From jimr at ngs.noaa.gov Wed Apr 26 10:29:32 2006 From: jimr at ngs.noaa.gov (Jim Ray (NGS 301-713-2850 x112)) Date: Wed, 26 Apr 2006 13:29:32 -0400 (EDT) Subject: [IGSMAIL-5345]: draft analysis summary Message-ID: <200604261729.NAA21273@ness.ngs.noaa.gov> ****************************************************************************** IGS Electronic Mail 26 Apr 10:30:15 PDT 2006 Message Number 5345 ****************************************************************************** Author: Jim Ray Below is a draft update of the IGS Analysis Strategy Summary. This version has many changes compared to the prior versions used by the IGS, including a number of pending/planned changes to the IERS Conventions. It is a template of specific responses that should be modified according to the procedures actually used by any given group. Numerous notes and explanatory comments are included. The summary will be considered at the IGS Workshop on 08 May. Since it is intended to be understood by users of IGS products, not just Analysis Centers are invited to review and make comments. Thanks for your consideration. ============================================================================= | IGS ANALYSIS STRATEGY SUMMARY | ============================================================================= | Analysis Center | [center name] | | | [ACN = Analysis Center code] | | | [address] | | | [group phone number] | | | [group fax number] | |---------------------------------------------------------------------------| | Contact people | [name 1] [e-mail 1] [phone 1] | | | [name 2] [e-mail 2] [phone 2] | | | [name 3] [e-mail 3] [phone 3] | |---------------------------------------------------------------------------| | Software used | [name/version], [developer], [YYYY-MM-DD implemented] | |---------------------------------------------------------------------------| | IGS products | ACNwwwwn.sp3 daily orbit files | | generated for | ACNwwww7.erp weekly ERP file of daily values | | GPS Week 'wwww' | ACNwwwwn.clk daily station & SV clock files | | day of Week 'n' | ACNwwww7.sum weekly summary file | | (n=0,1,...,6) | ACNwwww7.snx weekly SINEX file | | | ACNwwwwn.tro daily tropo files (???) | | | ACNGDDD0.YYI daily ionosphere maps (???) | | | | | | [ACN = Analysis Center code] | | | [wwww = GPS week number] | | | [n = GPS day of week number] | | | [DDD = day of year] | | | [YY = year of century] | |---------------------------------------------------------------------------| | Preparation date | YYYY-MM-DD | |---------------------------------------------------------------------------| | Modification dates| YYYY-MM-DD: ... [items changed & summary] | | | YYYY-MM-DD: ... [items changed & summary] | |---------------------------------------------------------------------------| | Effective date | YYYY-MM-DD | | for data analysis | | ============================================================================= ============================================================================= | MEASUREMENT MODELS | |---------------------------------------------------------------------------| | Preprocessing | RINEX files pre-screened using TEQC metrics to reject | | | small/incomplete files (<85%), excessive phase slips | | | (>500), or high multipath (>1.2 m); | | | outliers edited & cycle slips detected/fixed; | | | 1 ms RINEX clock jumps fixed using clockprep; | | | code biases corrected to P1/P2 using cc2noncc; | | | | | | [examples shown here; summarize any such preprocessing | | | steps] | |---------------------------------------------------------------------------| | Basic observable | undifferenced carrier phases & pseudoranges | | | [or carrier phase only for double-differencing] | | |--------------------------------------------------------| | | elevation angle cutoff: 10 degrees | | | sampling rate: 5 minute (decimated) | | | weighting: (for raw obs *before* iono correction) | | | carrier phase= 1 cm sigma (nominally) | | | pseudorange= 1 m sigma (nominally) | | | sigmas increase with decreasing elevation | | | angle by factor (1/sin(elev)) | | | deweighting: ... [summarize algorithm, if any] | | | smoothing: ... [summarize procedure, if any] | | | code biases: C1 & P2' corrected to P1 & P2 using | | | cc2noncc tool depending on receiver type | |---------------------------------------------------------------------------| | Modeled | undifferenced, corrected for 1st order ionosphere | | observable | effect to LC & PC | |---------------------------------------------------------------------------| |*Satellite center | SV-specific z-offsets & block-specific x- & y-offsets | | of mass | (from manufacturer) from file igs05_wwww.atx based on | | offsets | GFZ/TUM analyses using fixed ITRF2000 coordinates | | | [refer to IGS Mail #5189, 17 Aug 2005] | |---------------------------------------------------------------------------| |*Satellite phase | block-specific nadir angle-dependent "absolute" PCVs | | 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 igs_05.atx; | | calibration | otherwise radome effect neglected | |---------------------------------------------------------------------------| |*Marker -> antenna| dN,dE,dU eccentricities from site logs applied to | | ARP eccentricity | compute station coordinates | |---------------------------------------------------------------------------| | Troposphere | met data input: latitude, height, DOY climate model | | a priori model | from T. Herring (private comm.); | | | rel. humidity set to 50% for all sites | | (parameter |--------------------------------------------------------| | estimation is | zenith delay: Saastamoinen (1972) "dry" + "wet" | | below) |--------------------------------------------------------| | | mapping function: NMF for dry & wet parts (Niell, 1995)| | |--------------------------------------------------------| | | gradient model: ... | | | [NOTE: hydrostatic troposphere has equatorial bulge] | |---------------------------------------------------------------------------| |*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 (dehanttideinel.f routine) | | 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: not applied (no model available yet)| | | [IERS model under development] | | |--------------------------------------------------------| | |*ocean tide loading: consistent with IERS 2003 (Ch. 7), | | | site-dependent amps & phases from Bos | | | & Scherneck website for FES2004 tide | | | model; NEU site displacements computed | | | using hardisp.f from D. Agnew | | | | | | [NOTE: IERS model is not well specified] | | |--------------------------------------------------------| | |*ocean tide geocenter: coeffs corrected for center of | | | mass motion of whole Earth | | | | | | [NOTE: IERS Conventions are ambiguous; geocenter motion| | | should also be included in translation of sp3 orbits | | | from inertial to terrestrial frame using whole-Earth | | | coefficients for each tide model given at Bos-Scherneck| | | website.] | | |--------------------------------------------------------| | | 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 (ortho_eop.f)| | |--------------------------------------------------------| | (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: prograde diurnal polar motion | | should not be | corrections (IERS 2003, Table 5.1) applied | | applied) | using IERS routine PMsdnut.for | | |--------------------------------------------------------| | | | [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 | | | (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 | use all available stations of the 99 IGb00 set, plus | | network | add others based mostly on geometry up to a total of | | | 150 stations; data are processed in double-difference | | | subnets and combined at the normal equation level; | | | a core net ensures interconnection of the subnets | |---------------------------------------------------------------------------| | Interconnection | precession: IAU 1976 Precession Theory | | |--------------------------------------------------------| | (EOP parameter | nutation: IAU 1980 Nutation Theory, with daily offset | | estimation is | corrections applied from IERS Bulletin A | | below) | | | | [NOTE: errors in 1980 model are sufficiently | | | large that observational corrections should | | | be applied; even with more recent nutation | | | models observational corrections are still | | | needed to account for time-varying FCN | | | effects, which are not predictable] | | |--------------------------------------------------------| | | 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 = 6378136.6 m | |---------------------------------------------------------------------------| | Tidal variations |*solid Earth tides: procedure given in IERS Conventions | | in geopotential | 2003, Chapter 6.1, including anelastic effects and | | | step 2 frequency-dependent corrections to Love | | | number k(2,1) | | |--------------------------------------------------------| | | ocean tides: procedure given in IERS Conventions 2003, | | | Chapter 6.4 applied | | |--------------------------------------------------------| | |*solid Earth pole tide: IERS 2003, Chapter 6.2 | | |--------------------------------------------------------| | | oceanic pole tide: new model of S. Desai applied for | | | C21 and S21 terms only | | | [see IERS Conventions updates] | |---------------------------------------------------------------------------| | Third-body | Sun, Moon, Mercury, Venus, Mars, Jupiter, Saturn | | forces | (regarded as point masses) | | |--------------------------------------------------------| | | ephemeris: JPL DE405 | | |--------------------------------------------------------| | | GM_Sun 132712442076.0000 km**3/sec**2 | | | Moon-Earth mass ratio 0.0123000383 | | | 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 | |---------------------------------------------------------------------------| | Solar radiation | a priori: GSPM_EPS model of Bar-Sever (private comm.) | | pressure model | parameterized for variations in direct & | | | orthogonal forces | | (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 | |---------------------------------------------------------------------------| |*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 | variable (high) order Adams predictor-corrector | | integration | with direct integration of second-order equations | | |--------------------------------------------------------| | | integration step: variable | | |--------------------------------------------------------| | | starter procedure: RKF | | |--------------------------------------------------------| | | arc length: 3+24 hours | ============================================================================= ============================================================================= | ESTIMATED PARAMETERS (& APRIORI VALUES & CONSTRAINTS) | |---------------------------------------------------------------------------| | Adjustment | weighted least squares implemented as a Kalman filter | | method | | | | [or weighted least squares and Helmert blocking used | | | to process subnetworks separately and then combine] | |---------------------------------------------------------------------------| |*Station | all station coordinates are adjusted, relative to the | | coordinates | a priori values from IGS03P33_RS106.snx; a no-net- | | | rotation condition is applied wrt the IGb00 frame | | | using up to 99 reference frame stations; | | | apriori sigmas are 1 m for each component | |---------------------------------------------------------------------------| | Satellite clock | solved for at each epoch as white noise process with a | | | a steady state sigma of 1 sec | | |--------------------------------------------------------| | | sp3,clk files: frame for clocks corresponds to ITRF | | | origin by constraining station positions| | | and back-solving for clocks | | | [or clocks consistent with apparent center-of-mass | | | frame and determined simultaneously with station | | | positions; this is not recommended for IGS products] | |---------------------------------------------------------------------------| | Receiver clock | solved for at each epoch as white noise process with a | | | a steady state sigma of 1 sec; one station clock fixed | | | & used as a timescale reference, usually USNO | |---------------------------------------------------------------------------| | Orbits | deterministic positions and velocities, y-bias, solar | | | radiation pressure scale in direct direction; | | | stochastic accelerations in SV x,y,z directions with | | | steady state sigma of 0.125e-12 km/s/s and correlation | | | time of 4 hrs solved for every 30 min, nominally; | | | stochastic sigma increased for SV with poor fits based | | | on prior preliminary solution or prior history; | | | apriori values are based on solution for previous day | | | [or whatever procedures are actually used ...] | | |--------------------------------------------------------| | | 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 as a | | | random walk with process noise of | | | 1.0 cm/sqrt(hr) | | | [or if segmented model used give model | | | form and segment interval] | | |--------------------------------------------------------| | | mapping function: partial is NMF wet (Niell, 1995) | | |--------------------------------------------------------| | | zenith delay epochs: reported for each observation | | | epoch | | | [if segmented model used, give epochs of | | | tabulated values] | | |--------------------------------------------------------| | | gradients: one N-S and one E-W gradient parameter per | | | day for each station, constrained to | | | 10 mm at 10 deg elevation angle | |---------------------------------------------------------------------------| | Ionospheric | not estimated | | correction | | |---------------------------------------------------------------------------| | Ambiguity | phase cycle ambiguities adjusted except when double- | | | ambiguities can be resolved confidently (<2 cm | | | uncertainty), in which case they are fixed; fixing is | | | successful for 98% of obs on all baselines <2000 km | |---------------------------------------------------------------------------| |*Earth orientation| daily x & y pole offsets, pole-rates, and LOD at noon | | parameters (EOP) | epochs; rates constrained to 32.2 mas/day; | | | UT1 not estimated | |---------------------------------------------------------------------------| | Other | ... [explain] | | parameters | | ============================================================================= ============================================================================= | REFERENCES | |---------------------------------------------------------------------------| | | | Bar-Sever, New GPS attitude model, IGS Mail #591, 1995, | | http://igscb.jpl.nasa.gov/mail/igsmail/1994/msg00166.html | | | | 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. | | | | Niell, A.E., Global mapping functions for the atmosphere delay at radio | | wavelengths, J. Geophys. Res., 101(B2), 3227-3246, 1993. | | | | 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. | | | | 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 | =============================================================================