Subject: [IGSMAIL-0654] ESOC IGS Analysis Centre Strategy Summary
From: Tomas J. Martin Mur (ESA/ESOC)
Date: Thu, 30 Jun 1994 8:07:04 PDT

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IGS Electronic Mail      Thu Jun 30  8:07:04 PDT 1994      Message Number 0654
******************************************************************************

Author: Tomas J. Martin Mur (ESA/ESOC)
Subject: ESOC IGS Analysis Centre Strategy Summary

Subject: ESOC IGS Analysis Centre Strategy Summary, June 30, 1994

 ===============================================================================

               INTERNATIONAL GPS SERVICE FOR GEODYNAMICS

                       Analysis Centre Questionnaire

  =============================================================================
  ANALYSIS CENTRE   | ESA/ESOC, European Space Agency / European Space
                    | Operations Centre
                    | Robert-Bosch-Str. 5, D-64293 Darmstadt (Germany)
  -----------------------------------------------------------------------------
  CONTACT PERSON(S) | John M. Dow             e-mail : [email-masked]
                    |                           Tel. : +49-(0)6151-90-2272
                    | Tomas J. Martin Mur     e-mail : [email-masked]
                    |                           Tel. : +49-(0)6151-90-2376
  -----------------------------------------------------------------------------
  SOFTWARE USED     | BAHN, GPSOBS and MULTIARC, developed by ESOC
  -----------------------------------------------------------------------------
  IGS PRODUCTS      | ESA0www0-6.sp3 GPS ephemeris/clock files in 7 daily files
  GENERATED FOR     |                at 15 min intervals in sp3 format,
  GPS WEEK 'www'    |                including accuracy codes
                    | ESA0www7.erp   ERP (pole, LOD) solutions
                    | ESA0www7.sum   Processing summary. Includes sat./station
                    |                daily statistics.
  -----------------------------------------------------------------------------
  PREPARATION DATE  |  June 30, 1994
  =============================================================================

  -----------------------------------------------------------------------------
  |                     MEASUREMENT MODELS                                    |
  |---------------------------------------------------------------------------|
  | Preprocessing    | Independent carrier phase double differences obtained. |
  |                  | Cycle slip detection performed in double difference    |
  |                  | carrier phase observable using almost ionospheric free |
  |                  | integer combinations (4L1-3L2, 5L1-4L2) and computed   |
  |                  | observables based on predicted orbits.                 |
  |                  | Ionospheric free combination formed and centre of mass |
  |                  | and phase wind-up corrections applied.                 |
  |---------------------------------------------------------------------------|
  | Basic Observable | carrier phase for orbit determination, carrier phase   |
  |                  | and pseudo range used for clock estimation             |
  |                  |--------------------------------------------------------|
  |                  | elevation angle cutoff : 20 degrees                    |
  |                  | sampling rates         : 30 sec. (preprocessing)       |
  |                  |                           6 min. (orbit determination) |
  |                  |                           1 min. (clock estimation)    |
  |                  | weighting              : 1 cm for dd carrier phase,    |
  |                  |                          station and satellite         |
  |                  |                          specific for pseudo ranges    |
  |---------------------------------------------------------------------------|
  | Modelled         | double differences of ionospheric free carrier phase   |
  | observable       | used for orbit determination, undifferenced ionospheric|
  |                  | free carrier phase and pseudo range (corrected for     |
  |                  | CA-P biases) used for clock estimation                 |
  |---------------------------------------------------------------------------|
  | RHC phase        | applied in preprocessing                               |
  | rotation corr.   |                                                        |
  |---------------------------------------------------------------------------|
  | Ground antenna   | not applied                                            |
  | phase centre cal.|                                                        |
  |---------------------------------------------------------------------------|
  | Troposphere      | Zenith delay: estimated as linear in 6 hour intervals  |
  |                  |--------------------------------------------------------|
  |                  | Mapping function: a modified Willmann model with the   |
  |                  |                   shape parameter estimated            |
  |---------------------------------------------------------------------------|
  | Ionosphere       | ionospheric free combinations used                     |
  |---------------------------------------------------------------------------|
  | Plate motions    | ITRF 92 station velocities fixed  (see IGSMAIL#421)    |
  |---------------------------------------------------------------------------|
  | Tidal            | Solid earth tidal displacement: Wahr model             |
  | displacements    |--------------------------------------------------------|
  |                  | Pole tide: not applied                                 |
  |                  |--------------------------------------------------------|
  |                  | Ocean loading: not applied                             |
  |---------------------------------------------------------------------------|
  | Atmospheric load.| not applied                                            |
  |---------------------------------------------------------------------------|
  | Satellite center | Block I x,y & z: (0.210, 0, 0.854m)                    |
  | of mass          |--------------------------------------------------------|
  | correction       | Block II/IIA x,y & z :(0.279, 0, 1.026m)               |
  |---------------------------------------------------------------------------|
  | Satellite phase  | not applied                                            |
  | centre calibrat. |                                                        |
  ----------------------------------------------------------------------------

