[IGSREPORT-3124] revised LODR comparisons

[Jim]

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IGS Electronic Report    Tue Nov  5  9:31:47 PST 1996      Message Number 3124
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Author: Jim Ray, NOAA Geosciences Lab
Subject: revised LODR comparisons

To: IGS ACs, IERS/CB, USNO, IGS Reports

Revised LODR comparison results
-------------------------------
The solution procedures used for the n9609 VLBI series have been revised
by USNO.  Mainly, the constraints applied to the tropospheric rate of change
parameter have been tightened for the brief, quasi-daily UT1 sessions.
Among other things, this causes the formal errors of the derived LODR
series to be smaller than for the previous n9609 series.

Qualitatively, the conclusions of my message last week still hold.  However,
the statistical results are changed, with uniformally smaller wtd. wrms
differences.  This is especially true for the most recent 52-day period
where the differences compared to VLBI now range between 42 and 62 usec/day
(versus 51 to 69 previously reported).  Apparently, increased error in
recent VLBI results was responsible for much of the observed increased in
recent LODR scatter for the best IGS solutions, contrary to my earlier
assertion.  The operation of the daily UT1 sessions has been less
homogeneous than normal lately, which could possibly contribute somewhat
to the recent increased scatter.


                             REVISED (05 Nov 96)            
           ----- wtd mean/wtd rms LODR differences wrt VLBI ----
           -----            (all units usec/day)            ----
   most 
   recent                 EMR                                      VLBI
   # days   COD    EMR    UT1    ESA*   GFZ    JPL    NGS    SIO    ERR
   --------------------------------------------------------------------
   826    -22.9  -12.3    4.9  -38.6  -27.0  -10.9         -63.0   32.1
           38.4   61.4   35.8   65.5   57.9   59.1          86.0    9.5

   413    -23.3   -1.6    4.0  -12.8  -22.1    2.5    5.7   -5.3   32.9
           38.4   57.2   36.5   53.1   54.3   55.3   54.8   49.3   10.5

   207    -28.9  -18.3    1.0  -19.8  -31.2    4.7   -6.6   -8.2   34.5
           41.7   59.8   41.3   54.3   52.4   68.8   53.0   55.4   11.3

   103    -21.6   -3.9    2.4   -8.0  -17.5   29.4   -9.5   -4.6   33.7
           46.4   54.2   40.9   51.9   43.2   73.5   51.7   55.7   11.0

    52    -22.2   -2.6    3.0  -21.6  -28.4    0.8  -26.0  -17.2   32.6
           50.9   55.0   44.7   54.4   42.4   62.3   52.7   58.8   11.0
   --------------------------------------------------------------------
   Note: Considers IGS LOD values from MJD 49536.5 (03 Jul 94), in the
	 longest instance, to MJD 50361.5 (05 Oct 96).
   * After deletion of LOD value from ESA for MJD 50313.5; including
     that day would give a wtd. mean difference of -41.2 usec/day and
     a wrms of 161.4 usec/day for the most recent 52 days.


Revised postscript plots have been posted at ftp://ray.grdl.noaa.gov/pub/.


[Mailed From: Jim Ray (NOAA 301-713-2850) <jimr at ray.grdl.noaa.gov>]