Subject: [IGSREPORT-0832] IGS Final Orbit Comb(730)
From: Analysis Centres Coordinator / Geodetic Survey of Canada
Date: Thu, 10 Mar 1994 11:25:10 PST

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IGS Electronic Report    Thu Mar 10 11:25:10 PST 1994      Message Number 0832
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Author: Analysis Centres Coordinator / Geodetic Survey of Canada
Subject: IGS Final Orbit Comb(730)

IGS Final Orbit Combination Week 0730             (Jan 02, 1994 - Jan 08, 1994)

Contacts: F. Lahaye ([email-masked]), J. Kouba ([email-masked])

COMBINATION STRATEGY:

Each centre ephemeris and satellite clock corrections are first transformed to
common reference. The differences between each centre X and Y pole solutions
and the IERS Bulletin B are used to rotate the corresponding ephemeris. If the
pole solution is not available for a particular centre, no such rotations are
applied. For each centre, a clock offset and drift, common for all satellites,
are estimated with respect to broadcast clock corrections. These offsets and
drifts are used to align each centre satellite clock corrections to GPS time.
The resulting ephemerides and clock corrections are then combined as weighted
averages computed over all centres. Each centre is given a position weight and
a clock weight. The position weights are computed from the absolute deviation
to the unweighted average orbit after the estimation of a 7-parameter Helmert
transformation. The clock weights are computed from the absolute deviation to
the unweighted average clock corrections after estimation of offsets and
drifts. The above estimations are performed using the L1-norm robust scheme.
Each centre ephemeris are also evaluated individually and independently from
the orbit combination by using week long arcs. The ERP used in this evaluation
are those submitted by the respective centres supplemented with IERS Bulletin A
UT1-UTC values when they are not supplied.
Like the clock solutions broadcast in the navigation message, the combined
satellite clocks are corrected for the periodical relativistic correction
(see e.g. GPS interface Control document ICD-GPS-200, p.73):

                              -2*(X.V)/c,

where X and V are the sv state and velocity vectors and c is the speed of
light. Also for compatibility, no satellite L1/L2 delay calibration should be
applied.

SOFTWARE:

The weighted average software used was developed by T. Springer and G. Beutler
during 1993. The GPS long arc orbit analysis software used here for individual
centre ephemeris evaluation was developed by Beutler et al. at the Astronomical
Institute of the University of Bern (AIUB). For more details on the orbit
combination and complete references for both software see:

   Beutler, Kouba, Springer, 1993, Combining orbits of the IGS processing
   centres, in IGS Analysis Centre Workshop, October 12-14, Ottawa, pp 19-55.

PRODUCTS GENERATED:

The resulting average ephemeris and clocks are output to daily files in SP3
format. The satellite accuracy codes displayed in the header are based on the
weighted RMS for each satellite. Note that each file contains all the
satellites that appear in any of the centre ephemeris files. If a satellite or
centre was excluded from combination, a note in the REMARKS section of this
report will identify the exclusion and the reason.

The IGS Final Orbit files generated and uploaded into CDDIS @ NASA/GSFC are:

 IGS07300-6.SP3  IGS GPS ephemeris files for days 0-6, week 0730 in SP3 format.
 IGS07307.ERP    Earth rotation parameters (ERP) associated with ephemerides.
 IGS07307.SUM    Complete report.

The old Rapid Service files have been renamed to:

 IGR07300-6.SP3  Rapid Service ephemeris files for days 0-6.
 IGR07307.ERP    Rapid Service earth rotation parameters (ERP).
 IGR07307.SUM    Rapid Service complete report.

REMARKS on IGS Final Orbit Combination:

1. Only the GFZ "exact" clock corrections (one epoch out of two) are included
   in the combination and RMS computation (no "interpolation" values).

2. ESA satellite clock corrections were not incuded in the combination since
   they exhibit systematic effects at the 10 nano-seconds level due to not
   accounting for relativistic effects.

3. The EMR clock corrections were excluded from combination on day 1 (Jan 3)
   due to an unusually large RMS ~ 100 nano-seconds.

4. On day 4 (Jan 6), JPL and GFZ clock are excluded from combination because of
   a clock reset at ALGO. The EMR solution, properly aligned, is provided here.

5. NGS produced solutions for day 4 and 5 (Jan 6 and 7) as well as an EOP file
   for the whole week that were not used in the Rapid Combination.

6. The anomalous NGS solution for PRN01 on day 5 (Jan 7) was not included in
   combination but used in statistics compilation (see Table 2.0730.5 and
   Table 3.0730.5) and long-arc orbit evaluation.

