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User Controllable Options in GAMIT

User Controllable Options in GAMIT. Station/session information Models for orbits and station motion Models for signal propagation Controls for cycle-slip repair Sampling and estimation controls A priori values for coordinates and orbits. Primary User files. station.info

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User Controllable Options in GAMIT

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  1. User Controllable Options in GAMIT • Station/session information • Models for orbits and station motion • Models for signal propagation • Controls for cycle-slip repair • Sampling and estimation controls • A priori values for coordinates and orbits GAMIT/GLOBK Tutorial 3

  2. Primary User files • station.info • receiver type, antenna type and height as f(t) • guess.rcvant • Converts RINEX header to GAMIT standard • L-file • Prior estimates of station coordinates • sestbl. • Controls modeling and estimation for session • sittbl. • Site specific controls GAMIT/GLOBK Tutorial 3

  3. station.info • Fixed format file with station information • *TRCK SITE Station Name Ant Ht Ant N Ant E \ • 7ODM 7ODM Seven Oaks Dam 0.0083 0.0000 0.0000 \ • Rcvr AntCod HtCod Vers \ • ASHZ12 ATDMRB DHPAB 9.10 \ • Year Doy SN Start Stop • 2000 110 0 00 00 00 24 00 00 • (\ = line break for this display) • This file must be sorted by TRCK, then epoch GAMIT/GLOBK Tutorial 3

  4. TRCK SITE station_name • TRCK and SITE • 4-character code • match the 4-char code in RINEX file name • TRCK = SITE for static analysis • Change for kinematic analysis • File must be sorted by this field, then epoch • station_name • is a long (12-char) description GAMIT/GLOBK Tutorial 3

  5. AntHt, N and E, HtCod • AntHt • Raw antenna height as measured • Critical measurement! • HtCod • Defines geometry of AntHt measurement • DHPAB is RINEX standard is vertical height to antenna reference point (ARP) • N and E offsets • e.g., uncalibrated tribrach • rarely used • occupied point w.r.t. benchmark GAMIT/GLOBK Tutorial 3

  6. RCVR Vers • RCVR • 6-character codes for the receiver type • not critical except for some old receivers • or "buggy" firmware versions • Vers • version number of firmware in the receiver • Should be correct to handle SNR coding properly GAMIT/GLOBK Tutorial 3

  7. AntCode • AntCod and HtCod are critical • Sets phase center model • conversion of antenna height measurement • SLBGP -- Slant bottom ground plane GAMIT/GLOBK Tutorial 3

  8. Epoch • year and doy specify year and day of year when the values apply • times set part of day • (if it changes during UTC day) • This representation will be augmented in future version of GAMIT GAMIT/GLOBK Tutorial 3

  9. gg/tables/rcvant.dat • File contains all receivers and antennas known to GAMIT • Translates user-specified 6-character code to IGS SINEX standard. • The file in templates directory provides mapping from RINEX header information to 6-char codes. • Example lines • rcv ASHTECH^Z-XII ASHZ12 • rcv Z-XII3 ASHZ12 • swv 5F 1.00 GAMIT/GLOBK Tutorial 3

  10. gg/templates/guess_rcvant.dat • Explanation given at top of file • ^ used a represent space • Sometimes need to be careful that pattern correctly gets correct type. Should not be a problem for IGS rinex files • default lines allowed, but be careful GAMIT/GLOBK Tutorial 3

  11. Updating station.info • RINEX headers will be used to update station.info unless: • An entry already exists for the day being processed • stinf_unique is set to -u in process.defaults and entry has not changed • xstinfo set for a site in sites.defaults • An error here can be fatal • If systematic patterns appear in sky map residual plots, antenna type may be wrong GAMIT/GLOBK Tutorial 3

  12. Apriori coordinates • L-file • Geocentric latitude, longitude and radius • (Spherical, not ellipsoidal) • Coordinates (no velocities) for a single epoch • Read by model and solve • sh_gamit calls gapr_to_l • Creates an L-file from (time-dependent) coordinates and velocities from globk apr file GAMIT/GLOBK Tutorial 3

  13. Apriori coordinates (2) • sh_gamit merges entries from existing lfile for sites not in apriori file • If script still can’t find coordinates: • Uses pseudorange data in rinex file to generate point position or differential range position relative to site in sites.defaults • Use Rinex header coordinates (can block this by setting use_rxc N in process.defaults) • During the sh_gamit run, the coordinates are updated if they are in error by > 30 cm GAMIT/GLOBK Tutorial 3

  14. sh_gamit runs autcln • a priori coordinates need to be < 10 m • with default settings • autcln can be "de-tuned" to allow worse • Post-2000, No SA: • receiver-estimated coordinates fine • Pre-2000 with SA: • differential range position needed • Common problem with campaign data GAMIT/GLOBK Tutorial 3

