(template version 2.0, 12 Feb. 2008)

Analysis Center

Massachusetts Institute of Technology (MIT)

77 Massachusetts Av, Cambridge, MA 02139

Phone:  ++ 1 617 253 5941

Fax:    ++ 1 617 258 7401

Contact people

Thomas Herring           e-mail:

                         phone : ++ 1 617 253 5941

Robert King              e-mail:

                         phone : ++ 1 617 253-7064

Simon McClusky           e-mail:

                         phone : ++ 1 617 253-7944

Software used

GAMIT v. 10.32, GLOBK v. 5.12

GNSS system(s)


Final products

generated for


day of Week 'n'



Rapid products

generated daily

mitwwwwn.sp3    GPS ephemeris files in 7 daily

                files at 15 min intervals in SP3 format,

                including accuracy codes computed from

                6-hour overlap with surronding days.

mitwwww7.erp    ERP (pole, UT1-UTC) weekly solution

mitwwww7.sum    Summary of weekly solution.

mitwwww7.snx    Weekly coordinates in SINEX format

mitwwwwn.clk    Station and satellite clock solutions. 30 second interval for satellites and reference site. 15 minutes for other sites.


Preparation date

2008-02-29 (original updated version)

Modification dates


Effective date

for data analysis

2006-11-05 (GPS week 1400) and afterwards, including IGS reanalysis campaign

Instructions: Please provide as complete information as possible. The template below is illustrative only; replies should reflect actual analysis implementation. Please accumulate changes with effective dates of usage, rather than remove earlier information.





Networks are selected based on available rinex data files and a core list of 117 clock and igs reference sites.  Small rinex files (less than 3hrs of data) are rejected. 250 sites processed daily.


Basic observables

Doubly differenced, ionosphere-free combination of L1 and L2 carrier phases.  Pseudoranges are used only to obtain receiver clock offsets and in ambiguity resolution Melbourne-Wuebbena widelane method.  Non-redundant double differences are used [Schaffrin and Bock, 1988]

Elevation angle cutoff:  10 degrees

Sampling rate:           30 seconds for cleaning; 2 minutes in least-squares analysis.

Code biases: C1 & P2' corrected to P1 & P2 using receiver type dependent monthly tables from 



Double-differenced carrier phase with ionosphere-free linear combination applied.  Clocks are estimated in a post-processing step using one-way observables with the ensemble mean of the clock residuals at a set of reference ground stations set to zero at each epoch. 

*Satellite antenna

-center of mass


SV-specific z-offsets & block-specific x- & y-offsets (from manufacturers) from file igs05_wwww.atx based on GFZ/TUM analyses using fixed ITRF2000 coordinates [refer to IGS Mail #5189, 17 Aug 2005]

*Satellite antenna

phase center


Block-specific nadir angle-dependent "absolute" PCVs applied from file igs05_wwww.atx; no azimuth-dependent corrections applied [refer to IGS Mail #5189, 17 Aug 2005]

*Satellite clock


2nd order relativistic correction for non-zero orbit ellipticity (-2*R*V/c) applied [NOTE: other dynamical relativistic effects under Orbit Models]

GPS attitude model

GPS satellite yaw attitude model: applied (Bar-Sever, 1995) based on nominal yaw rates

*RHC phase

rotation corrections

Phase wind-up applied according to Wu et al. (1993)

*Ground antenna

phase center

offsets &


"Absolute" elevation- & azimuth-dependent (when available) PCVs & L1/L2 offsets from ARP applied from file igs05_wwww.atx [refer to IGS Mail #5189, 17 Aug 2005]

*Antenna radome


Calibration applied if given in file igs05_wwww.atx; otherwise radome effect neglected (radome => NONE)

*Marker -> antenna

ARP eccentricity

dN,dE,dU eccentricities from site logs applied to compute station marker coordinates


a priori model



(parameter estimation

is below)

Met data input: latitude, longitude, height, DOY climate model from Boehm et al. (2007) (GPT version 2006June16); rel. humidity set to 50% for all sites

Zenith delay: Saastamoinen (1972) "dry" + "wet" using synthesized input met data

Mapping function: GMF (Boehm et al., 2006) for dry & wet zenith delays individually

Horiz. grad. model: no a priori gradient model is used


1st order effect: accounted for by dual-frequency observations in linear combination

2nd order effect: no corrections applied

Other effects:    no corrections applied

Tidal Displacements


(IERS Conventions

2003, Ch. 4, eqn 11)

Solid Earth tide: IERS 2003

Permanent tide: zero-frequency contribution left in tide model, NOT in site coordinates

Solid Earth pole tide: IERS 2003; mean pole removed by linear trend (Ch. 7, eqn 23a & 23b)

Oceanic pole tide: no model is applied    [IERS Conventions updated, Ch. 7, eqn 27]

Ocean tide loading: IERS Conventions 2003 (updated    Ch. 7, 2006) using site-dependent amps & phase for 11 main tides from Bos & Scherneck website for FES2004 model; CMC corrections applied to SP3 orbits.

