voltage level which operates the thermistor(voltage_10)
• Assumed zero-range bin number\(assumed_zero_range_bin)
• Number of laser shots recorded(shots_summed)
• Background Signal(background_signal)
• Instrument Temperature(instrument_temp)
• Filter Temperature(filter_temp)
• 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)
• base time(base_time)
• Detector Temperature(detector_temp)
• Preliminary cloud base height(preliminary_cbh)
• Laser output energy per pulse(energy_monitor)
• time(time)
• Voltage level which operates the energy monitor(voltage_15)
• Attenuated backscatter(detector_counts)
• Voltage level which operates the A/D card and the detector(voltage_05)
• Time in nanoseconds for each range bin of multichannel scalar card.(range_bin_time)
• Time offset of tweaks from base_time(time_offset)

• null(Raw data stream - documentation not supported)

TWP/MPL/C1 - 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)

TWP/MPL/C1 - Data dropouts

Data dropouts occurred during this period. Problem ended when MPL computer was rebooted.

• Background Signal(background_signal)
• Angle of orientation with respect to true geographic north(tranceiver_azimuth_angle)
• range(range)
• Array of heights for the range gates(height)
• Detector Temperature(detector_temp)
• Dummy altitude for Zeb(alt)
• required to correct raw counts for detector deadtime prior to all other
  corrections.(deadtime_correction)
• Amount of time the actual laser pulse lags behind the sync trigger(laser_sync_offset)
• GPS raw data filename(filename)
• lon(lon)
• Attenuated backscatter(detector_counts)
• Maximum altitude retrieved from multichannel scalar card.(max_altitude)
• Voltage level which operates the thermistor(voltage_10)
• Preliminary cloud base height above ground level(cbh)
• Repetition Rate, or Trigger Frequency of the laser(pulse_rep)
• Preliminary cloud base height(preliminary_cbh)
• Voltage level which operates the energy monitor(voltage_15)
• value represents date of last configuration change as yyyymmdd(property)
• lat(lat)
• Angle of inclination with respect to horizontal(tranceiver_altitude_angle)
• Number of laser pulses summed during measurement interval(shots_sum)
• Laser Temperature(laser_temp)
• Aerosol backscatter coefficient at 355 nm(backscatter)
• Filter Temperature(filter_temp)
• time(time)
• Sum of raw backscatter counts per bin prior to ANY corrections.(total_counts)
• Distance from leading edge of first range bin to the center of each bin .(range_bins)
• Repetition rate, or Trigger Frequency of the laser(trigger_freq)
• Time offset of tweaks from base_time(time_offset)
• Voltage level which operates the A_D card and the detector(voltage_5)
• Width of range-bins calculated from range_bin_time(range_bin_width)
• Assumed zero-range bin number\(assumed_zero_range_bin)
• Number of laser shots recorded(shots_summed)
• Instrument Temperature(instrument_temp)
• effective range offset due to poor sync between laser firing and A/D trigger.(range_offset)
• base time(base_time)
• Laser output energy per pulse(energy_monitor)
• Amount of time the scalar lags behind the sync trigger(scalar_sync_offset)
• Amount of time laser pulse lags behind the scalar trigger(laser_scalar_sync_offset)
• Voltage level which operates the A/D card and the detector(voltage_05)
• Time in nanoseconds for each range bin of multichannel scalar card.(range_bin_time)

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

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