[IGSSTATION-44]: update of day-boundary clock jump analysis

Jim Ray jray at bipm.org
Tue Jun 15 05:08:06 PDT 2004


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IGS Station Mail          15 Jun 08:41:38 PDT 2004      Message Number 44
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Author: Jim Ray

The discontinuity in estimated station clock values at the
boundaries between 1-day arcs is a sensitive measure of the
average pseudorange (code) accuracy averaged over 24-hr
periods.  Ken Senior and I previously described how this can
be used to assess station performance and we reported results
for 30 IGS stations over the ~460 days after Oct 2000.  Our
paper in Metrologia (40(3), S270-S288, 2003) is available
electronically at:
http://www.bipm.org/static/gpst/refs/raysenior-metrologia.pdf

I have updated the day-boundary clock jump analysis using data
available through the end of last week, up to ~1310 days.  The
RMS of the day jumps for each station equipped with an H-maser
clock is given in the table below.  (Other types of clocks are
not sufficiently stable for this test.)  Unfortunately, several
stations no longer use masers (and log files are incorrect).

The editing and processing criteria are the same as our earlier
analysis.  The maximum data gap at the day boundary is 30 min
(typically 5 min), so the effect of any instability in the
H-maser standard itself should be negligible.  Since the RMS
statistics are for the differences between pairs of independent
days, each daily accuracy estimate should be smaller by the
factor 1/sqrt(2).

Of particular note is the very large dispersion in RMS
performance, about one order of magnitude, which reflects the
wide range in code performance among IGS stations.  This in
turn shows the vast variation in multipath environments, both
external to the antenna and internal to the GPS instrumentation.
In some cases the performance has varied markedly with time,
sometimes for known reasons that can be correlated with changes
reported in the site logs.

Plots and data files are available upon request.


      RMS clk
Site  jump/ps  Remarks
----  -------  ----------------------------------------------
ONSA   149.49  excellent
BREW   151.89  excellent
OPMT   158.39  new station, so very limited data
BRUS   164.82  after changes in summer 2003 improved to 118 ps!
MAD2   170.19  very limited data, so RMS is not reliable
WTZR   189.13  

GODE   204.59  
USN1   225.03  
WSRT   226.73  slight degradation since summer 2003
KHAJ   232.90  limited data
CRO1   235.90  maser no longer used
USUD   265.84  maser no longer used
NPLD   267.68  
TID*   269.00  appears improved since summer 2003
YEBE   270.70  
GOL2   271.23  almost no data, so RMS is not reliable
AMC2   282.58  improved after ant/rx changes in June 2002
SPT0   286.38  
WES2   296.02  

PIE1   305.25  improved since Oct 2002 (rx change)
STJO   334.01  
USNO   353.97  appears worse since spring 2003
IRKT   359.15  
NYAL   363.11  much better than NYA1 recently
NLIB   367.83  
MATE   388.62  significant time variations; recently better

KOKB   460.19  large degradation before recent ant/cable changes
FAIR   477.94  somewhat improves since summer 2003
DRAO   521.78  
YELL   563.76  large seasonal variations, much worse in winters
ALBH   587.13  after Sept 2002 greatly improved to 97 ps!

HOB2   631.46  variations correlated with station changes
MEDI   703.24  maser no longer used ???
FORT   705.50  
NYA1   749.95  large degradation since summer 2003

ALGO   877.47  large seasonal variations, much worse in winters
NRC1   935.94  large seasonal variations, much worse in winters
METS  1064.80  maser no longer used





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