============================================================================= | | | | | INTERNATIONAL GNSS SERVICE | | | | USNO Ultra-Rapid Analysis Strategy Summary | | | | | ============================================================================= | Analysis Center | U.S. Naval Observatory | | | Earth Orientation Dept. | | | 3450 Massachusetts Avenue, NW | | | Washington, DC 20392-5420 | | | USA | | | Phone: see below | | | Fax: 202-762-1563 | |---------------------------------------------------------------------------| | Contact People | Christine Hackman: hackman.christine@usno.navy.mil | | | Sharyl Byram: sharyl.byram@usno.navy.mil | | | Victor Slabinski: slabinski.victor@usno.navy.mil | | | Jeffrey Tracey: jeffrey.tracey@usno.navy.mil | | | | | | Telephone numbers: | | | | | | Hackman: 202-762-1428 | | | Byram: 202-550-6407 | | | Slabinski: 202-762-0365 | | | Tracey: 202-762-0403 | ----------------------------------------------------------------------------- | Software Used | Bernese GPS Software Version 5 | ----------------------------------------------------------------------------- | IGS Ultra-rapid | Contributions to IGS Ultra-Rapid combination | | Products | beginning 26 February 2007: | | Generated for | | | GPS Week 'wwww' | usuwwwwn_hh.sp3 GPS ephemeris files for 24-hr | | Day of Week 'n' | observed and 24-hr predicted spans | | (n = 0, 1, ...6) | where the middle epoch is wwwwn_hh | | GPS Hour 'hh' | GPST, tabulated at 15-min intervals | | (hh=00,06,12,18) | in sp3 format. Includes estimated | | | accuracy codes. | | | | | | usuwwwwn_hh.erp EOP (pole, pole rates and LOD | | | estimates; a priori UT1-UTC) for | | | 24-hr observed and 24-hr predicted | | | spans. | |---------------------------------------------------------------------------| | Preparation Date | 23 Sep. 2008 | |---------------------------------------------------------------------------| | Effective Date | 12 Jun. 2008 | | 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 | GPS carrier phase and code | | |--------------------------------------------------------| | | Elevation angle cutoff : 3 degrees | | | Sampling rate : 3 minutes | | | Weighting : a priori uncertainty of 1 mm | | | for L1 carrier-phase | | | measurements; | | | elevation-dependent weighting| | | function [1/cos(z)**2] | | | applied | |---------------------------------------------------------------------------| | Modeled | Double differences, ionosphere-free linear combination | | observable | | |---------------------------------------------------------------------------| | RHC phase | Phase polarization effects applied (Wu et al., 1993) | | rotation corr. | | |---------------------------------------------------------------------------| | Ground antenna | IGS05 PCV model applied starting 12 Jun. 2008; IGS01 | | phase center | model applied prior to that. | | calibrations | | |---------------------------------------------------------------------------| | Troposphere | A priori model : Standard values p, T, RH; | | | Saastamoinen zenith delay; dry | | | Niell mapping function; apriori | | | azimuthal gradients set to zero. | | |--------------------------------------------------------| | | Met data input : No met measurements used. | | |--------------------------------------------------------| | | Estimation : Zenith delay corrections are | | | estimated in piecewise-constant | | | 2-hour intervals. | | | N-S and E-W horizontal delay | | | parameters are solved for every | | | 24 hours. | | |--------------------------------------------------------| | | Constraints : Both zenith and gradient parameters | | | are treated as completely | | | unconstrained. | | |--------------------------------------------------------| | | Mapping function: wet Niell | |---------------------------------------------------------------------------| | Ionosphere | Not modeled (first-order effect eliminated by forming | | | the ionosphere-free linear combination of L1 and L2). | |---------------------------------------------------------------------------| | Plate motions | IGS05 station velocities | |---------------------------------------------------------------------------| | Tidal | Solid earth tidal displacement: complete model from | | displacements | IERS Conventions 2003 | | | | | | Permanent tidal term : applied in tide model, | | | NOT included in site | | | coordinates | | |--------------------------------------------------------| | | Pole tide : applied (IERS, 2003) | | |--------------------------------------------------------| | | Ocean tidal loading: GOT002.BLQ; long-period tides | | | from FES99. | |---------------------------------------------------------------------------| | Atmospheric load.| Not applied | |---------------------------------------------------------------------------| | Earth orientation| Tidal UT1 (> 5 days): modeled | | models (EOP) | Subdaily ERPs : IERS2000 model | | | | | | Nutation + | | | Precession : IAU2000 model | |---------------------------------------------------------------------------| | Satellite center | IGS05 PCV model applied. | | of mass | | | correction | | |---------------------------------------------------------------------------| | Satellite phase | IGS05 PCV model applied. | | center calibrat. | | ----------------------------------------------------------------------------- | Time argument | TDT | ----------------------------------------------------------------------------- | GNSS attitude | Not applied | | model | | ----------------------------------------------------------------------------- ----------------------------------------------------------------------------- | ORBIT MODELS | |---------------------------------------------------------------------------| | Geopotential | JGM3 model up to degree and order 12 (+C21+S21) | | |--------------------------------------------------------| | | GM = 398600.4415 km**3/sec**2 | | |--------------------------------------------------------| | | AE = 6378.1363 km | |---------------------------------------------------------------------------| | Third-body | Sun and Moon as point masses | | |--------------------------------------------------------| | | Ephemeris: JPL DE200 | | |--------------------------------------------------------| | | GMsun = 132712500000 km**3/sec**2 | | |--------------------------------------------------------| | | GMmoon = 4902.7890 km**3/sec**2 | |---------------------------------------------------------------------------| | Solar radiation | Direct radiation: CODE RPR model coefficients | | pressure | (updated 2007) | | |--------------------------------------------------------| | | Estimated RPR parameters : | | | Constants in D-, Y- and X-direction | | | Periodic terms in X-direction | | |--------------------------------------------------------| | | Earth shadow model includes: cylindric shadow | | |--------------------------------------------------------| | | Moon shadow model includes: umbra and penumbra | | |--------------------------------------------------------| | | Reflection radiation: not included | | |--------------------------------------------------------| | | New GPS satellite attitude model: not applied | |---------------------------------------------------------------------------| | Tidal forces | Solid earth tides: TIDE2000 (IERS 2000) | | |--------------------------------------------------------| | | Ocean tides: OT CSR30 model, plus TEG-2B | |---------------------------------------------------------------------------| | Relativity | Applied (IERS 2003) | |---------------------------------------------------------------------------| | Numerical | Integration algorithms developed at AIUB by Gerhard | | Integration | Beutler. Representation of the orbit by a | | | polynomial of degree 10 for 1 hour. | | |--------------------------------------------------------| | | Integration step: 1 hour | | |--------------------------------------------------------| | | Starter procedure: no special starter procedure needed | | |--------------------------------------------------------| | | Arc length: 27 hours, plus extrapolation to create | | | 48-hr orbit. | ----------------------------------------------------------------------------- ----------------------------------------------------------------------------- | ESTIMATED PARAMETERS (APRIORI VALUES & SIGMAS) | |---------------------------------------------------------------------------| | Adjustment | Weighted least-squares algorithms | |---------------------------------------------------------------------------| | Station | Starting with GPS week 1400, the IGS realization of | | coordinates | ITRF2005 (IGS05) is used, but IGS05 PCV values not | | | applied until 12 Jun 2008. Between Nov 2006 and Jun | | | 2008, IGS01 PCV values used instead. | |---------------------------------------------------------------------------| | Satellite clock | Zero-difference data analysis for GPS clock estimation:| | | | | | Satellite clock corrections are computed | | | on the basis of the double-difference orbit, ERP, | | | coordinate, and troposphere solutions. The generation | | | of clock results is performed via least-squares | | | adjustment with a sampling rate of 5 min | | | using phase and code observations. | |---------------------------------------------------------------------------| | Orbital | 6 Keplerian elements plus constant D- (direct solar | | parameters | radiation pressure) and Y- (y-bias) terms | | | at start of arc; no a priori sigmas used. | | | | | | Previous IGS ultra-rapid orbits are used as a priori | | | solutions. | |---------------------------------------------------------------------------| | Troposphere | Zenith delay parameters and pairs of horizontal delay | | | gradient parameters are estimated for each station in | | | intervals of 2 hours and 24 hours. No a priori | | | constraints are applied. Piece-wise, linear | | | parameterization. | |---------------------------------------------------------------------------| | Ionospheric | Not estimated in ionosphere-free analyses | | correction | | |---------------------------------------------------------------------------| | Ambiguity | Ambiguities are resolved in a baseline-by-baseline | | | mode using the SIGMA approach, first with L5 (widelane)| | | then with L3 (narrowlane). | |---------------------------------------------------------------------------| | Earth Orient. | X- and Y-pole coordinates, and UT1-UTC are represented | | Parameters (EOP) | each with piece-wise linear polynomials which are | | | continuous in time. UT1-UTC is fixed to the a priori | | | value at the beginning of the first day. | |---------------------------------------------------------------------------| | GNSS attitude | Not estimated | | model | | |---------------------------------------------------------------------------| ----------------------------------------------------------------------------- | REFERENCE FRAMES | |---------------------------------------------------------------------------| | Inertial | Geocentric; mean equator and equinox of 2000 Jan 1 | | | at 12:00 (J2000.0) | |---------------------------------------------------------------------------| | Terrestrial | IGS05 station coordinates and velocities | |---------------------------------------------------------------------------| | Interconnection | Precession: IAU 2000 Precession Theory | | |--------------------------------------------------------| | | Nutation: IAU 2000 Nutation Theory | | |--------------------------------------------------------| | | Tidal variations in UT1: periods > 5.8 days modeled | | | but not removed (UT1-UTC sol.)| -----------------------------------------------------------------------------