NSA/MPL/C1 - Laser Q-Switch Problem

At about 22:52 UTC on 2004/01/19, the NSA MPL appears to have suffered a temporary failure 
of the laser Q-Switch.  This results in a complete loss of lidar data immediately 
thereafter.  The problem was resolved (at least for the time being) by disconnecting and 
reconnecting the Q-Switch cable on 2004/01/24 at about 00:16 UTC.  Data after this time appears 
good.

• Voltage level which operates the thermistor(voltage_10)
• Distance from leading edge of first range bin to the center of each bin .(range_bins)
• Maximum altitude retrieved from multichannel scalar card.(max_altitude)
• range(range)
• Laser output energy per pulse(energy_monitor)
• Array of heights for the range gates(height)
• base time(base_time)
• effective range offset due to poor sync between laser firing and A/D trigger.(range_offset)
• Number of laser shots recorded(shots_summed)
• Instrument Temperature(instrument_temp)
• Background Signal(background_signal)
• Filter Temperature(filter_temp)
• lon(lon)
• time(time)
• Time in nanoseconds for each range bin of multichannel scalar card.(range_bin_time)
• Voltage level which operates the A/D card and the detector(voltage_05)
• Detector Temperature(detector_temp)
• Laser Temperature(laser_temp)
• Voltage level which operates the energy monitor(voltage_15)
• Preliminary cloud base height(preliminary_cbh)
• Attenuated backscatter(detector_counts)
• Repetition Rate, or Trigger Frequency of the laser(pulse_rep)
• lat(lat)
• Time offset of tweaks from base_time(time_offset)
• Width of range-bins calculated from range_bin_time(range_bin_width)
• Dummy altitude for Zeb(alt)

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

• null(Raw data stream - documentation not supported)

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

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

NSA/MPL/C1 - MPL clock drift

The MPL PC clock was noted to be off (slow) by more than an hour over a several day 
period.  It has previously been noted that the time synchronization program "D-4" fails to 
update the PC clock under certain circumstances.  As a result, the program "D-4" was replaced 
by "AboutTime" on 2/5/2004.  

The specifics of this problem are not well understood.  It turns out that the instrument 
has TWO clocks on the instrument computer display - one being displayed by the MPL 
software and the other being the PC clock displayed in the lower right-hand corner of the 
screen. The MPL software clock was the one that is noted on daily rounds and was never off by 
any amount. Apparently the only clock that was off was the computer clock.

What is clear is that between the time the MPL computer was installed on 11-11-2003 and 
the CM log on 1-06-2004 the MPL clock exhibited a discrepancy of over 1 hour and 20 
minutes.  What is not clear is whether this clock discrepancy was also applied to the data time 
stamps.  Furthermore, seven days later the MPL clock exhibited only a 1.77 second drift.  
Not exceptional at all, and not in line with the previous discrepancy of more than 4800 
seconds over a span of 57 days.

Attempts to identify gradual correctible clock drift in the MPL data were not successful.  
As a worst-case scenario, the MPL data may be inappropriately time-stamped by as much a 
1 hour 20 minutes and 41 seconds slow relative to UTC between the dates of 2003-11-11 and 
2004-01-06.  After this time until 2004-02-05 time synchronization was maintained within 
a few seconds a day with local observer assistance.

• time(time)
• Time offset of tweaks from base_time(time_offset)
• base time(base_time)

• Time offset of tweaks from base_time(time_offset)
• base time(base_time)
• time(time)