TWP/MPL/C2 - Power Oscillation

There is an oscillation that shows up in the reflected power and the power monitor.  This 
oscillation shows up clearly whenever there is an absence of low (< ~5 km) clouds. Cloud 
return signals tend to be much larger than the level of this oscillation; however, it may 
introduce problems for studying aerosol distributions.  The end date of this DQR is 
artificial in that this is as far as the QC went.

• energy_monitor
• Backscatter(backscatter)

TWP/C2/MPL Detector

The MPL detector failed and was shut down.

• range_bin_time
• pulse_rep
• lon
• voltage_05
• base_time
• range_offset
• property
• shots_summed
• shots_sum
• instrument_temp
• time_offset
• Pressure, associated geometric height, at altitude, NGM model output(height)
• lat
• Backscatter(backscatter)
• filter_temp
• laser_scalar_sync_offset
• transceiver_azimuth_angle
• detector_temp
• range_bins
• deadtime_correction
• time
• total_counts
• energy_monitor
• transceiver_altitude_angle
• Preliminary cloud base height above ground level(preliminary_cbh)
• alt
• laser_temp
• scalar_sync_offset
• background_signal
• range
• voltage_15
• voltage_10
• range_bin_width
• max_altitude
• trigger_freq
• laser_sync_offset

• Raw data stream - documentation not supported

• base_time
• Heights
• time_offset
• MPL Cloth et al. Algorithm Significance Mask(SigniMaskMplCloth)

• MPL Cloth et al. Algorithm Cloud Mask(CloudMaskMplCloth)
• Heights
• base_time
• time_offset

• energy_monitor
• shots_summed
• cloud_top_attenuation_flag
• lat
• base_time
• instrument_temp
• baseline_update_time
• time_offset
• pulse_rep
• background_signal
• cloud_mask_1
• cloud_mask_2
• alt
• Cloud base height(cloud_base_height)
• lon
• Backscatter(backscatter)
• Pressure, associated geometric height, at altitude, NGM model output(height)
• Cloud top height(cloud_top_height)
• detector_temp
• laser_temp
• random_error

TWP/MPL/C2 - Nauru MPL Laser Diode accidentally off

The emission from the laser diode supply was accidentally off.  The Instrument
Mentor, Connor Flynn, called Nauru directly and had them turn the laser emission
back on.  Backscatter and cloud base data during the period between 
2000-11-11 00:00 GMT and 2000-11-13 22:00 GMT should be regarded as bad 
or incorrect while background light data and local temperature values are 
acceptable.

• Backscatter(backscatter)
• Preliminary cloud base height above ground level(preliminary_cbh)

TWP/MPL/C2 - Laser emission accidentally turned off

Shortly after 00:00 GMT on 11/11/00, the MPL Energy Monitor value dropped
abruptly to zero.  At about 22:00 GMT on 11/13/00, the remote handset for
the laser diode supply was used to turn the laser back on.

• range_bin_time
• pulse_rep
• lon
• voltage_05
• base_time
• range_offset
• property
• shots_summed
• shots_sum
• instrument_temp
• time_offset
• Pressure, associated geometric height, at altitude, NGM model output(height)
• lat
• Backscatter(backscatter)
• filter_temp
• laser_scalar_sync_offset
• transceiver_azimuth_angle
• detector_temp
• range_bins
• deadtime_correction
• time
• total_counts
• energy_monitor
• transceiver_altitude_angle
• Preliminary cloud base height above ground level(preliminary_cbh)
• alt
• laser_temp
• scalar_sync_offset
• background_signal
• range
• voltage_15
• voltage_10
• range_bin_width
• max_altitude
• trigger_freq
• laser_sync_offset

• Raw data stream - documentation not supported

• base_time
• Heights
• time_offset
• MPL Cloth et al. Algorithm Significance Mask(SigniMaskMplCloth)

• MPL Cloth et al. Algorithm Cloud Mask(CloudMaskMplCloth)
• Heights
• base_time
• time_offset

