Subject: [IGSMAIL-103] Preliminary look at GPS Earth orientation
From: Dennis McCarthy
Date: 23 SEP 1992 11:49:23

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IGS Electronic Mail       23-SEP-1992 11:49:23       Message Number 103
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                   THIS FILE CONTAINS 2 MESSAGES
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From:     Dennis McCarthy
Subject:  Preliminary look at GPS Earth orientation
          -----------------------------------------

Date:     22 September 1992

An updated look at Earth orientation data submitted to the IERS
follows.  Units are milliseconds of arc for x and y, and
milliseconds of time for UT1-UTC.

Contributor Data Span Points       Mean          Standard Deviation
                                (NEOS-GPS)  
                              x     y   UT1-UTC   x     y   UT1-UTC
U. of Texas  48794.5    62  -0.77 -2.50          1.26  1.89  
             -48863.5

Scripps      48780.5    96  -1.15 -1.62          0.65  0.56
             -48876.5     

U. of Berne  48792.5     8  -1.15  1.19  -0.28   1.52  1.87  0.13 
 (ITRF90)    -48799.5

U. of Berne  48800.5    76  -0.47  0.20  -1.92   0.75  0.94  0.99 
(ITRF91)    -48875.5

JPL          48794.5    69  -1.23 -0.07          0.64  0.90 
             -48870.5

GFZ          48795.0    60  -2.35  -1.81         1.25  1.30
             -48855.5

ESOC         48763.5    79  -1.66  0.54          1.35  2.20
             -48877.5

Plots are available by FAX to anyone interested.

Regards,

Dennis McCarthy
  [email-masked]

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From:     James F. Zumberge
Subject:  JPL analysis report
          -------------------

Submitted by*

J F Zumberge, G Blewitt, M B Heflin, D C Jefferson, F H Webb

all at the Jet Propulsion Laboratory, California Institute of Technology,
Pasadena, CA  91109.
*New dynamic-stochastic orbit estimation strategy was developed 
by Yvonne Vigue, JPL.

The following files have been posted on BODHI (for access to BODHI contact
[email-masked]):

______________________________________________________________________________
filename               contents
______________________________________________________________________________
jpl06617.sum           This text file.
jpl06617.erp           Earth rotation parameters for GPS week 661.
jpl06617.sp1           GPS ephemerides for GPS week 661, sp1 format.
jpl06617.sp3            "       "       "   "   "    " , sp3   "   .
______________________________________________________________________________
Beginning with the Sep 6 analysis and continuing indefinitely, we have enhanced
our parameter estimation strategy by treating the solar radiation pressure
parameters for GPS satellites as stochastic parameters. Prior to Sep 6, our
daily analyses solved for these as constant (over the day) parameters.

Our strategy been changing since our original submission, so we summarize
the current status in the table below. Details on the new orbit strategy are
given below the table.

Description of the JPL rapid service GPS solutions starting Sept 6, 1992
===============================================================================
(1)  Technique:                       GPS (simultaneous, one-way LC and PC data)
(2)  Analysis Center:                 JPL
(3)  Solution identifier:             EPH(JPL)06617
(4)  Software used:                   GIPSY/OASIS-II
(5)  Relativity scale:                Local Earth
(6)  Permanent tide correction:       No
(7)  Tectonic plate model:            ITRF 91 (IGS #90, Boucher and Altamimi)
(8)  Velocity of light                299792458 m/sec
(9)  GM                               3.986004415E+14 m^3/s^2
(10) Reference epoch                  1992.5
(11) Adjusted parameters (all parameters reset every UTC midnight):
                                      Station X, Y, Z except for fiducials:
                                        ALGO,FAIR,HART,KOKB,MADR,TROM,SANT,YAR1
                                      Pole X, Y biases at noon; X and Y rates
                                      UT1R rate
                                      GPS epoch state: X, Y, Z, Vx, Vy, Vz,
                                       estimated as constant; and 3 solar
                                       radiation biases Gx, Gz, and Gy estimated
                                       as a constant plus colored process noise
                                       with 4 hour correlation time. Gx and Gz
                                       are "lumped" (100% correlated).
                                      Zenith tropospheric biases as random walk
                                       process noise
                                      Station and satellite clocks as white
                                       process noise (except that Fairbanks
                                       H-maser is the reference clock);
                                      Carrier phase ambiguities as
                                       real valued (not bias-fixed)
(12) Definition of origin             ITRF91 (IGS #90, Boucher and Altamimi) and
                                       gravity field fixed to GEM-T3.
(13) Definition of orientation         ITRF91 (IGS #90, Boucher and Altamimi)
(14) Constraint for time-evolution    No time evolution (single-day solutions)
===============================================================================