  15. sestbl. controls • file resides in tables directory • important options: • parameters for running model • estimation procedures for solve • some site-specific info also in sittbl. • if conflict, sittbl. takes precedence (automatic) GAMIT/GLOBK Tutorial 3

  16. Primary sestbl. entries • Satellite constraints • defaults for post-IGS (1992) regional data • for broadcast ephemeris • used, increase 6 Keplerian elements to 1 ppm • increase radiation parameters to 100 (%) • Type of Analysis 0-ITER (keep) • Assumes a-priori coordinates are good GAMIT/GLOBK Tutorial 3

  17. sestbl. observables • LC_HELP • uses pseudoranges to help fix ambiguities. • works well for regional networks • LC_only • uses phase data only to fix ambiguities • quicker, works well for global networks GAMIT/GLOBK Tutorial 3

  18. sestbl. observables (continued) • L1, L1+L2 • Single frequency phase combinations • best for short baselines (e.g., ties) • ionospheric effects are 1-10 ppm • therefore 1-10 mm per km of site separation • But use caution with mixed antenna types GAMIT/GLOBK Tutorial 3

  19. Decimation • Speeds up processing • factor 4 usual for 30-second data • Our practice is to • use short term position scatter with sigma at this decimation and data noise sigmas • This has little effect on positions for sampling up to 5 minutes • Uncertainty (sigma) • goes as square root of number of data GAMIT/GLOBK Tutorial 3

  20. autcln control options • Command file name autcln.cmd keep • AUTCLN Postfit: • Y runs prefit run to get data noise model • R iterates if pre-fit RMS is too high • Use N-file: • Y autcln computes an elevation angle dependent noise estimates for each site, assuming • data variance = A2 + (B/sin(elev))2 GAMIT/GLOBK Tutorial 3

  21. autcln control options (continued) • Delete AUTCLN input C-files • Controls speed and size of run • YES -- deletes all cfiles during run. Re-runs model between cleaning and estimation. Needed if bad apriori coordinates. Uses least disk space • Intermediate -- Deletes intermediate C-file, similar to yes • NO -- Keeps C-files and uses more disk space, but faster. Good for continuous array processing. GAMIT/GLOBK Tutorial 3

  22. Atmospheric delay estimation • Zenith delays and gradients • Number of points in piecewise continuous function • Overall constraint • First order Gauss Markov parameters (variance and correlation time) • Number of gradient parameters • overall constraint GAMIT/GLOBK Tutorial 3

  23. Atmospheric delays • Defaults are good for most conditions • If turbulent conditions, then constraints should be loosened (increased numerical values) • Elevation cutoff angle (with N-file not so critical) • Autcln should be consistent (cleaning minimum elevation < estimation minimum elevation) GAMIT/GLOBK Tutorial 3

  24. model parameters • Antenna Model • ELEV is most common • Important when mixing antenna types • Tide Model (1 bit for each option) • 1 -- Earth tide • 2 -- Frequency dependent K1 • 4 -- Pole tide (IGS/ITRF standard) • Can also be applied in GLOBK • 8 -- Ocean loading (need ocean grid file) • Binary sum defines the model, e.g., 1+5=6 GAMIT/GLOBK Tutorial 3

  25. model options: EOP, Yaw • EOP model choices • Diurnal and semidiurnal modes • 1 -- Pole • 2 -- UT1 • 4 -- Use Ray model (VLBI model if bit2=0) • YAW model • to handle satellite rotation • default is Y • some problems with old data during and after eclipses GAMIT/GLOBK Tutorial 3

  26. solve options • Controls how solve performs the least squares estimation • Estimate_EOP • binary coded • can be constrained later in globk run • UT1 and wobble constraints. • usually done later in GLOBK • but can be tightened in solve for regional analysis GAMIT/GLOBK Tutorial 3

  27. Cleaning options • Quick-pre • sets estimation type for the prefit run • can be made fast with decimation and observable • Delete eclipse data • POST -- 30 minutes after eclipse • ALL -- POST but data in eclipse • Mainly an issue for global data sets GAMIT/GLOBK Tutorial 3

  28. Ambiquity resolution • Defaults optimized for regional networks (<1000 km). Default is 500. • Wide lane (L1-L2) and narrow lane (L1) • Ionospheric constraint plus range data • default values work well (see Section 5.5) • Constraints on good apriori coordinates help GAMIT/GLOBK Tutorial 3

  29. sittbl. site-dependent options • Normally not changed • Mainly constraints on apriori apriori station coordinates • Distribution example has IGS sites plus others • Takes precedence over sestbl. • Not all columns are required GAMIT/GLOBK Tutorial 3

  30. Summary • User-controllable files add flexibility • Modifications seldom required • Distribution example is for regional net • Some changes appropriate for • global data processing • operation near real-time GAMIT/GLOBK Tutorial 3

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