• alt
• Preliminary cloud base height above ground level(cbh)
• lon
• time_offset
• lat
• base_time

• energy_monitor
• shots_summed
• cloud_top_attenuation_flag
• lat
• base_time
• instrument_temp
• baseline_update_time
• time_offset
• pulse_rep
• background_signal
• cloud_mask_1
• cloud_mask_2
• alt
• Cloud base height(cloud_base_height)
• lon
• Backscatter(backscatter)
• Pressure, associated geometric height, at altitude, NGM model output(height)
• Cloud top height(cloud_top_height)
• detector_temp
• laser_temp
• random_error

• Raw data stream - documentation not supported

TWP/MPL/C1 - Missing data

Data are missing and unrecoverable.

• voltage_05
• range_offset
• property
• Backscatter(backscatter)
• shots_sum
• time_offset
• range
• voltage_5
• max_altitude
• scalar_sync_offset
• deadtime_correction
• range_bin_width
• Preliminary cloud base height above ground level(preliminary_cbh)
• range_bins
• Preliminary cloud base height above ground level(cbh)
• detector_counts
• shots_summed
• tranceiver_altitude_angle
• lat
• range_bin_time
• laser_sync_offset
• voltage_10
• pulse_rep
• laser_temp
• total_counts
• background_signal
• alt
• voltage_15
• filename
• lon
• instrument_temp
• detector_temp
• Pressure, associated geometric height, at altitude, NGM model output(height)
• filter_temp
• assumed_zero_range_bin
• time
• base_time
• tranceiver_azimuth_angle
• trigger_freq
• laser_scalar_sync_offset
• energy_monitor

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

• Backscatter(backscatter)

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.

• alt

• alt

• alt

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

• range_bin_time
• time
• pulse_rep
• total_counts
• voltage_05
• lon
• energy_monitor
• transceiver_altitude_angle
• base_time
• range_offset
• Preliminary cloud base height above ground level(preliminary_cbh)
• property
• alt
• laser_temp
• scalar_sync_offset
• shots_summed
• shots_sum
• background_signal
• instrument_temp
• range
• time_offset
• Pressure, associated geometric height, at altitude, NGM model output(height)
• lat
• voltage_15
• Backscatter(backscatter)
• range_bin_width
• voltage_10
• filter_temp
• laser_scalar_sync_offset
• max_altitude
• trigger_freq
• transceiver_azimuth_angle
• detector_temp
• laser_sync_offset
• deadtime_correction
• range_bins

• Raw data stream - documentation not supported

• MPL Cloth et al. Algorithm Significance Mask(SigniMaskMplCloth)
• base_time
• Heights
• time_offset

• MPL Cloth et al. Algorithm Cloud Mask(CloudMaskMplCloth)
• time_offset
• Heights
• base_time

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.

• range_bin_time
• pulse_rep
• lon
• voltage_05
• base_time
• range_offset
• property
• shots_summed
• shots_sum
• instrument_temp
• time_offset
• Pressure, associated geometric height, at altitude, NGM model output(height)
• lat
• Backscatter(backscatter)
• filter_temp
• laser_scalar_sync_offset
• transceiver_azimuth_angle
• detector_temp
• range_bins
• deadtime_correction
• time
• total_counts
• energy_monitor
• transceiver_altitude_angle
• Preliminary cloud base height above ground level(preliminary_cbh)
• alt
• laser_temp
• scalar_sync_offset
• background_signal
• range
• voltage_15
• voltage_10
• range_bin_width
• max_altitude
• trigger_freq
• laser_sync_offset

• Raw data stream - documentation not supported

• base_time
• Heights
• time_offset
• MPL Cloth et al. Algorithm Significance Mask(SigniMaskMplCloth)

• MPL Cloth et al. Algorithm Cloud Mask(CloudMaskMplCloth)
• Heights
• base_time
• time_offset

• alt
• Preliminary cloud base height above ground level(cbh)
• lon
• time_offset
• lat
• base_time

• energy_monitor
• shots_summed
• cloud_top_attenuation_flag
• lat
• base_time
• instrument_temp
• baseline_update_time
• time_offset
• pulse_rep
• background_signal
• cloud_mask_1
• cloud_mask_2
• alt
• Cloud base height(cloud_base_height)
• lon
• Backscatter(backscatter)
• Pressure, associated geometric height, at altitude, NGM model output(height)
• Cloud top height(cloud_top_height)
• detector_temp
• laser_temp
• random_error

• Raw data stream - documentation not supported

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.