Ocean tide geocenter: site-dependent coeffs corrected for center of mass motion of whole Earth; CMC corrections also applied to SP3 orbits.

Atmosphere tides: corrections for S1 & S2 tidal pressure loading not applied (no model available yet) [IERS model under development]

Non-tidal loadings

Atmospheric pressure:  not applied

Ocean bottom pressure: not applied

Surface hydrology:     not applied

Other effects:         none applied

Earth orientation



Ocean tidal: diurnal/semidiurnal variations in x,y, & UT1 applied according to IERS 2003.

Atmosphere tidal: S1, S2, S3 tides not applied [no IERS model specified yet]

High-frequency nutation: prograde diurnal polar motion corrections (IERS 2003, Table 5.1) applied using IERS routine.

[NOTE: effects are included in observation model as well as in the transformation of orbits from inertial to terrestrial frame]




Time argument

GPS time as given by observation epochs, which is offset by only a fixed constant (approx.) from TT/TDT

Inertial frame

Geocentric; mean equator and equinox of 2000 Jan 1.5


Terrestrial frame

ITRF2005 reference frame realized through the set of up to 132 station coordinates and velocities given in the IGS internal realization IGS05.snx (aligned to ITRF2005).  Reference sites may be removed from the realization if the standard deviation of their position estimates deviates too much from the median sigma of the remaining reference sites or if their position estimate deviates by more than 4-sigma from the apriori value.  Conditions are applied iteratively. The datum for Finals is specified only for orientation using NNR constraints wrt IGS05 coordinates.

Tracking network

Tracking network is based on 117 clock sites as specified by the type of clock plus an additional 208 sites that fill out the core list of sites.  Six global distributed networks of ~50 sites each, with two overlap sites between each pair of networks, form a global network of 243 stations that are dynamically selected based on available data.



(EOP parameter

estimation is below)

Precession: IAU 1976 Precession Theory

Nutation: IAU 2000A Nutation Theory

A priori EOPs: polar motion & UT1 interpolated from IERS Bulletin A, updated weekly, with the restoration of subdaily EOP variations using IERS models (see MODELS above)




Geopotential (static)

EGM96 degree and order 9; C21 & S21 modeled according to polar motion variations (IERS 2003, Ch. 6)

GM=398600.4415 km**3/sec**2 (for TT/TDT time argument)

AE = 6378136.3 m

Tidal variations in geopotential

Solid Earth tides: C20,C21,S21,C22, and S22 as in IERS (1992); n=2 order-dependent Love numbers & frequency dependent corrections for 6 (2,1) tides from Richard Eanes (private comm., 1995)

Ocean tides: none

Solid Earth pole tide: None applied in orbit models

Oceanic pole tide: no model applied

Third-body forces

Sun & Moon as point masses

Ephemeris: Generated from the MIT PEP program

GM_Sun    132712440000.0000  km**3/sec**2

GM_Moon           4902.7989  km**3/sec**2

Solar radiation  pressure model


(parameter estimation is below)

A priori: nominal block-dependent constant direct acceleration; corrections to direct, y-axis, and B-axis constant and once-per-rev terms estimated (Beutler et al., 1994; Springer et al. 1998)

Earth shadow model: umbra & penumbra included

Earth albedo:       not applied

Moon shadow:        umbra & penumbra included

Satellite attitude: model of Bar-Sever (1995) applied;  using nominal yaw rates

Other forces:       none applied



Dynamical correction: not applied (see IERS 2003, Ch. 10, eqn 1)

Gravitational time delay: IERS 2003, Ch. 11, eqn 17 applied

Numerical integration

Adams-Moulton fixed-step, 11-pt predictor-corrector with Nordsieck variable-step starting procedure (see Ash, 1972 and references therein)

Integration step-size: 75 s; tabular interval: 900 s

Starter procedure: Runge-Kutta Formulation; initial conditions taken from prior orbit solution at 12:00

Arc length: 24 hours (00:00:00 - 23:59:30 GPS time)





Adjustment method

Weighted least squares to generate loosely constrained covariance matrices and solutions that are passed to a Kalman filter for network combinations and weekly combinations for orbit determination

Data span

24 hours used for each daily analysis

(00:00:00 - 23:59:30 GPS time)

Station coordinates

All station coordinates are adjusted, relative to the a priori values from IGS05.snx; a no-net-rotation condition is applied wrt the IGS05 frame using up to 132 reference frame stations; apriori sigmas for all stations are 10 m for each component.

