============================================================================= | EMR ANALYSIS STRATEGY SUMMARY | | (template version 2.0, 25 June 2008) | ============================================================================= | Analysis Center | Natural Resources Canada (emr) | | | EMR | | | 615 Booth St, Ottawa, Canada, K1A 0E9 | | | Phone: 1 613 947 4246 | | | Fax: 1 613 992 4605 | |---------------------------------------------------------------------------| | Contact people | Brian Donahue(1) email: bdonahue@nrcan.gc.ca | | | Pierre Tetreault(1) email: ptetreau@nrcan.gc.ca | | | Yves Mireault(2) email: ymireaul@nrcan.gc.ca | | | (1) for final,rapid, and IGS reanalysis products | | | (2) for ultra-rapid products | |---------------------------------------------------------------------------| | Software used | GIPSY/OASISII V5, developed by JPL | |---------------------------------------------------------------------------| | GNSS system(s) | GPS | |---------------------------------------------------------------------------| | IGS products | emrwwwwn.sp3 daily orbit files | | generated for | emrwwww7.erp weekly ERP file of daily values | | GPS Week 'wwww' | emrwwwwn.clk daily station & SV clock files | | day of Week 'n' | emrwwww7.sum weekly summary file | | (n=0,1,...,6) | emrwwww7.snx weekly SINEX file | | | emrwwwwn.tro daily tropo files | | | | | | | |---------------------------------------------------------------------------| | Preparation date | 2008-07-31 | |---------------------------------------------------------------------------| | Modification dates| 2009-10-11: subdaily eop model IERS96 --> IERS03 | | | | |---------------------------------------------------------------------------| | Effective date | 2008-08-11 (emr Final) & reanalysis | | for data analysis | | |---------------------------------------------------------------------------| ============================================================================= ============================================================================= | MEASUREMENT MODELS | |---------------------------------------------------------------------------| | Preprocessing | RINEX files pre-screened using PPP metrics to reject | | | small/incomplete files (<50%), excessive phase slips | | | (>500), or large phase residuals (>1cm); | | | Code rejected for rinex files with large code | | | residuals (>1m) | | | outliers edited & cycle slips detected/fixed; | | | 1 ms RINEX clock jumps fixed using clockprep; | | | code biases corrected to P1/P2 using cc2noncc; | | | | |---------------------------------------------------------------------------| | Basic observables| undifferenced carrier phase & smoothed pseudorange | | |--------------------------------------------------------| | | elevation angle cutoff: 10 degrees | | | sampling rate: 5 minutes | | | weighting: carrier phase= 1 cm sigma (nominally) | | | pseudorange= 1 m sigma (nominally) | | | sigmas increase with decreasing elevation | | | angle | | | deweighting: station specific based on PPP results | | | smoothing: carrier smoothed pseudoranges | | | code biases: C1 & P2' corrected to P1 & P2 using | | | cc2noncc tool depending on receiver type | |---------------------------------------------------------------------------| | Modeled | undifferenced, corrected for 1st order ionosphere | | observables | effect to LC & PC | |---------------------------------------------------------------------------| |*Satellite antenna| SV-specific z-offsets & block-specific x- & y-offsets | | -center of mass | (from manufacturers) from file igs05_wwww.atx based on | | offsets | GFZ/TUM analyses using fixed ITRF2000 coordinates | | | [refer to IGS Mail #5189, 17 Aug 2005] | |---------------------------------------------------------------------------| |*Satellite antenna| block-specific nadir angle-dependent "absolute" PCVs | | phase center | applied from file igs05_wwww.atx; no azimuth-dependent | | corrections | corrections applied | | | [refer to IGS Mail #5189, 17 Aug 2005] | |---------------------------------------------------------------------------| |*Satellite clock | 2nd order relativistic correction for non-zero | | corrections | orbit ellipticity (-2*R*V/c) applied | | | [NOTE: other dynamical relativistic effects under | | | Orbit Models] | |---------------------------------------------------------------------------| | GPS attitude | GPS satellite yaw