• range_bin_time
• time
• pulse_rep
• total_counts
• voltage_05
• lon
• energy_monitor
• transceiver_altitude_angle
• base_time
• range_offset
• Preliminary cloud base height above ground level(preliminary_cbh)
• property
• alt
• laser_temp
• scalar_sync_offset
• shots_summed
• shots_sum
• background_signal
• instrument_temp
• range
• time_offset
• Pressure, associated geometric height, at altitude, NGM model output(height)
• lat
• voltage_15
• Backscatter(backscatter)
• range_bin_width
• voltage_10
• filter_temp
• laser_scalar_sync_offset
• max_altitude
• trigger_freq
• transceiver_azimuth_angle
• detector_temp
• laser_sync_offset
• deadtime_correction
• range_bins

• Raw data stream - documentation not supported

• MPL Cloth et al. Algorithm Significance Mask(SigniMaskMplCloth)
• base_time
• Heights
• time_offset

• MPL Cloth et al. Algorithm Cloud Mask(CloudMaskMplCloth)
• time_offset
• Heights
• base_time

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".

• Backscatter(backscatter)
• time_offset
• voltage_5
• Preliminary cloud base height above ground level(cbh)
• shots_summed
• lat
• voltage_10
• pulse_rep
• laser_temp
• alt
• background_signal
• voltage_15
• filename
• lon
• instrument_temp
• detector_temp
• filter_temp
• base_time
• energy_monitor

• MPL Cloth et al. Algorithm Cloud Mask(CloudMaskMplCloth)
• Heights
• base_time
• time_offset

• Raw data stream - documentation not supported

• base_time
• time_offset
• MPL Cloth et al. Algorithm Significance Mask(SigniMaskMplCloth)
• Heights

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.

• Backscatter(backscatter)
• time_offset
• voltage_5
• Preliminary cloud base height above ground level(cbh)
• shots_summed
• lat
• voltage_10
• pulse_rep
• laser_temp
• alt
• background_signal
• voltage_15
• filename
• lon
• instrument_temp
• detector_temp
• filter_temp
• base_time
• energy_monitor

• MPL Cloth et al. Algorithm Cloud Mask(CloudMaskMplCloth)
• Heights
• base_time
• time_offset

• Raw data stream - documentation not supported

• base_time
• time_offset
• MPL Cloth et al. Algorithm Significance Mask(SigniMaskMplCloth)
• Heights

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.

• energy_monitor

• 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

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

TWP/MPL/C3 - 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

TWP/MPL/C3 - Temporary laser failure

No backscatter information is in the data. The backscatter data in the files during this 
time is solar background information only. 

The laser turned it's self off, reason: unknown. A power cycle of the entire system 
corrected the problem.

• Raw data stream - documentation not supported

• Preliminary cloud base height above ground level(preliminary_cbh)
• detector_counts

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.

• energy_monitor

• Raw data stream - documentation not supported

TWP/MPL/C3 - Backscatter profiles are inaccurate due to computer HD corruption.

The data shows a consistent cloud deck at 7.5km with what appears to be a duplication of 
the data from ground zero. The temperature and energy monitor values are also affected. 
The computer was found with multiple corruption problems. These corruptions may have cause 
the ghost data at 7.5km.  A chkdsk was performed which appears to have corrected the 
problem.

• Raw data stream - documentation not supported

• background_signal
• instrument_temp
• energy_monitor
• laser_temp
• detector_temp
• Preliminary cloud base height above ground level(preliminary_cbh)
• detector_counts

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.

