Transcript PowerPoint Presentation - 12.215 Modern Navigation

Introduction to GAMIT/GLOBK
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
18-Jul-15
GAMIT/GLOBK Tutorial 1
2
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
18-Jul-15
GAMIT/GLOBK Tutorial 1
3
GAMIT Structure
•
•
•
•
History
Data types
Steps needed in processing
Files needed for processing
18-Jul-15
GAMIT/GLOBK Tutorial 1
4
GAMIT History
• Development started in late 1970s when MIT was
building GPS receivers
• Code derived from 1960-1970 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
18-Jul-15
GAMIT/GLOBK Tutorial 1
5
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 campaignstyle data set from 1992-2002
18-Jul-15
GAMIT/GLOBK Tutorial 1
6
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
18-Jul-15
GAMIT/GLOBK Tutorial 1
7
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)
18-Jul-15
GAMIT/GLOBK Tutorial 1
8
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
18-Jul-15
GAMIT/GLOBK Tutorial 1
9
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
18-Jul-15
GAMIT/GLOBK Tutorial 1
10
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
18-Jul-15
GAMIT/GLOBK Tutorial 1
11
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
18-Jul-15
GAMIT/GLOBK Tutorial 1
12
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
18-Jul-15
GAMIT/GLOBK Tutorial 1
13
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
18-Jul-15
GAMIT/GLOBK Tutorial 1
14
GAMIT documentation
• GAMIT documentation available as PDF, Postscript
and RTF files
– Each chapter as separate document
•
•
•
•
•
•
•
18-Jul-15
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
GAMIT/GLOBK Tutorial 1
15
Chapters continued
– Chapter 8: Atmospheric delay models
– Chapter 9: Utility programs
– Chapter 10: Automatic Batch Processing
• Appendices
• Shell scripts document themselves
18-Jul-15
GAMIT/GLOBK Tutorial 1
16
GLOBK Structure
• History
• Steps in processing
• Files in processing
18-Jul-15
GAMIT/GLOBK Tutorial 1
17
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
18-Jul-15
GAMIT/GLOBK Tutorial 1
18
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
18-Jul-15
GAMIT/GLOBK Tutorial 1
19
Required files
• binary h-files generated by htoglb from:
– GAMIT h-files (ASCII),
– SINEX
– other
• command files
– very flexible, key-word structure
18-Jul-15
GAMIT/GLOBK Tutorial 1
20
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
18-Jul-15
GAMIT/GLOBK Tutorial 1
21
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.
18-Jul-15
GAMIT/GLOBK Tutorial 1
22
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.
18-Jul-15
GAMIT/GLOBK Tutorial 1
23
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)
18-Jul-15
GAMIT/GLOBK Tutorial 1
24
Getting GAMIT/GLOBK
• Free for research/non-commercial license
• Fortran Source code
• Executables for HP, Solaris and Linux
18-Jul-15
GAMIT/GLOBK Tutorial 1
25
Getting GAMIT/GLOBK (2)
• Point browser to
– http://www-gpsg.mit.edu/~simon/gtgk/index.html
• Click on
icon to download software
• Complete the license information, and send via e-mail
to [email protected]
• Password changes with every new release.
– Registered users will receive an email message
when new passwords are set
18-Jul-15
GAMIT/GLOBK Tutorial 1
26
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.
18-Jul-15
GAMIT/GLOBK Tutorial 1
27
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
18-Jul-15
GAMIT/GLOBK Tutorial 1
28
Installing GAMIT/GLOBK
• In the directory on your machine containing the tar
files, simply type install_software
• Wait a while.
18-Jul-15
GAMIT/GLOBK Tutorial 1
29
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
18-Jul-15
GAMIT/GLOBK Tutorial 1
30
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:
[email protected]
18-Jul-15
GAMIT/GLOBK Tutorial 1
31