Subject: [IGSMAIL-2259] Processing changes at ESOC
From: ESOC IGS team
Date: Tue, 4 May 1999 4:45:55 PDT

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IGS Electronic Mail      Tue May  4  4:45:55 PDT 1999      Message Number 2259
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Author: ESOC IGS team
Subject: Processing changes at ESOC

Subject: Processing changes at ESOC

Dear Colleagues,

Starting with our final products for GPS week 1006 we have changed 
the basic observable in our processing. Instead of using double 
differences we use undifferenced carrier and pseudorange as main 
observables. In this way orbits and clocks are solved simultaneously
and they are consistent one each other. Our products also benefit 
from the better observability of undifferenced processing with respect 
to double differences.

We will also shortly use the same strategy for the computation
of the rapid products.

The new Analysis Centre Form is included below.

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

                  INTERNATIONAL GPS SERVICE FOR GEODYNAMICS

                    ESA/ESOC Processing Strategy Summary

=============================================================================
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 BATUSI, developed by ESOC
-----------------------------------------------------------------------------
FINAL IGS PRODUCTS| ESAwwwwd.sp3   GPS ephemeris/clock files in 7 daily files
GENERATED FOR     |                at 15 min intervals in sp3 format,
GPS WEEK 'wwww'   |                including accuracy codes
DAY OF WEEK 'd'   | ESAwwww7.erp   ERP (pole, LOD) solutions
                  | ESAwwww7.sum   Processing summary. Includes sat./station
                  |                daily statistics.
                  | ESAwwww7.snx   SINEX file
                  | ESAwwwwd.tro   Tropospheric delay files

RAPID IGS PRODUCTS| ESAwwwwd.sp3   Orbit files
                  | ESAwwwwd.erp   ERP files

PREDICTED ORBITS  | ESPwwwwd.sp3

-----------------------------------------------------------------------------
PREPARATION DATE  |  May 4, 1999
=============================================================================

-----------------------------------------------------------------------------
|                     MEASUREMENT MODELS                                    |
|---------------------------------------------------------------------------|
| Preprocessing    | Pass selection based on lenght and noise. Cycle slip   |
|                  | detection performed using the geometry free and wide   |
|                  | lane combinations. Centre of mass and phase wind-up    |
|                  | corrections applied.                                   |
|---------------------------------------------------------------------------|
| Basic Observable | carrier phase and pseudo range                         |
|                  |--------------------------------------------------------|
|                  | elevation angle cutoff : 10 degrees                    |
|                  | sampling rates         : 30 sec. (preprocessing)       |
|                  |                           5 min. (orbit determination) |
|                  |                           5 min. (clock estimation)    |
|                  | weighting              : 1 cm for carrier phase,       |
|                  |                        : 3  m for pseudorange          |
|---------------------------------------------------------------------------|
| Modelled         | Independent ionospheric-free undifferenced carrier     |
| observable       | phase and pseudorange observations.                    |
|---------------------------------------------------------------------------|
| RHC phase        | applied in preprocessing                               |
| rotation corr.   |                                                        |
|---------------------------------------------------------------------------|
| Ground antenna   | Elevation dependent following the IGS_01 model         |
| phase centre cal.|                                                        |
|---------------------------------------------------------------------------|
| Troposphere      | Saastamoinen model with estimated Zenith delay         |
|                  | every 2 hours as a step function                       |
|---------------------------------------------------------------------------|
| Ionosphere       | ionospheric free combinations used                     |
|---------------------------------------------------------------------------|
| Plate motions    | ITRF 96 station velocities fixed when available, NNR-  |
|                  | Nuvel otherwise                                        |
|---------------------------------------------------------------------------|
| Tidal            | Solid earth tidal displacement: Wahr model             |
| displacements    |--------------------------------------------------------|
|                  | Pole tide: not applied                                 |
|                  |--------------------------------------------------------|
|                  | Ocean loading: OSO coefficients                        |
|---------------------------------------------------------------------------|
| 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, 1.023m)               |
|                  |--------------------------------------------------------|
|                  | Block IIR    x,y & z :(0.000, 0, 0.000m)               |
|---------------------------------------------------------------------------|
| 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                           |
|---------------------------------------------------------------------------|
| Third-body       | Sun, Moon and 4 planets (Venus,Mars,Jupiter,Saturn)    |
|                  | 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, ROCK42 and T30 approximations |
| pressure         |                   denoted as T10, T20 and T30 for      |
|                  |                   Block I, II and IIR 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 final orbits: 48 hours ( 12 + 24 + 12 )     |
|                  | arc length rapid orbits: 36 hours ( 12 + 24 )          |
-----------------------------------------------------------------------------