  -----------------------------------------------------------------------------
  |                           ORBIT MODELS                                    |
  |---------------------------------------------------------------------------|
  | Geopotential     | GEM T3 + C21+S21 model up to degree and order 8        |
  |                  |--------------------------------------------------------|
  |                  | GM=398600.4415  km**3/sec**2                           |
  |                  |--------------------------------------------------------|
  |                  | AE = 6378.137 km                                       |
  |---------------------------------------------------------------------------|
  | Third-body       | Sun, Moon and 4 planets regarded as point masses       |
  |                  |--------------------------------------------------------|
  |                  | ephemeris: JPL DE200                                   |
  |                  |--------------------------------------------------------|
  |                  | GMsun = 132712440000.0 km**3/sec**2                    |
  |                  |--------------------------------------------------------|
  |                  | GMmoon = 4902.7991 km**3/sec**2                        |
  |---------------------------------------------------------------------------|
  | Solar radiation  | direct radiation: ROCK4 and ROCK42 approximations      |
  | pressure         |                   denoted as T10 and T20 for           |
  |                  |                   Block I and II satellites, resp.     |
  |                  | area, specularities band reflectivity used: see        |
  |                  | Tables 1,2, (Fliegel and Gallini, 1992, JGR(97)B1,p563)|
  |                  |                                                        |
  |                  | satellite masses used:                                 |
  |                  |  PRN 02    878.15kg        PRN 16-19 883.23kg          |
  |                  |      12    519.82              21    883.90            |
  |                  |      14    887.36              23    972.90            |
  |                  |      15    885.90              20    887.36            |
  |                  |      01, 04-07, 09, 22, 24-29, 31    975.00            |
  |                  |--------------------------------------------------------|
  |                  | one scale factor and one y-bias estimated per arc      |
  |                  |--------------------------------------------------------|
  |                  | Earth shadow model includes: penumbra                  |
  |                  |--------------------------------------------------------|
  |                  | reflection radiation: not included                     |
  |                  |--------------------------------------------------------|
  |                  | "biased yaw" GPS satellite attitude model: not applied |
  |---------------------------------------------------------------------------|
  | Tidal forces     | solid earth tides: Wahr model, k2 = 0.300              |
  |                  |--------------------------------------------------------|
  |                  | Ocean tides: Schwiderski model                         |
  |---------------------------------------------------------------------------|
  | Relativity       | applied only to clock estimates                        |
  |---------------------------------------------------------------------------|
  | Numerical        | Adams-Bashforth/Adams-Moulton predictor-corrector of   |
  | Integration      | order 8.                                               |
  |                  |--------------------------------------------------------|
  |                  | integration step: 6 minutes                            |
  |                  |--------------------------------------------------------|
  |                  | starter procedure: Runge-Kutta/Shanks of order 8       |
  |                  |--------------------------------------------------------|
  |                  | arc length: 48 hours ( 12 + 24 + 12 )                  |
  -----------------------------------------------------------------------------