IGS Mail Message 81 (Subject: JPL orbit products) contains the definition
of the body-fixed XYZ coordinate system. Denote by GX and GZ the
dimensionless parameters which scale the ROCK4 model solar radiation
pressure accelerations in the X and Z directions, respectively.
GX and GZ are now modeled as a constant plus a colored noise process.
The constant has an a priori sigma of sqrt(2), while the noise has
steady-state sigma of 10% and a time constant of 4 hours. (GX and GZ
are now assumed 100% correlated.) GY is assumed independent of GX
and GZ, and is also modeled as a constant plus colored noise. The
constant component has a priori sigma 1e-12 km/s^2, while the noise
component has a steady-state sigma of 1e-13 km/s^2 and a 4-hour time
constant. As before, nominal values for each day's satellite epoch
states (including GX, GY, and GZ) come from least-squares fits to the
broadcast ephemeris data.

One consequence of this change in strategy will be an increase in the
formal errors of earth orientation parameters. We expect the new formal
errors will be more realistic. A second consequence may be somewhat higher
(~ 50%) values in the JPL ORBIT REPEATABILITY TABLE, due to larger
uncertainties in extrapolated values of satellite positions. This does not,
of course, imply that the orbit estimates are worse. Tests indicate that
the accuracy of estimates for the Earth center of mass (geocenter) are improved
by a factor of ~5 with this new strategy, leading us to believe that our orbit
accuracy has also improved. (However, be aware that our rapid service
analysis do not estimate the geocenter).

A-S was in effect beginning Sep 12 at 0100 UT to Sep 14 1000 UT. This
submission excludes results from Sep 12.

The motion of PRN14 on Sep 7 and 8, and that of PRN16 on Sep 9-11, are not
well-explained by our model. Data from these days and satellites were heavily
de-weighted in the solutions.

WARNING: PRN14 is poorly modeled on Sep 7 and 8, and PRN16 is poorly modeled
on Sep 9-11. The broadcast ephemerides are recommended for these satellites
and days.

JPL LODR TABLE                               GPS week 661 (1992 Sep 06 - Sep 11)
  MJD       LODR     +/-
          (ms/day)
 48871.5    2.08     0.07
 48872.5    1.73     0.07
 48873.5    1.84     0.07
 48874.5    1.81     0.07
 48875.5    1.95     0.07
 48876.5    1.84     0.07
END LODR TABLE

NOTE: In the following table, UT1R-UTC are the assumed nominal values from
IERS Bulletin-B predicts; estimated LODR values are given in the previous
table. See IGS Mail Message 97 for details.

JPL UTPM TABLE                               GPS week 661 (1992 Sep 06 - Sep 11)
  MJD       X        Y       UT1R-UTC XSIG    YSIG   UTSIG  RMS  XYC  XUC  YUC S
TA SAT PASS
           ''        ''        sec     ''     ''      sec
 48871.5  -.00036   .50330   .33611  .00015  .00021  .00000  .0 -.08  .00  .00
27 18  0
 48872.5   .00237   .50410   .33421  .00015  .00019  .00000  .0 -.01  .00  .00
27 18  0
 48873.5   .00504   .50512   .33231  .00017  .00020  .00000  .0 -.01  .00  .00
27 18  0
 48874.5   .00754   .50569   .33039  .00016  .00019  .00000  .0  .03  .00  .00
27 18  0
 48875.5   .01027   .50634   .32847  .00016  .00019  .00000  .0  .02  .00  .00
27 18  0
 48876.5   .01170   .50720   .32654  .00016  .00018  .00000  .0  .04  .00  .00
26 18  0
END UTPM TABLE

The following table indicates the "3-dimensional orbit repeatability", as
defined in IGS Mail Message 37, for GPS week 661:

JPL ORBIT REPEATABILITY TABLE                GPS week 661 (1992 Sep 06 - Sep 11)
      92  9  6   92  9  7   92  9  8   92  9  9   92  9 10   92  9 11
prn    rms (m)
  2       1.39       1.10       0.61       0.98       0.82       1.4
  3       1.50       1.04       2.13       5.58       0.91       1.0
 11       0.64       0.51       0.35       0.34       0.73       0.4
 12       1.27       1.52       1.79       1.68       1.52       1.9
 13       1.32       0.91       0.69       1.31       0.40       0.9
 14     427.90     601.40     248.84     469.40       1.91       2.5
 15       0.91       1.07       1.52       0.96       1.07       1.8
 16       3.52       3.00    1473.50    1223.54     636.06     590.0
 17       0.72       0.52       0.83       0.68       1.36       1.0
 18       0.90       1.13       0.40       0.62       0.40       1.2
 19       1.54       1.40       0.96       1.47       1.00       1.8
 20       1.59       1.00       0.98       2.23       1.80       3.7
 21       0.67       1.26       1.02       0.65       1.37       1.3
 23       3.37       1.17       0.81       1.02       0.70       0.3
 24       1.00       0.80       0.47       0.90       0.92       1.6
 25       0.88       0.72       0.94       0.72       1.34       1.0
 26       1.51       0.66       0.57       0.67       0.59       0.9
 28       0.78       0.46       0.33       0.57       0.39       0.8
END ORBIT REPEATABILITY TABLE

As described in IGS Mail Message 37, the following table compares the JPL
precise ephemerides with those from the broadcast ephemeris:

JPL COMPARISON OF BROADCAST NAVIGATION MESSAGE WITH PRECISE EPHEMERIDES
      92  9  6   92  9  7   92  9  8   92  9  9   92  9 10   92  9 11
prn    rms (m)
  2      11.7        9.5        9.0        9.4        8.6        7.9
  3      11.9       12.7       12.9       12.2       16.9       10.5
 11       4.1        3.3        4.2        4.4        5.9        6.7
 12       6.6       15.5        5.1        7.8       13.7        3.6
 13      10.6       11.1       10.7        6.6        6.3        6.7
 14       9.0      780.0      986.7        7.8        9.4       10.3
 15       3.5        5.5        8.0        6.5        4.2        7.6
 16      10.6       10.5       11.0     1158.4      964.4      192.6
 17       5.2        7.7        5.5        4.9        4.5        5.9
 18       6.9        7.5        8.5        8.8        9.3        9.5
 19       4.4        4.1        4.2        3.6        4.1        3.4
 20      11.4        7.6        9.1        8.7        8.6        9.0
 21      10.4        8.7        6.9        5.8        7.5        6.0
 23       7.9        7.0        3.8        2.9        4.0        7.1
 24      13.3       13.7       11.9       13.6        9.6        9.9
 25       6.8        5.3        6.0        7.1        7.5        6.8
 26       7.7        8.7        8.1        9.9       10.1       10.2
 28       3.2        5.5        3.1        3.4        6.0        5.8
END COMPARISON OF BROADCAST NAVIGATION MESSAGE WITH PRECISE EPHEMERIDES

The following table, as explained in IGS Mail Message 91, indicates which
tracking sites were used in this week's analysis:

JPL GROUND STATION INCLUSION TABLE           GPS week 661 (1992 Sep 06 - Sep 11)
      92  9  6   92  9  7   92  9  8   92  9  9   92  9 10   92  9 11

ALBH      X          X          X          X          X          X
ALGO*     X          X          X          X          X          X
FAIR*     X          X          X          X          X          X
GOLD      X          X          X          X          X          X
HART*     X          X          X          X          X          X
HERS      X          X          X          X          X          X
JPLM      X          X          X          X          X          X
KOKB*     X          X          X          X          X          X
KOSG      X          X          X          X          X          X
MADR*     X          X          X          X          X          X
MASP      X          X          X          X          X          X
MATE      X          X          X          X          X          X
MCMU      X          X          X          X          X          X
METS      X          X          X          X          X
NYAL      X          X          X          X          X          X
ONSA      X          X          X          X          X          X
PAMA      X          X          X          X          X          X
PENT      X          X          X          X          X          X
SANT*     X          X          X          X          X          X
STJO      X          X          X          X          X          X
TAIW      X          X          X          X          X          X
TIDB      X          X          X          X          X          X
TROM*     X          X          X          X          X          X
USUD      X          X          X          X          X          X
WETT      X          X          X          X          X          X
YAR1*     X          X          X          X          X          X
YELL      X          X          X          X          X          X
_______________________
*Indicates fiducial site.
END GROUND STATION INCLUSION TABLE

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