Data Quality Reports for Session: 104347 User: cj_flynn Completed: 02/17/2007


TABLE OF CONTENTS

DQR IDSubjectData Streams Affected
D050215.5NSA/MPL/C1 - MPL clock driftnsamplC1.a1, nsamplpsC1.a0


DQRID : D050215.5
Start DateStart TimeEnd DateEnd Time
11/11/2003000002/05/20040000
Subject:
NSA/MPL/C1 - MPL clock drift
DataStreams:nsamplC1.a1, nsamplpsC1.a0
Description:
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.
Measurements:nsamplpsC1.a0:
  • Time offset from midnight of date of file. For CO data, this is identical to
    time_offset and is included for compatibility.(time)
  • Time offset of tweaks from base_time(time_offset)
  • Time offset from base_time(base_time)

nsamplC1.a1:
  • Time offset of tweaks from base_time(time_offset)
  • Time offset from base_time(base_time)
  • Time offset from midnight of date of file. For CO data, this is identical to
    time_offset and is included for compatibility.(time)


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