  -----------------------------------------------------------------------------
  |                    ESTIMATED PARAMETERS (APRIORI VALUES & SIGMAS)         |
  |---------------------------------------------------------------------------|
  | Adjustment       | Weighted least-squares used for orbit determination    |
  |                  | Sequential Kalman filter used for clock estimation     |
  |---------------------------------------------------------------------------|
  | Rejection Criter.| 3 times residual rms used for orbit determination      !
  |---------------------------------------------------------------------------|
  | Station          | 13 stations fixed to the ITRF92 positions as given in  |
  | coordinates      | IGSMAIL#430, the remaining stations estimated (50m     |
  |                  | apriori sigmas). ITRF92 velocities used.               |
  |                  | For combined station coordinate solutions all stations |
  |                  | are unconstrained                                      |
  |---------------------------------------------------------------------------|
  | Orbital          | Initial position and velocity, solar radiaton pressure |
  | parameters       | scale factor and y-bias estimated as constant through  |
  |                  | the orbital arc, with the following apriori sigmas     |
  |                  | w.r.t. the values predicted from the previous day:     |
  |                  | x, y, z:             - 100m                            |
  |                  | Vx, Vy, Vz:          - 1m/s                            |
  |                  | s.r.p. scale factor  - 0.1                             |
  |                  | y-bias               - 1d-9 m/s**2                     |
  |---------------------------------------------------------------------------|
  | Troposphere      | Zenith delay and shape factor estimated as linear      |
  |                  | within six hour intervals, with continuity between     |
  |                  | intervals. Apriori values taken from previous day with |
  |                  | sigmas of:                                             |
  |                  | zenith delay:        - 0.2m                            |
  |                  | shape factor:        - 10%                             |
  |---------------------------------------------------------------------------|
  | Ionospheric      | no parameters estimated                                |
  | correction       |                                                        |
  |---------------------------------------------------------------------------|
  | Ambiguity        | estimated as real values, one for every continuous     |
  |                  | double difference pass between cycle slips. Apriori    |
  |                  | values obtained in the preprocessing, sigma of 3.D8 m  |
  |---------------------------------------------------------------------------|
  | ERP              | x & y pole, and LODR estimated. Current IERS Bulletin  |
  |                  | B values used as apriori. Estimated constant during    |
  |                  | a 24h period (UTC day), UT1-UTC at 12:00 of the central|
  |                  | day fixed to the IERS value.                           |
  |                  | Apriori sigmas used:                                   |
  |                  | x,y pole       - 100 mas                               |
  |                  | LOD            - 6.48 ms/day.                          |
  |---------------------------------------------------------------------------|
  | Satellite and    | For orbit determination double differences are used    |
  | receiver clock   | and only receiver clock biases and drifts are estimated|
  | biases           | as constant parameters between clock resets. Initial   |
  |                  | values obtained in the preprocessing and constrained   |
  |                  | with 1 microsec, 1 microsec/day sigmas.                |
  |                  | After the orbit determination pseudo-range biases are  |
  |                  | estimated using the residuals of double-differenced    |
  |                  | pseudo-ranges.                                         |
  |                  | In post-processing satellite and receiver clock biases |
  |                  | and drifts are modelled as exponentially correlated    |
  |                  | random variables (ecrv) and obtained every 1 minute.   !
  |                  | For estimation of the clock biases at the first epoch  |
  |                  | the following is used:                                 |
  |                  |  Corrected pseudo-range observations with weights      |
  |                  |   about 3 ns and rejection threshold at 9 ns           |
  |                  |  Navigation message clock biases, with a weight of     |
  |                  |   100 ns                                               |
  |                  | For clock drift estimation the following is used:      |
  |                  |  Time differenced carrier phase observations, with a   |
  |                  |   weight of 0.1 mm/sec (0.3D-12 s/s).                  |
  |                  |  Navigation message clock drift, with a weight of      |
  |                  |   1.d-9 s/s.                                           |
  |                  |  Variability of clock drifts (except for clock resets):|
  |                  |   Satellite clocks:           1 ns/s in 60 sec         |
  |                  |   H-maser clocks:             0.0002 ns/s in 60 sec    |
  |                  |   Other receiver clocks:      1 ns/s in 60 sec         |
  |                  | For clock bias estimation the following is used:       |
  |                  |  Integrated drift observations, with a weight of 0.2 ns|
  |                  |  Corrected pseudo-range observations, with weights     |
  |                  |   about 3 ns                                           |
  |                  |  Navigation message clock bias with a weight of 100 ns |
  |                  |  Variability of clock biases (except for clock resets):|
  |                  |   Satellite clocks:           100 ns in 60 sec         |
  |                  |   H-maser clocks:             0.04 ns in 60 sec        |
  |                  |   Other receiver clocks:      200 ns in 60 sec         |
  |                  | WARNING: no L1-L2 satellite calibration applied, so    |
  |                  | the satellite clocks include part of the L1-L2         |
  |                  | calibration delays                                     |
  |---------------------------------------------------------------------------|
  | Other            | Manoeuvres are detected in the preprocessing using     |
  | parameters       | time differenced carrier phase residuals corrected for |
  |                  | clock biases and estimated in the main orbit           |
  |                  | determination as an impulsive delta-V.                 |
  |                  |                                                        |
  |                  | CA-P Pseudorange biases daily estimated using double   |
  |                  | differenced pseudo range residuals.                    |
  -----------------------------------------------------------------------------