7. Satellite state vector resets in the long-arc orbit evaluation (Table 3):
     PRN17  : Day 1 (Jan 3) @ 00:00 UTC
     PRN04  : Day 2 (Jan 4) @ 00:00 UTC
     PRN23  : Day 3 (Jan 5) @ 00:00 UTC
     PRN05  : Day 6 (Jan 8) @ 00:00 UTC

ORBIT COMBINATION AND EVALUATION STATISTICS:

Most combination statistics are with respect to the combined orbits and consist
of three parts. The first, Table 1, summarizes all statistics for the week. It
contains means and standard deviations over the week of satellite ephemeris and
clock correction transformation parameters for each centre (table 1.0730.a).
It also displays the computed satellite position sigmas for the combined orbits
(table 1.0730.b). The second part, Table 2, contains the complete ephemeris
and clock correction transformation parameters (includes both the apriori and
a posteriori values) for each centre and each day (tables 2.0730.0-6). The
third and final part, Table 3, contains two types of daily RMS for each
satellite and centre, along with the computed satellite position sigmas for the
combined orbits (tables 3.0730.0-6). The first type of satellite RMS is based
on orbit combination and the second RMS type is a result of the 7-day arc
evaluation of each centre ephemerides.
In all tables, the most important statistic which is meaningful for intra
centre/satellite analysis is labeled WRMS. It is a weighted RMS where
normalized weights are based on accuracy codes given in the SP3 files, and
should not be affected by downweighted/problem satellites when acknowledged by
individual centres in their SP3 file.

Table 1: Week 0730 summary.                       (Jan 02, 1994 - Jan 08, 1994)

Table 1.0730.a   GPS week: 0730   MJD: 49354.0-49360.0

         Mean and standard deviations of transformation parameters.
         WRMS - orbit RMS weighted by the SP3 header accuracy codes.
         Units: meters, mas, ppb, nano-sec, nano-sec/day.

CENT|   DX   DY   DZ    RX    RY    RZ  SCL   RMS  WRMS |   TOFT  TDRFT    RMS
----|---------------------------------------------------|---------------------
cod |  .00  .01  .01  1.10   .23   .35   .0   .15   .13 |    1.2   -5.0   74.4
    |  .00  .01  .00   .32   .24   .18   .1             |    4.9    6.4
emr |  .01 -.01 -.01  1.94   .98   .00  -.2   .15   .15 | -109.0  -38.7   41.2
    |  .01  .01  .01   .44   .24   .41   .1             |  106.9   21.8
esa |  .01  .00  .00  1.35   .27  -.99  -.2   .23   .25 |     .0  -33.4   11.9
    |  .02  .01  .01   .40   .20   .51   .2             |   15.0    3.4
gfz | -.04  .00  .03  1.57  2.06  -.31  -.5   .18   .13 |-1880.6  287.7  244.3
    |  .01  .01  .01   .08   .13   .21   .2             |  896.0  754.4
jpl |  .00  .04  .00   .97   .39   .19   .2   .18   .19 |-1765.9  -54.4  391.6
    |  .02  .02  .02   .36   .22   .25   .3             |  805.3   82.7
ngs |  .00 -.02  .00  -.17  1.14   .95  1.8  1.28  1.28 |     .0     .0     .0
    |  .01  .02  .02   .32   .21   .53   .4             |     .0     .0
sio |  .05 -.05 -.07  1.36   .05   .08   .4   .26   .27 |     .0     .0     .0
    |  .01  .02  .01   .31   .91   .19   .4             |     .0     .0

Table 1.0730.b   GPS week : 0730   MJD: 49354.0-49360.0

         Satellite position sigmas for the combined orbits
         (coded in the IGS SP3 orbit files).
         "E" flags eclipsing satellites.
         Units: cm.

              Day of GPS week
 PRN  |   0   1   2   3   4   5   6 |  Remarks
------|-----------------------------|------------------------------------------
   1  |   5   5   7   5  17  12   5 |
   2E |   7   6   5   5   6   6   7 |
   3  |  10   5   6   5   4   5   5 |
   4E |  10  19  26  10  22  10   9 |
   5E |   7   8   7   6   6  11  21 |
   7  |   6   5   5   5   6   7   6 |
   9  |   6  10   5   6   5   8   6 |
  12E |   6   7   5   5   5   6   5 |
  13  |   8   7   7   5   6   7   6 |
  14  |   6   6   6   5   6   5   5 |
  15E |   9   8  10   7   6   7   6 |
  16  |   7   5   6   6   6   6   6 |
  17E |   7   6  20   7   6   8  14 |
  18  |   4   4   3   4   4   4   3 |
  19  |   6   8  15   5   4   5   4 |
  20E |   8   6   7   5   4   8   8 |
  21  |   6   4   3   4   4   5   6 |
  22E |   6   5   5   6   5   6   6 |
  23  |   6   5   7  10   7   7   8 |
  24E |   9  10  11   7   9   8   8 |
  25  |   6   7   7   6   6   6   7 |
  26  |   6   7   6   6   5   9   6 |
  27  |   4   5   4   4   4   3   4 |
  28  |   5   4   4   3   4   4   4 |
  29  |   4   4   3   4   3   4   3 |
  31  |   6   6   7   7   5   8   6 |

For Table 2 and 3, please refer to the complete report (IGS07307.SUM) posted
on CDDIS.