attitude model: applied (Bar-Sever, | | model | 1995); yaw rates adjusted as described below | |---------------------------------------------------------------------------| |*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 from | | offsets & | file igs05_wwww.atx | | corrections | [refer to IGS Mail #5189, 17 Aug 2005] | |---------------------------------------------------------------------------| |*Antenna radome | calibration applied if given in file igs05_wwww.atx; | | calibrations | otherwise radome effect neglected (radome => NONE) | |---------------------------------------------------------------------------| |*Marker -> antenna| dN,dE,dU eccentricities from site logs applied to | | ARP eccentricity | compute station coordinates | |---------------------------------------------------------------------------| | Troposphere | zenith delay: VMF1 | | a priori model | | | |--------------------------------------------------------| | (parameter | mapping function: GMF (Boehm et al., 2006) for dry | | estimation is | & wet zenith delays individually | | below) | | | |--------------------------------------------------------| | | gradient model: Horizontal gradients estimated as | | | described below | |---------------------------------------------------------------------------| |*Ionosphere | 1st order effect: accounted for by dual-frequency | | | observations in linear combination | | |--------------------------------------------------------| | | 2nd order effect: no corrections applied | | |--------------------------------------------------------| | | other effects: no corrections applied | |---------------------------------------------------------------------------| |*Tidal |*solid Earth tide: IERS 2003 | | displacements |--------------------------------------------------------| | |*permanent tide: zero-frequency contribution left in | | (IERS Conventions| tide model, NOT in site coordinates | | 2003, Ch. 4, eqn |--------------------------------------------------------| | 11) |*solid Earth pole tide: IERS 2003; mean pole removed | | | by linear trend (Ch. 7, eqn 23a & 23b) | | |--------------------------------------------------------| | |*oceanic pole tide: None applied | | | | | |--------------------------------------------------------| | |*ocean tide loading: consistent with IERS 2003 (Ch. 7), | | | site-dependent amps & phases from Bos | | | & Scherneck website for FES2004 tide | | | model | | | | | |--------------------------------------------------------| | |*ocean tide geocenter: coeffs corrected for center of | | | mass motion of whole Earth; CMC | | | corrections also applied to SP3 | | | | | |--------------------------------------------------------| | | atmosphere tides: corrections for S1 & S2 tidal | | | pressure loading not applied (no model | | | available yet) | | | [IERS model under development] | |---------------------------------------------------------------------------| |*Non-tidal | atmospheric pressure: not applied | | loadings |--------------------------------------------------------| | | ocean bottom pressure: not applied | | |--------------------------------------------------------| | | surface hydrology: not applied | | |--------------------------------------------------------| | | other effects: none applied | |---------------------------------------------------------------------------| |*Earth orientation| ocean tidal: diurnal/semidiurnal variations in x,y, & | | variations | UT1 applied according to IERS 2003 | | |--------------------------------------------------------| | (near 12 & 24 hr | atmosphere tidal: S1, S2, S3 tides not applied | | only; longer | [no IERS model specified yet] | | period tidal |--------------------------------------------------------| | corrections | high-frequency nutation: not applied | | should not be | | | applied) | | | |--------------------------------------------------------| | | | [NOTE: effects should be 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 | geocentric; mean equator and equinox of 2000 Jan 1.5 | | frame | (J2000.0) | |---------------------------------------------------------------------------| | Terrestrial | ITRF2005 reference frame realized through the set of up| | frame | to 132 station coordinates and velocities given in the | | | IGS internal realization IGS05_061023.snx | | | | |---------------------------------------------------------------------------| | Tracking | 75 daily stations dynamically selected based on | | network | geometry with priority on 132 global reference frame | | | stations. Stations are processed in 1 global network. | | | | |---------------------------------------------------------------------------| | Interconnection | precession: IAU 1976 Precession Theory | | |--------------------------------------------------------| | (EOP parameter | nutation: IAU 1980 Nutation Theory. | | estimation is | | | below) | | | | | | |--------------------------------------------------------| | | 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 | JGM-3 to degree & order 12; C21 & S21 modeled according| | (static) | to polar motion variations (IERS 2003, Ch. 6) | | |--------------------------------------------------------| | | GM=398600.4415 km**3/sec**2 (for TT/TDT time argument) | | | | | |--------------------------------------------------------| | | AE = 6378136 m | |---------------------------------------------------------------------------| | Tidal variations |*solid Earth tides: IERS 2003 | | in geopotential | | | |--------------------------------------------------------| | | ocean tides: IERS 2003 | | | | | |--------------------------------------------------------| | |*solid Earth pole tide: IERS 2003 | | |--------------------------------------------------------| | | oceanic pole tide: IERS 2003 | | | | | | | |---------------------------------------------------------------------------| | Third-body | Sun, Moon, Mercury, Venus, Mars, Jupiter, Saturn, | | forces | Uranus, Neptune (regarded as point masses) | | |--------------------------------------------------------| | | ephemeris: JPL DE405 | | |--------------------------------------------------------| | | GM_Sun 132712440017.9870 km**3/sec**2 | | | Moon-Earth mass ratio 0.012300038 | | | Sun-Mercury mass ratio 6023600. | | | Sun-Venus mass ratio 408523.71 | | | Sun-Mars mass ratio 3098708. | | | Sun-Jupiter mass ratio 1047.3486 | | | Sun-Saturn mass ratio 3497.898 | | | Sun-Uranus mass ratio 22903. | | | Sun-Neptune mass ratio 19412.24 | |---------------------------------------------------------------------------| | Solar radiation | a priori: GSPM_EPS model of Bar-Sever | | pressure model | | | | | | (parameter |--------------------------------------------------------| | estimation is | Earth shadow model: umbra & penumbra included | | below) |--------------------------------------------------------| | | Earth albedo: not applied | | |--------------------------------------------------------| | | Moon shadow: not applied | | |--------------------------------------------------------| | | satellite attitude: model of Bar-Sever (1995) applied; | | | yaw rates estimated as described below | | |--------------------------------------------------------| | | other forces: none applied | |---------------------------------------------------------------------------| |*Relativitic | dynamical correction: not applied | | effects | | | |--------------------------------------------------------| | | gravitational time delay: IERS 2003, Ch. 11, eqn 17 | | |--------------------------------------------------------| |---------------------------------------------------------------------------| | Numerical | variable (high) order Adams predictor-corrector | | integration | with direct integration of second-order equations | | |--------------------------------------------------------| | | integration step: variable | | |--------------------------------------------------------| | | starter procedure: Runge-Kutta | | |--------------------------------------------------------| | | arc length: 24 hours | ============================================================================= ============================================================================= | ESTIMATED PARAMETERS (& APRIORI VALUES & CONSTRAINTS) | |---------------------------------------------------------------------------| | Adjustment | square-root information filter (SRIF) [Bierman, 1977] | | method | | |---------------------------------------------------------------------------| | Data span | 24 hours used for each daily analysis | | | | |---------------------------------------------------------------------------| |*Station | all station coordinates are adjusted, relative to the | | coordinates | a priori values from IGS05_061023.snx. The IGS05 vel. | | | are used for daily coordinate