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)