Satellite clocks

Estimated using one-way phase data aligned with pseudorange.  Time reference is defined by an ensemble average over selected hydrogen maser sites fit to broadcast ephemeris clocks.  Clock estimation is completed after orbits and station coordinates for a week of data have been determined.

sp3,clock files: Estimated values included 30-sec sampling for clock files.

Receiver clocks

Estimated during clock estimation.  Stations clocks except the reference clock station are decimated to 300 seconds.


Geocentric position and velocity, solar radiation pressure scales and once-per-revolution perturbation terms. Radiation pressure scaling factors and perturbation terms are estimated for each of the orthogonal directions: satellites - sun, body centered Y, and orthogonal third directions estimated as constant offsets for each one-day arc; plus once-per- rev sine/cosine terms are estimated with apriori values from the prior day, and weak apriori constraints.

sp3 files: orbits transformed to crust-fixed (rotating) frame accounting for geocenter motions due to ocean tides and for subdaily tidal EOP variations

Satellite attitude

No attitude parameters are adjusted


Zenith delay: residual delays are adjusted for each station assuming mostly dominated by "wet" component; parameterized by piecewise linear, continuous model with 2-hr intervals

Mapping function: GMF (Boehm et al., 2006) wet function used to estimate zenith delay residuals

Zenith delay epochs: each even-integer hour

Gradients: two N-S & two E-W gradient parameter per day for each station, with linear variation during the day; 30mm at 10-deg elevation 1-sigma constraint is applied at all stations.  Mapping function from Chen and Herring (1997) used. 

Ionospheric correction

not estimated


Real-valued double-differenced phase cycle ambiguities adjusted except when they can be resolved confidently in which case they are fixed using the Melbourne-Webana widelane to resolve L1-L2 cycles and then estimation to resolve L1 and L2 cycles.  About 95% of all ambiguities are fixed using modern network data

*Earth orientation

parameters (EOP)

Daily x & y pole offsets, pole-rates, and LOD at noon epochs; x and y pole estimated as piece-wise, linear offsets from IERS Bulletin A a prioris over each 1-day segment.  UT1 is estimated with tight constraints on the first day. 

Other parameters





Ash, M. E., Determination of Earth satellite orbits, Tech. Note 1972-5, Lincoln Laboratory, MIT, 19 April 1972.

Bar-Sever, Y.E., New GPS attitude model, IGS Mail #591, 1995,

Beutler, G., E. Brockmann, W. Gurtner, U. Hugentobler, L. Mervart, and M. Rothacher, 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.

Boehm, J., A.E. Niell, P. Tregoning, & H. Schuh, Global Mapping Function (GMF): A new empirical mapping function based on numerical weather model data, Geophys. Res. Lett., 33, L07304, doi: 10.1029/2005GL025545, 2006.

Boehm, J., R. Heinkelmann, & H. Schuh, Short Note: A global model of pressure and temperature for geodetic applications, J. Geod., doi:10.1007/s00190-007-0135-3, 2007.

Chen, G. and T. A. Herring, Effects of atmospheric azimuthal asymmetry of the analysis of space geodetic data, J. Geophys. Res., 102, 20,489–20,502, 1997

Dong, D., and Y. Bock, Global Positioning System network analysis with phase ambiguity resolution applied to crustal deformation studies in California, Journal of Geophysical Research, 94, 3949-3966, 1989.

Dong, D., T. A. Herring, and R. W. King, Estimating Regional Deformation from a Combination of Space and Terrestrial Geodetic Data, J. Geodesy, 72, 200-214, 1998.

IERS Conventions 2003, D.D. McCarthy & G. Petit (editors), IERS Technical Note 32, Frankfurt am Main: Verlag des Bundesamts fuer Kartographie und Geodaesie, 2004.  (see also updates at website)

Kouba, J., Improved relativistic transformations in GPS, GPS Solutions, 8(3), 170-180, 2004.

Niell, A. E., Global mapping functions for the atmospheric delay, J. Geophys. Res., 101, 3227-3246, 1996.

Ray, R.D., (IERS Standards), 1995

Saastamoinen, J., Atmospheric correction for the troposphere and stratosphere in radio ranging of satellites, in The Use of Artificial Satellites for Geodesy, Geophys. Monogr. Ser. 15 (S.W. Henriksen et al., eds.), AGU, Washington, D.C., pp.247-251, 1972.

Schaffrin, B., and Y. Bock, A unified scheme for processing GPS phase observations, Bulletin Geodesique, 62, 142-160, 1988.

Springer, T. A., G. Beutler, and M. Rothacher, A new solar radiation pressure model for the GPS satellites, IGS Analysis Center Workshop, Darmstadt, 9-11 February 1998.

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