updates. | |---------------------------------------------------------------------------| | Satellite clocks | solved for at each epoch as white noise process with a | | | steady state sigma of 1 ms | | |--------------------------------------------------------| | | sp3,clk files: frame for clocks corresponds to ITRF | | | origin by applying 3 translations to | | | satellite clocks based on daily | | | alignment to IGS05 | |---------------------------------------------------------------------------| | Receiver clocks | solved for at each epoch as white noise process with a | | | steady state sigma of 1 ms; one station clock fixed & | | | used as a timescale reference, usually ALGO or AMC2. | | | | | | Output .clk file of clock products has been "densified"| | | using PPP with our own satellite orbit/clock files to | | | generate clocks for stations not used in the orbit/TRF | | | solution. Highest priority is given to stations with | | | stable clocks and stations co-located at time labs. | |---------------------------------------------------------------------------| | Orbits | initial positions and velocities, y-bias, solar | | | radiation pressure scale in direct direction; | | | stochastic y_bias and x/z solar scale with | | | steady state sigma of 0.02e-12 km/s/s and correlation | | | time of 4 hrs solved for every hour. nominally | | | initial velocity sigma increased for eclipsing SV | | |--------------------------------------------------------| | | sp3 files: orbits transformed to crust-fixed (rotating)| | | frame accounting for geocenter motions due | | | to ocean tides and for subdaily tidal EOP | | | variations | |---------------------------------------------------------------------------| | Satellite | deterministic yaw bias with yaw rates estimated as | | attitude | white noise for satellites which are eclipsing with | | | a steady state sigma of 0.01 deg/sec, solved for every | | | 6 hours | |---------------------------------------------------------------------------| | Troposphere | zenith delay: estimated for each observation epoch as | | | a random walk with process noise of | | | 3.0 mm/sqrt(hr) | | |--------------------------------------------------------| | | mapping function: GMF (Boehm et al., 2006) | | |--------------------------------------------------------| | | zenith delay epochs: each observation epoch | | |--------------------------------------------------------| | | gradients: one N-S and one E-W gradient parameter | | | estimated for each epoch as a random walk| | | with process noise of 0.3 mm/sqrt(hr) | |---------------------------------------------------------------------------| | Ionospheric | not estimated | | correction | | |---------------------------------------------------------------------------| | Ambiguity | real valued phase cycle ambiguities adjusted except | | | when double-differenced ambiguities can be resolved. | | | About 65% of ambiguities resolved. | |---------------------------------------------------------------------------| |*Earth orientation| daily x & y pole offsets, pole-rates, and LOD at noon | | parameters (EOP) | epochs; LOD loosely constrained to 32.2 mas/day; | | | UT1 is estimated with tight constraints | |---------------------------------------------------------------------------| | Other | none | | parameters | | ============================================================================= ============================================================================= | NOTES ON HANDLING OCEAN TIDAL LOADING DISPLACEMENT EFFECTS | |---------------------------------------------------------------------------| | There are three main parts involved in implementing model corrections for | | ocean tidal loading (OTL) effects in GPS analyses to be fully self- | | consistent: | | [1] Site-dependent tidal coefficients | | Site-dependent amplitude & phase values for the 11 main tides (in BLQ | | format) are generated upon request by the Bos-Scherneck OTL service at | | http://www.oso.chalmers.se/~loading/ | | Users are advised to select one of the more modern ocean models from the | | list available, such as FES2004 models. | | For the option "Do you want to correct your loading values for the [center| | of mass] motion?" the answer should be "YES" (but the default is "NO"). | | [Note that for users of IGS orbits (in sp3 format) it is generally *not* | | necessary to consider the center of mass