  -----------------------------------------------------------------------------
  |                       REFERENCE FRAMES                                    |
  |---------------------------------------------------------------------------|
  | Inertial         | Geocentric; mean equator and equinox of 2000 Jan 1     |
  |                  | at 12:00 (J2000.0)                                     |
  |---------------------------------------------------------------------------|
  | Terrestrial      | ITRF92 reference frame realized through the set of 13  |
  |                  | station coordinates and velocities as given in IGSMAIL#|
  |                  | 430 as well as the antenna offsets for the above       |
  |                  | stations given in /igscb/station/tie/localtie.tab      |
  |                  | available from IGS CB (sideshow.jpl.nasa.gov)          |
  |---------------------------------------------------------------------------|
  | Interconnection  | Precession: IAU 1976 Precession Theory                 |
  |                  |--------------------------------------------------------|
  |                  | Nutation: IAU 1980 Nutation Theory                     |
  |                  |--------------------------------------------------------|
  |                  | Celestial pole offsets from IERS Bulletin B            |
  |                  |--------------------------------------------------------|
  |                  | Relationship between UT1 and GMST: Aoki et al. (1982)  |
  |                  |--------------------------------------------------------|
  |                  | ERP interpolated from IERS Bulletin B (updated every   |
  |                  | two weeks. No celestial pole corrections)              |
  |                  |--------------------------------------------------------|
  |                  | Tidal variations in UT1: Yoder model                   |
  -----------------------------------------------------------------------------

  References:

  D.C. Brown, Advanced techniques for the reduction of geodetic SECOR
  observations, NASA Ref. STAR N67-15035, July 1966.

  J.M. Dow, T.J. Martin Mur, J. Feltens, C. Garcia Martinez, The ESOC GPS
  Facility: Report on the IGS 1992 Campaign and Outlook, Proceedings of
  the 1993 IGS Workshop, held at the Univ. of Berne, Switzerland, March
  1993, pp.133-144.

  J.M. Dow, T.J. Martin Mur, C. Garcia Martinez, J. Feltens, M.A. Bayona
  Perez, ESA/ESOC IGS Analysis Centre Status March 1994, presented at the
  IERS/IGS workshop held at IGN, March 1994.

  J.M. Dow, T.J. Martin Mur, M.M. Romay Merino, ESA's Precise Orbit
  Determination Facility, ESA Bulletin no. 78, May 1994, pp.40-50.

  H. Fliegel, T. Gallini and E. Swift, Global Positioning System radiation
  force model for geodetic applications, J.Geophys.Res. 97(B1), pp. 559-568,
  January 1992.

  T.J. Martin Mur, J.M. Dow, J. Feltens, C. Garcia Martinez, ESOC report
  to the 1993 IGS Analysis Centre Workshop, Ottawa, Canada, October 1993.

  T.J. Martin Mur, J.M. Dow, J. Feltens, C. Garcia Martinez, Annual report
  from the ESOC/IGS Analysis Centre to the IERS for 1993, presented in
  the 1994 IGS/IERS workshop held at the Observatoire de Paris, France,
  March 1994.

  D.D. McCarthy (ed.), IERS Standards (1992), IERS Technical Note 13,
  Observatoire de Paris, July 1992.

  J.T. Wu, S.C. Wu, G.A. Hajj, W.I. Bertiger, S.M. Lichten, Effects of
  antenna orientation on GPS carrier phase, Manuscripta Geodaetica (1993)
  18, pp. 91-98.

 ===============================================================================
 Tomas J. Martin Mur
 Orbit and Attitude Division            Tel.  : +49 6151 902376
 ESA, European Space Operations Centre  Fax   : +49 6151 902271
 Robert-Bosch-Str.5,                    Telex : 419 453 EU D
 D-64293 Darmstadt (Germany)            e-mail: [email-masked]

[Mailed From: Tomas Martin Mur <[email-masked]>]