============================================================================= | IGS Re-Analysis Strategy Summary | ============================================================================= | Analysis Center | GeoForschungsZentrum (GFZ) Potsdam | | | Telegrafenberg A17 | | | D-14473 Potsdam | | | Germany | | | Phone: +49 331 288 11 00 | | | Fax: +49 331 288 11 11 | | | | | | Institut fuer Planetare Geodaesie | | | Technische Universitaet Dresden (TUD) | | | Helmholtzstraße 10 | | | D-01062 Dresden | | | Germany | | | Phone: +49 351 463 346 52 | | | Fax: +49 351 463 370 63 | |---------------------------------------------------------------------------| | Contact people | Peter Steigenberger (GFZ, now at TU Munich) | | | E-mail: steigenberger@bv.tum.de | | | Phone: +49 89 289 231 93 | | | | | | Mathias Fritsche (TUD) | | | E-mail: fritsche@ipg.geo.tu-dresden.de | | | Phone: +49 351 463 338 40 | | | | | | Axel Ruelke (TUD) | | | E-mail: ruelke@ipg.geo.tu-dresden.de | | | Phone: +49 351 463 338 40 | |---------------------------------------------------------------------------| | Software used | Bernese GPS Software Version 5.1, developed at AIUB | | | modified at GFZ, TUD, TUM | |---------------------------------------------------------------------------| | IGS products | ACNwwwwn.sp3 daily orbit files | | generated for | ACNwwww?.erp daily/weekly ERP file | | GPS Week wwww | ACNwwwwn.clk daily station and SV clock files | | day of Week n | ACNwwww?.sum daily/weekly summary file | | (n=0,1,...,6) | ACNwwww?.snx daily/weekly SINEX file | | | ACNwwwwn.tro daily tropo files | | | [ACN = Analysis Center code] | | | [wwww = GPS week number] | | | [n = GPS day of week number] | |---------------------------------------------------------------------------| | Preparation date | Draft version of 2006-04-26 | |---------------------------------------------------------------------------| | Modification dates| 2006-11-02, PS: clarified sampling rate | | | 2007-10-10, PS: modified contact info of PS | | | added reference for TUM PCVs | | | 2008-05-15, PS: added some missing information: | | | met data input; k2 | | | gravity: solid Earth pole tide | | | | | | YYYY-MM-DD: ... [summary of changes] | |---------------------------------------------------------------------------| | Effective date | 2005-05-04 | | for data analysis | | ============================================================================= ============================================================================= | MEASUREMENT MODELS | |---------------------------------------------------------------------------| | Preprocessing | Phase preprocessing in a baseline by baseline mode | | | using triple-differences. In most cases, cycle slips | | | are fixed looking simultaneously at different linear | | | combinations of L1 and L2. If a cycle slip cannot be | | | fixed reliably, bad data points are removed or new | | | ambiguities are set up. In addition, a data screening | | | step on the basis of weighted postfit residuals is | | | performed. Outliers are removed. | |---------------------------------------------------------------------------| | Basic observable | Carrier phase; code only used for receiver clock | | | synchronization, MW ambiguity resolution, ionosphere | | | estimation, P1C1-DCB estimation. | | |--------------------------------------------------------| | | elevation angle cutoff: 3 degrees | | | sampling rate: 30 sec for preprocessing | | | 3 min in final parameter | | | estimation step | | | weighting: carrier phase= 3 mm for double-differenced | | | ionosphere-free phase | | | observations at zenith | | | deweighting: elevation-dependent weighting function | | | 1/cos(z)**2 | | | smoothing: | | code biases: P1P2 and P1C1 DCBs estimated | |---------------------------------------------------------------------------| | Modeled | Double differences, ionosphere-free linear combination;| | observable | zero differences for ionosphere estimation and | | | P1C1-DCB estimation. | |---------------------------------------------------------------------------| |*Satellite center | SV-specific z-offsets & block-specific x- & y-offsets | | of mass | (from manufacturer): TUM05, TUM contribution to igs05, | | offsets | Schmid et al. (2007). | |---------------------------------------------------------------------------| |*Satellite phase | Block-specific nadir-dependent absolute PCVs applied: | | center | TUM05, TUM contribution to igs05, Schmid et al. (2007) | | offsets | no azimuth-dependent corrections applied. | | corrections | | |---------------------------------------------------------------------------| |*Satellite clock | 2nd order relativistic correction for non-zero | | corrections | orbit ellipticity (-2*R*V/c) applied. | |---------------------------------------------------------------------------| | GPS attitude | Not applied | | model | | |---------------------------------------------------------------------------| |*RHC phase | Phase wind-up applied according to Wu et al. (1993). | | rotation corr. | | |---------------------------------------------------------------------------| |*Ground antenna | Absolute elevation- & azimuth-dependent (when | | phase center | available) PCVs & L1/L2 offsets from ARP applied: | | offsets and | TUM05. | | corrections | | |---------------------------------------------------------------------------| |*Antenna radome | Not applied | | calibration | | |---------------------------------------------------------------------------| |*Marker -> antenna| dN,dE,dU eccentricities from site logs applied to | | ARP eccentricity | compute station coordinates. | |---------------------------------------------------------------------------| | Troposphere | met data input: Standard atmosphere, Berg (1948) | | a priori model |--------------------------------------------------------| | | zenith delay: Hydrostatic component according to | | | Saastamoinen (1973). | | |--------------------------------------------------------| | | mapping function: Dry Isobaric Mapping fuction (IMF) | | | with ECMWF data, Niell (2000). | |---------------------------------------------------------------------------| |*Ionosphere | 1st order effect: Eliminated by forming the | | | ionosphere-free linear combination | | | of L1 and L2. | | |--------------------------------------------------------| | | 2nd order effect: Applied accorindg to | | Fritsche et al (2005). | | |--------------------------------------------------------| | | other effects: 3rd order effect applied according to | | | Fritsche et al (2005). | |---------------------------------------------------------------------------| |*Tidal | solid Earth tide: IERS 2003 | | displacements |--------------------------------------------------------| | | permanent tide: Zero-frequency contribution left in | | | tide model, not in site coordinates. | | |--------------------------------------------------------| | | solid Earth pole tide: IERS 1996 with constant pole | | | offsets: xp=0.033, yp=0.331 as. | | |--------------------------------------------------------| | | oceanic pole tide: Not applied | | |--------------------------------------------------------| | | ocean tide loading: IERS 2003 | | |--------------------------------------------------------| | | ocean tide coeffs: GOT00.2 | | |--------------------------------------------------------| | | ocean tide geocenter: Not applied | | |--------------------------------------------------------| | | atmosphere tides: Not applied | |---------------------------------------------------------------------------| | Non-tidal | atmospheric pressure: Not applied | | loadings |--------------------------------------------------------| | | ocean bottom pressure: Not applied | | |--------------------------------------------------------| | | surface hydrology: Not applied | | |--------------------------------------------------------| | | other effects: Not applied | |---------------------------------------------------------------------------| |*Earth orientation| ocean tidal: IERS 2003 | | variations |--------------------------------------------------------| | | atmosphere tidal: Not applied | | |--------------------------------------------------------| | | high-frequency nutation: Not applied | ============================================================================= ============================================================================= | REFERENCE FRAMES | |---------------------------------------------------------------------------| | Time argument | GPS time as given by observation epochs, which is | | | offset by only a fixed constant (approx.) from TT/TDT. | |---------------------------------------------------------------------------| | Inertial | Geocentric; mean equator and equinox of 2000 Jan 1.5 | | | (J2000.0). | |---------------------------------------------------------------------------| | Terrestrial | ITRF2000 reference frame realized through the set of | | | up to 99 stations coordinates and velocities given in | | | the IGS internal realization IGS03P33_RS106.snx. | |---------------------------------------------------------------------------| | Tracking | Nominally 202 stations, up to 160 per day | | network | all IGb00 stations + co-locations with DORIS, SLR, | | | VLBI, tide gauges + others. | |---------------------------------------------------------------------------| | Interconnection |*precession: IAU 1976 | | |--------------------------------------------------------| | |*nutation: IAU2000A | | |--------------------------------------------------------| | | a priori EOPs: Bulletin A | ============================================================================= ============================================================================= | ORBIT MODELS | |---------------------------------------------------------------------------| | Geopotential | JGM3 to degree and order 12 | | (static) | time-variable coefficients: C20 | | |--------------------------------------------------------| | | GM = 398600.4415 km**3/sec**2 | | |--------------------------------------------------------| | | AE = 6378.137 km | |---------------------------------------------------------------------------| |*Tidal variations | solid earth tides: k2=0.3 | | in geopotential |--------------------------------------------------------| | | ocean tides: CSR 3.0 | | |--------------------------------------------------------| | | solid Earth pole tide: IERS 1996 with constant pole | | | offsets: xp=0.033, yp=0.331 as. | | |--------------------------------------------------------| | | oceanic pole tide: Not applied | |---------------------------------------------------------------------------| | Third-body | Sun, Moon, Venus, Mars, Jupiter | | forces | (regarded as point masses) | | |--------------------------------------------------------| | | ephemeris: JPL DE405 | | |--------------------------------------------------------| | | GM Sun 132712500000.0000 km**3/sec**2 | | | Moon-Earth mass ratio | | | Sun-Mercury mass ratio | | | Sun-Venus mass ratio | | | Sun-Mars mass ratio | | | Sun-Jupiter mass ratio | | | Sun-Saturn mass ratio | |---------------------------------------------------------------------------| | Solar radiation | a priori: ROCK4 and ROCK42 approximations (T10 and | | pressure model | T20) for Block I and II SVs. | | |--------------------------------------------------------| | | Earth shadow model: Cylinder model | | |--------------------------------------------------------| | | Earth albedo: Not applied | | |--------------------------------------------------------| | | Moon shadow: Umbra & penumbra model | | |--------------------------------------------------------| | | satellite attitude: Not applied | |---------------------------------------------------------------------------| |*Relativitic | dynamical correction: IERS 2003, Ch. 10, eqn 1 | | effects | (except Lense-Thirring & geodesic precession | | | terms neglected). | | |--------------------------------------------------------| | | gravitational time delay: IERS 2003, Ch. 11, eqn 17 | |---------------------------------------------------------------------------| | Numerical | method: Representation of the the orbit by a | | integration | polynomial of degree 10 for 1 hour. | | |--------------------------------------------------------| | | integration step: 1 hour | | |--------------------------------------------------------| | | starter procedure: No special starter procedure needed | | |--------------------------------------------------------| | | arc length: 72 hours | ============================================================================= ============================================================================= | ESTIMATED PARAMETERS (APRIORI VALUES AND CONSTRAINTS) | |---------------------------------------------------------------------------| | Adjustment | Weighted least-squares algorithms | | method | | |---------------------------------------------------------------------------| | Station | All station coordinates are adjusted, 3 no-net | | coordinates | rotation conditions wrt IGb00 are imposed; geocenter | | | coordinates constrained nominally to zero values. | |---------------------------------------------------------------------------| | Satellite clocks | Not estimated but eliminated by forming double | | | differences. | |---------------------------------------------------------------------------| | Receiver clocks | Receiver clock corrections are estimated during the | | | preprocessing using pseudorange measurements. | |---------------------------------------------------------------------------| | Orbits | 6 Keplerian elements