MIT ANALYSIS
STRATEGY SUMMARY (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 email: tah@mit.edu
phone : ++ 1 617 253 5941 Robert King
email: rwk@chandler.mit.edu
phone : ++ 1 617 2537064 Simon McClusky
email: simon@mit.edu
phone : ++ 1 617 2537944 
Software used 
GAMIT v. 10.32, GLOBK v. 5.12 
GNSS system(s) 
GPS 
Final products generated
for GPS Week 'WWWW' day
of Week 'n' (n=0,1,...,6) 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
6hour overlap with surronding days. mitwwww7.erp ERP (pole, UT1UTC) 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 
20080229 (original updated version) 
Modification dates 

Effective date for
data analysis 
20061105 (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. 



MEASUREMENT MODELS 

Preprocessing 
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, ionospherefree combination of L1 and L2 carrier phases. Pseudoranges
are used only to obtain receiver clock offsets and in ambiguity resolution MelbourneWuebbena widelane method. Nonredundant double differences are
used [Schaffrin and Bock, 1988] 
Elevation angle cutoff: 10 degrees Sampling rate: 30
seconds for cleaning; 2 minutes in leastsquares analysis. Code biases: C1 & P2' corrected to P1 & P2
using receiver type dependent monthly tables from http://www.aiub.unibe.ch/ionosphere/p1c1.dcb 

Modeled observables 
Doubledifferenced carrier phase with ionospherefree
linear combination applied.
Clocks are estimated in a postprocessing step using oneway
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 offsets 
SVspecific zoffsets & blockspecific x &
yoffsets (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 corrections 
Blockspecific nadir angledependent
"absolute" PCVs applied from file
igs05_wwww.atx; no azimuthdependent corrections applied [refer to IGS Mail
#5189, 17 Aug 2005] 
*Satellite clock corrections 
2nd order relativistic correction for nonzero orbit ellipticity (2*R*V/c) applied [NOTE: other dynamical
relativistic effects under Orbit Models] 
GPS attitude model 
GPS satellite yaw attitude model: applied (BarSever,
1995) based on nominal yaw rates 
*RHC phase rotation
corrections 
Phase windup
applied according to Wu et al. (1993) 
*Ground antenna phase
center offsets
& corrections 
"Absolute" elevation & azimuthdependent
(when available) PCVs & L1/L2 offsets from ARP
applied from file igs05_wwww.atx [refer to IGS Mail #5189, 17 Aug 2005] 
*Antenna radome calibrations 
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 
Troposphere 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 

Ionosphere 
1st order effect: accounted for by dualfrequency
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: zerofrequency 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
sitedependent amps & phase for 11 main tides from Bos
& Scherneck website for FES2004 model; CMC
corrections applied to SP3 orbits. 

Ocean tide geocenter:
sitedependent 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] 

Nontidal loadings 
Atmospheric
pressure: not applied 
Ocean bottom pressure:
not applied 

Surface hydrology:
not applied 

Other effects: none
applied 

Earth orientation Variations 
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] 

Highfrequency 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] 



REFERENCE FRAMES 

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 (J2000.0) 
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 4sigma 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. 
Interconnection (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) 



ORBIT MODELS 

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 orderdependent 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 

Thirdbody 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 blockdependent constant direct acceleration; corrections to
direct, yaxis, and Baxis constant and onceperrev 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 BarSever (1995) applied; using nominal yaw rates 

Other forces: none applied 

Relativitic effects 
Dynamical
correction: not applied (see IERS 2003, Ch. 10, eqn
1) 
Gravitational time
delay: IERS 2003, Ch. 11, eqn 17 applied 

Numerical integration 
AdamsMoulton
fixedstep, 11pt predictorcorrector with Nordsieck
variablestep starting procedure (see Ash, 1972 and references therein) 
Integration
stepsize: 75 s; tabular interval: 900 s 

Starter procedure: RungeKutta Formulation; initial
conditions taken from prior orbit solution at 12:00 

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



ESTIMATED PARAMETERS
(& APRIORI VALUES & CONSTRAINTS) 



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 nonetrotation 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
oneway 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 30sec sampling for
clock files. 

Receiver clocks 
Estimated during
clock estimation. Stations clocks
except the reference clock station are decimated to 300 seconds. 
Orbits 
Geocentric position and velocity, solar radiation
pressure scales and onceperrevolution 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 oneday arc; plus
onceper rev sine/cosine terms are estimated with apriori values from the
prior day, and weak apriori constraints. 
sp3 files: orbits transformed to crustfixed (rotating) frame accounting
for geocenter motions due to ocean tides and for subdaily tidal EOP variations 

Satellite attitude 
No attitude
parameters are adjusted 
Troposphere 
Zenith delay: residual delays are adjusted for each
station assuming mostly dominated by "wet" component; parameterized
by piecewise linear, continuous model with 2hr intervals 
Mapping function: GMF (Boehm et al., 2006) wet function
used to estimate zenith delay residuals 

Zenith delay epochs:
each eveninteger hour 

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

Ionospheric correction 
not estimated 
Ambiguity 
Realvalued doubledifferenced phase cycle ambiguities
adjusted except when they can be resolved confidently in which case they are
fixed using the MelbourneWebana widelane to resolve L1L2 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, polerates, and LOD at
noon epochs; x and y pole estimated as piecewise, linear offsets from IERS
Bulletin A a prioris over
each 1day segment. UT1 is
estimated with tight constraints on the first day. 
Other parameters 
none 


REFERENCES Ash,
M. E., Determination of Earth satellite orbits, Tech. Note 19725, Lincoln
Laboratory, MIT, 19 April 1972. BarSever, Y.E., New GPS attitude model, IGS Mail #591,
1995, http://igscb.jpl.nasa.gov/mail/igsmail/1994/msg00166.html 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, 367386, 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/s0019000701353, 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,
39493966, 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, 200214, 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), 170180, 2004. Niell, A. E., Global mapping functions for the atmospheric delay, J. Geophys. Res., 101, 32273246, 1996. Ray, R.D.,
ftp://maia.usno.navy.mil/conventions/chapter8/ray.f (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.247251, 1972. Schaffrin, B., and Y.
Bock, A unified scheme for processing GPS phase observations, Bulletin Geodesique, 62, 142160, 1988. Springer, T. A., G. Beutler,
and M. Rothacher, A new solar radiation pressure
model for the GPS satellites, IGS Analysis Center Workshop, Darmstadt, 911
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, 9198, 1993. 