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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 29-Dec-18 GAMIT/GLOBK Tutorial 3

2 Primary User files station.info guess.rcvant L-file sestbl. sittbl.
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 29-Dec-18 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 \ Rcvr AntCod HtCod Vers \ ASHZ12 ATDMRB DHPAB \ Year Doy SN Start Stop (\ = line break for this display) This file must be sorted by TRCK, then epoch 29-Dec-18 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 29-Dec-18 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 29-Dec-18 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 29-Dec-18 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 29-Dec-18 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 29-Dec-18 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 29-Dec-18 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 29-Dec-18 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 29-Dec-18 GAMIT/GLOBK Tutorial 3

12 Apriori coordinates L-file sh_gamit calls gapr_to_l
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 29-Dec-18 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 29-Dec-18 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 29-Dec-18 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) 29-Dec-18 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 29-Dec-18 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 29-Dec-18 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 29-Dec-18 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 29-Dec-18 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 29-Dec-18 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. 29-Dec-18 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 29-Dec-18 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) 29-Dec-18 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 29-Dec-18 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 29-Dec-18 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 29-Dec-18 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 minutes after eclipse ALL -- POST but data in eclipse Mainly an issue for global data sets 29-Dec-18 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 29-Dec-18 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 29-Dec-18 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 29-Dec-18 GAMIT/GLOBK Tutorial 3


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