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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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)
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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
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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
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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