plus 5 solar radiation parameters | | parameters | at start of arc; no a priori sigmas used. | | | Estimated RPR parameters, Beutler (1994) | | | - constants in D-, Y- and X-direction | | | - periodic terms in X-direction | | | Pseudo-stochastic orbit pulses (small velocity | | | changes, constrained to 1.E-6 m/sec in radial | | | 1.E-5 m/sec in along-track and 1.E-9 in cross-track | | | direction) are estimated every 12 hours for all | | | satellites. | |---------------------------------------------------------------------------| | Satellite | Not estimated | | attitude | | |---------------------------------------------------------------------------| | Troposphere | zenith delay: Contineous piece-wise linear troposphere | | | zenith delay parameters are estimated | | | for each station with intervals of 2 | | | hours. Weak a priori constraints of | | | 2.5 m are applied. | | |--------------------------------------------------------| | | mapping fuction: Wet Niell Mapping Function | | | Niell (1996) | | |--------------------------------------------------------| | | zenith delay epochs: 00:00, 02:00, ..., 24:00 | | |--------------------------------------------------------| | | gradients: One pair of N-S and E-W gradient parameter | | | per day and station. | |---------------------------------------------------------------------------| | Ionospheric | Not estimated in ionosphere-free analyses. | | corrections | | |---------------------------------------------------------------------------| | Ambiguities | Ambiguities are resolved in a baseline-by-baseline | | | mode. The strategy depends on the baseline length: | | | < 6000 km Melbourne-Wuebbena | | | < 2000 km QIF | | | < 200 km widelane/narrowlane | | | < 20 km L1/L2 | |---------------------------------------------------------------------------| |*Earth Orientation| Contineous piece-wise linear X- and Y-pole coordinates | | Parameters (EOP) | and UT1-UTC are estimated with intervals of 24 hours. | | | UT1-UTC is fixed to the a priori value at the | | | beginning of the first day. No further a priori sigmas | | | are used. | | | | | | Drifts in nutation (Dpsi, Deps) are solved for in a | | | special 3-day solution. The corresponding nutation | | | parameters generally set up are usually heavily | | | constrained to the IAU 2000 model. | | | | | | High-rate (2-hour) X-, Y- and UT1-UTC estimates are | | | also generated in a special 3-day solution. | |---------------------------------------------------------------------------| | Other parameters | GPS satellite antenna phase center variations: | | | | | | Corresponding parameters are set up for each satellite | | | and usually heavily constrained to the a priori values | ============================================================================= ============================================================================= | REFERENCES | |---------------------------------------------------------------------------| | Berg, H., Allgemeine Meteorologie, Duemmlers Verlag, Bonn, 1948 | | | | Beutler, G., E. Brockmann, W. Gurtner, U. Hugentobler, L. Mervart, | | M. Rothacher, and A. Verdun, Extended orbit modeling techniques at the | | CODE processing center of the international GPS service for Geodynamics | | (IGS): theory and initial results, Manuscripta Geodaetica, 19, 367-386, | | 1994. | | | | Fritsche, M., R. Dietrich, C. Knoefel, A. Ruelke, S. Vey, M. Rothacher, | | and P. Steigenberger, Impact of higher-order ionospheric terms on GPS | | estimates. Geophysical Research Letters, 32, 2005. | | | | Niell, A., Global mapping functions for the atmosphere delay at radio | | wavelengths, J. Geophys. Res., 101(B2), 3227-3246, 1996. | | | | Niell, A., Improved atmospheric mapping functions for VLBI and GPS, | | Earth Planets Space, 52, 699-702, 2000. | | | | Saastamoinen, J., Contributions to the Theory of Atmospheric Refraction, | | Bulletin Geodesique, 107, 13-34, 1973. | | | | Schmid, R., P. Steigenberger, G. Gendt, M. Ge, M. Rothacher, Generation | | of a consistent absolute phase center correction model for GPS receiver | | and satellite antennas, Journal of Geodesy, 2007. | | | | Wu, J.T., S.C. Wu, G.A. Hajj, W.I. Bertiger, and S.M. Lichten, Effects of | | antenna orientation on GPS carrier phase, Manuscripta Geodaetica,18, | | 91-98, 1993. | ============================================================================= |* = strong consistency with IERS/IGS conventions is especially important | | for these items | =============================================================================