• voltage_05
• voltage_10
• range_offset
• pulse_rep
• laser_temp
• background_signal
• time_offset
• voltage_15
• instrument_temp
• detector_temp
• filter_temp
• assumed_zero_range_bin
• Preliminary cloud base height above ground level(preliminary_cbh)
• time
• base_time
• detector_counts
• shots_summed
• range_bin_time
• energy_monitor

• 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.

• detector_counts

TWP/MPL/C3 - Missing data due to instrument removal

The instrument was removed from this site to replace a failed instrument at TWP-C2 Nauru.

• Raw data stream - documentation not supported

• range
• voltage_10
• Pressure, associated geometric height, at altitude, NGM model output(height)
• voltage_15
• range_bin_width
• time_offset
• detector_counts
• assumed_zero_range_bin
• lat
• base_time
• shots_summed
• laser_temp
• range_bin_time
• time
• detector_temp
• range_offset
• instrument_temp
• background_signal
• alt
• lon
• energy_monitor
• pulse_rep
• max_altitude
• Preliminary cloud base height above ground level(preliminary_cbh)
• range_bins
• filter_temp
• voltage_05

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.

• detector_counts

• Raw data stream - documentation not supported

TWP/MPL/C2 - Detector on instrument failed.

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

• detector_counts

• Raw data stream - documentation not supported

TWP/MPL/C2 - Missing data

The MPL was turned off due to a dead detector.

• range_bin_time
• time
• pulse_rep
• total_counts
• voltage_05
• lon
• energy_monitor
• transceiver_altitude_angle
• base_time
• range_offset
• Preliminary cloud base height above ground level(preliminary_cbh)
• detector_counts
• property
• alt
• assumed_zero_range_bin
• laser_temp
• scalar_sync_offset
• shots_summed
• shots_sum
• background_signal
• instrument_temp
• range
• time_offset
• Pressure, associated geometric height, at altitude, NGM model output(height)
• lat
• voltage_15
• Backscatter(backscatter)
• range_bin_width
• voltage_10
• filter_temp
• laser_scalar_sync_offset
• max_altitude
• trigger_freq
• transceiver_azimuth_angle
• detector_temp
• laser_sync_offset
• deadtime_correction
• range_bins

• Raw data stream - documentation not supported

TWP/MPL/C1 - Data dropouts

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

• Backscatter(backscatter)
• range
• max_altitude
• scalar_sync_offset
• deadtime_correction
• range_bins
• Preliminary cloud base height above ground level(preliminary_cbh)
• range_bin_width
• Preliminary cloud base height above ground level(cbh)
• tranceiver_altitude_angle
• laser_sync_offset
• voltage_10
• laser_temp
• background_signal
• voltage_15
• instrument_temp
• assumed_zero_range_bin
• trigger_freq
• laser_scalar_sync_offset
• range_offset
• voltage_05
• property
• time_offset
• shots_sum
• voltage_5
• detector_counts
• shots_summed
• lat
• range_bin_time
• pulse_rep
• total_counts
• alt
• lon
• filename
• Pressure, associated geometric height, at altitude, NGM model output(height)
• detector_temp
• filter_temp
• time
• base_time
• tranceiver_azimuth_angle
• energy_monitor

• Heights
• base_time
• time_offset
• MPL Cloth et al. Algorithm Cloud Mask(CloudMaskMplCloth)

• time_offset
• base_time
• MPL Cloth et al. Algorithm Significance Mask(SigniMaskMplCloth)
• Heights

TWP/MPL/C2 - Reprocess: Incorrect longitude and altitude reported

The longitude of the MPL instrument is reported as -166.916.  The correct longitude is 
+166.916.

The altitude of the MPL instrument is reported as 7.2.  The correct altitude is 7.1 M.

These data will be reprocessed at a low priority.

• alt
• lon

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.

• detector_counts

TWP/MPL/C3 - 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.

• detector_counts