-----------------------------------------------------------------------------
|                    ESTIMATED PARAMETERS (APRIORI VALUES & SIGMAS)         |
|---------------------------------------------------------------------------|
| Adjustment       | Weighted least-squares with estimation of time         |
|                  | dependent parameters on every iteration                |
|---------------------------------------------------------------------------|
| Station          | ITRF96 core stations constrained with 3 mm, the        |
|                  | remaining stations estimated with 50m apriori sigmas.  |
| coordinates      | ITRF96 velocities used if availalable, otherwise Nuvel-|
|                  | NNR.                                                   |
|---------------------------------------------------------------------------|
| 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               |
|                  | One cycle per revolution empirical accelerations. Sine |
|                  | and cosine of the radial component are estimated with  |
|                  | apriori sigma              - 1d-12                     |
|---------------------------------------------------------------------------|
| Troposphere      | Zenith delays estimated as two hours step functions.   |
|                  | Apriori values taken from previous day with sigmas     |
|                  | of 0.2m                                                |
|---------------------------------------------------------------------------|
| Ionospheric      | no parameters estimated                                |
| correction       |                                                        |
|---------------------------------------------------------------------------|
| Ambiguity        | estimated as real values, one for every continuous     |
|                  | pass between cycle slips. Apriori values obtained      |
|                  | in the preprocessing, sigma of 3.D8 m                  |
|---------------------------------------------------------------------------|
| ERP              | x & y pole, and LOD  estimated. Current IERS Bulletin  |
|                  | B values used as apriori. Estimated linear during      |
|                  | a 24h period (UTC day). Equivalent to mean value and   |
|                  | rates.                                                 |
|                  | Apriori sigmas used:                                   |
|                  | x,y pole       - 100 mas                               |
|                  | LOD            - 6.48 ms/day.                          |
|---------------------------------------------------------------------------|
| Satellite clock  | Solved for every epoch. No L1-L2 satellite calibration |
|---------------------------------------------------------------------------|
| Receiver clock   | Solved for every epoch. No P1-P2 receiver calibration  |
| bias             | A combination of the most stable station clocks used as|
|                  | time reference. The selection is performed every day.  |
|---------------------------------------------------------------------------|
| 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.                 |
-----------------------------------------------------------------------------

-----------------------------------------------------------------------------
|                       REFERENCE FRAMES                                    |
|---------------------------------------------------------------------------|
| Inertial         | Geocentric; mean equator and equinox of 2000 Jan 1     |
|                  | at 12:00 (J2000.0)                                     |
|---------------------------------------------------------------------------|
| Terrestrial      | ITRF96 reference frame realized through the set of core|
|                  | station coordinates and velocities as given in         |
|                  | ITRF96.SNX                                             |
|---------------------------------------------------------------------------|
| Interconnection  | Precession: IAU 1976 Precession Theory                 |
|                  |--------------------------------------------------------|
|                  | Nutation: IAU 1980 Nutation Theory                     |
|                  |--------------------------------------------------------|
|                  | Celestial pole offsets from IERS Bulletin A            |
|                  |--------------------------------------------------------|
|                  | Relationship between UT1 and GMST: Aoki et al. (1982)  |
|                  |--------------------------------------------------------|
|                  | ERP interpolated from IERS Bulletin A (updated twice a |
|                  | week)                                                  |
|                  |--------------------------------------------------------|
|                  | Tidal variations in UT1 and xp: Ray model              |
-----------------------------------------------------------------------------

References:

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.

[Mailed From: "C. Garcia Martinez x2088 A141 gmv/fcsd/oad" <[email-masked]>]