1. Introduction to GAMIT/GLOBK

2. Basic framework: GAMIT
GAMIT: Series of programs that analyze GPS phase data to estimate parameters:
Station positions (coordinates)
assumed constant at epoch of data
Satellite orbital parameters
Initial conditions
Radiation parameters
Phase center offsets
Earth orientation parameters (EOP)
Atmospheric delay parameters
Time-dependent Zenith delays and gradients
Carrier phase ambiguities
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3. Basic framework: GLOBK
GLOBK combines solutions from GPS, SLR, & VLBI data via their parameter estimates and full covariance matrices to estimate other parameters:
Site velocities
temporal derivative of position in mm/yr
requires a time series of measurements
Satellite orbit adjustments
EOP parameters
Others parameters, e.g., co-seismic displacements
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4. GAMIT Structure History Data types Steps needed in processing
Files needed for processing
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5. GAMIT History
Development started in late 1970s when MIT was building GPS receivers
Code derived from planetary ephemeris and VLBI software
Ported to Unix in 1987
Start of IGS in 1992 prompted development of automatic processing schemes
Fully automatic processing mid-1990s including continuous stations and campaign GPS measurements
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6. Current GAMIT Status Automatic features:
FTP'ing of data and other files
Extraction of information from RINEX files
Automatic creation of directories
Status/Warning files to monitor process
Largest automatic run:
Southern California Earthquake Center campaign-style data set from
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7. Data Types L1 and L2 phase used for parameter estimation
P1 and P2 range measurements
used to help clean phase data
used to estimate receiver clock offset with tolerance of 1 microsecond (= 300 m)
LC phase
proportional to geometric range
sensitive insensitive to ionospheric delay
linear combination of L1 and L2
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8. Data Types (cont’d) LG phase measures ionospheric delay only
insensitive to geomery
Widelane WL
linear combination of L1, L2, P1 and P2
Melbourne-Wubbena
Should be constant (+/- noise)
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9. Major steps for GAMIT arc integrates GPS satellite orbits model:
calculates theoretical (modeled) phase
partial derivatives of phase w.r.t. parameters
autcln
cleans GPS data and repairs cycle slips
solve
estimates parameters via least squares
calculates goodness of fit
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10. Minor steps for GAMIT Generate yaw table for GPS satellites
Ocean tide loading coefficients
Explicit site values
Interpolation of gridded values
Estimation clock models
satellite frequency standard
ground receiver clock
Display phase residuals
time series
sky plot
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11. Files needed for processing
Control files for GAMIT (Lecture 03)
Initial orbit information from:
Broadcast ephemeris from receivers
SP3 orbit files from IGS
GAMIT g-files
Earth Orientation Parameters (EOP) files:
arc integrates in inertial frame
Satellite clock files (J-files)
Ocean tide files
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12. Files (continued) Moon and Sun ephemerides orbit integration
solid Earth tides
leap-second file (UTC versus GPST or TAI)
Satellite information files
Information about stations
prior (approximate) estimates of coordinates
receiver and antenna types
antenna heights
models for GPS antenna phase center
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13. Data Files Raw receiver files UNAVCO teqc program translates to RINEX
RINEX files:
GAMIT converts to own format x-files
Data files:
local, or
ftp'd from international archives
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14. GAMIT File summary GAMIT uses many files
Many of these files are standard and automatically created
Automatic processing scripts either link or ftp these files.
Some files should be updated from MIT ftp site (bowie.mit.edu)
For example, the satellite information files need to be updated when new satellites are launched
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15. GAMIT documentation
GAMIT documentation available as PDF, Postscript and RTF files
Each chapter as separate document
Chapter 1: Overview
Chapter 2: Theory
Chapter 3: File structure and names
Chapter 4: Creating input files
Chapter 5: Batch Processing
Chapter 6: Data Editing
Chapter 7: Running modules
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16. Chapters continued Chapter 8: Atmospheric delay models
Chapter 9: Utility programs
Chapter 10: Automatic Batch Processing
Appendices
Shell scripts document themselves
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17. GLOBK Structure History Steps in processing Files in processing
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18. GLOBK History Suite of programs
Written in mid-1980s to handle combination of VLBI data
Extended in 1989 to handle GPS results: GAMIT modified to output needed files
1990's: Extensions to handle SLR data and SINEX files
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19. GLOBK philosophy Driven by command files
Flexible format and file-naming
Accepts solutions from upstream analysis
Input upstream solutions as binary h-files
globk (combination)
glred (smaller sessions, one at a time)
glorg (generalized constraints)
Analysis & interpretation
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20. Required files binary h-files generated by htoglb from:
GAMIT h-files (ASCII),
SINEX
other
command files
very flexible, key-word structure
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21. Optional files Orbit files (svs format) EOP (pmu files)
Earthquake/rename definitions
"Source" files with subsets of commands
apriori coordinate and motion files
Information not specified by user files is generated by various techniques
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22. GLOBK documentation Available as PDF, PS and RTF files
Nearly all modules in GLOBK suite have up-to-date documentation on-line
To get help for a command, type its name alone on the command line.
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23. Differences between GAMIT and GLOBK
GAMIT operations and files are rigid; GLOBK uses flexible formats and is used in many different ways
GAMIT tends to stop if a problem is encountered (less so these days); GLOBK tries to continue as far as it can by defaulting values
Pros/Cons: GAMIT stops can be frustrating; GLOBK may appear to work but might generate erroneous results.
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24. Differences (continued)
Basic aim of GAMIT is to generate positions/orbits for one day of data. Standard product of GAMIT is a minimally constrained solution
GLOBK flexibly combines minimally constrained parameter estimates from one or more measurement types (GPS, SLR, VLBI, DORIS)
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25. Getting GAMIT/GLOBK Free for research/non-commercial license
Fortran Source code
Executables for HP, Solaris and Linux
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26. Getting GAMIT/GLOBK (2)
Point browser to
Click on icon to download software
Complete the license information, and send via to
Password changes with every new release.
Registered users will receive an message when new passwords are set
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27. Getting GAMIT/GLOBK (3)
Enter password
Your working directory is now
pub/gps/updates/source
contains source code and other files
Copy all *.tar files and install_software to your machine
etopo5 and maps not strictly needed
Scherneck ocean grid file needed for ocean loading corrections.
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28. Getting GAMIT/GLOBK (4)
To get documentation or executables, go up one directory (cd ../)
Remember to read the file release_notes to learn about important changes to the software.
If you already have a previous release,
the incremental_updates directory contains the latest changes since the previous release.
Then use install_updates
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29. Installing GAMIT/GLOBK
In the directory on your machine containing the tar files, simply type install_software
Wait a while.
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30. After installation script finishes:
Use ln -s to make link in home directory called gg (for gamit/globk). This should link points to the same directory as install_software was done.
Add to $path in ~/.cshrc file
~/gg/com ~/gg/gamit/bin ~/gg/kf/bin
Also add to your ~/.cshrc file
setenv HELP_DIR ~/gg/help
setenv INSTITUTE <3-char code>
We use the tcsh or csh shells
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31. Summary GAMIT: Phase data processing
Suite of programs needed for processing
Files needed from various sources
Automatic script sh_gamit generates most files
GLOBK: Combination program
Also a suite of programs
Files from GAMIT and other sources
Contact person for GAMIT/GLOBK:
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