effect because this has already | | been taken into account by the IGS (see below). That is, the IGS orbits | | are expressed with respect to the Earth's crust as a fixed frame. So, for| | such applications, site-dependent coefficients should be with the option | | "Do you want to correct your loading values for the motion?" set to the | | default "NO".] | | [2] Site-dependent tidal displacements | | Given previously computed site-dependent amp & phase values for the 11 | | main tides (in BLQ format), the hardisp.f routine, written by Duncan Agnew| | (UCSD), determines local dU, dS, dW displacements. The code can be found | | at the IERS Conventions Update site at | | ftp://tai.bipm.org/iers/convupdt/chapter7/hardisp.f | | This routine considers a total of 141 constituent tides using a spline | | interpolation of the tidal admittances, achieving a precision is about 1%.| | [3] Center-of-mass orbit correction | | After the Analysis Centers determine the GPS orbits in an inertial frame, | | taking account of the OTL effects as described above, it is necessary as | | a final step in generating sp3 format orbit results to account for the | | crust-frame motions due to the ocean tidal mass. This can be done by | | computing the net crustal frame translations dX(t), dY(t), and dZ(t) | | according to the method given by Scherneck at | | http://www.oso.chalmers.se/~loading/cmc.html : | | | | dX(t) = SUM_i=1,11 { Xin(i) * cos(ANGLE(t,i)) - Xcr(i) * sin(ANGLE(t,i)) }| | dY(t) = SUM_i=1,11 { Yin(i) * cos(ANGLE(t,i)) - Ycr(i) * sin(ANGLE(t,i)) }| | dZ(t) = SUM_i=1,11 { Zin(i) * cos(ANGLE(t,i)) - Zcr(i) * sin(ANGLE(t,i)) }| | | | where ?in(i) are the in-phase and ?cr(i) are the cross-phase amplitudes | | for the 11 main ocean tides. ANGLE(t,i) is the angular argument returned | | by the IERS subroutine ARG(YEAR,DOY,ANGLE) for YEAR being the (current | | year - 1900) and DOY being the day of year and fraction thereof. The ARG | | routine is available at the IERS Conventions Update website: | | ftp://tai.bipm.org/iers/convupdt/chapter7/ARG.f | | Scherneck has tabulated the center of mass motion in-phase and cross-phase| | coefficients for the various ocean models at: | | http://www.oso.chalmers.se/~loading/CMC/ | | Note that on each tidal constituent record, the entries are ordered as: | | tide, model name, Zin, Zcr, Xin, Xcr, Yin, Ycr | | using the format (a,1p,t42,3(2x,2e12.4)). | | In order to correct the GPS inertial orbits (ORB_cm) to the moving | | crust-fixed frame (ORB_sp3), in addition to whatever other transformations| | are applied, the following translations should also be made: | | ORB_cm(t) + dXYZ(t) --> ORB_sp3(t) | | where dXYZ(t) is the dX(t), dY(t), dZ(t) vector computed above. Note that| | this correction is exactly analogous to the rotational corrections that | | must be applied to create sp3 orbits whenever a sub-daily EOP tidal model | | is used in the GPS data analysis. | ============================================================================= ============================================================================= | REFERENCES | |---------------------------------------------------------------------------| | Bar-Sever, Y.E., New GPS attitude model, IGS Mail #591, 1995, | | http://igscb.jpl.nasa.gov/mail/igsmail/1994/msg00166.html | | | | Bierman, G.J. (1977). "Factorization methods for discrete sequential | | estimation, Academic Press, San Diego, Calif. | | | | 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. | | | | Bos, M.S., & H.-G. Scherneck, website at www.oso.chalmers.se/~loading/ | | | | IERS Conventions 2003, D.D. McCarthy & G. Petit (editors), IERS Technical | | Note 32, Frankfurt am Main: Verlag des Bundesamts fuer Kartographie und | | Geodaesie, 2004. | | | | Kouba, J., Improved relativistic transformations in GPS, GPS Solutions, | | 8(3), 170-180, 2004. | | | | Kouba,J., P. Tetreault, R. Ferland and F. Lahaye (1993)."IGS data | | processing at the EMR Master Control System Centre", Proceedings of | | the 1993 IGS Workshop, held at Univ. of Berne, Switzerland, March 1993, | | pp.123-132. | | | | Sovers and Border (1990). Observation model and parameter partials for the| | JPL geodetic modeling software "GPSOMC". JPL Publication 87-21, Rev. 2, | | JPL, Pasadena, CA, USA. | | | | | | 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. | =============================================================================