From Dennis Wed Sep 23 11:49:23 1992 From: Dennis (Dennis) Date: 23 SEP 1992 11:49:23 Subject: [IGSMAIL-103] Preliminary look at GPS Earth orientation Message-ID: *********************************************************************** IGS Electronic Mail 23-SEP-1992 11:49:23 Message Number 103 *********************************************************************** ============================================================================== THIS FILE CONTAINS 2 MESSAGES ============================================================================== ^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 dmc at maia.usno.navy.mil ============================================================================== ^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 starr at logos.jpl.nasa.gov): ______________________________________________________________________________ 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 ======================================================================