Introduction to GAMIT/GLOBK Structure of GAMIT/GLOBK. Lecture 1. Overview of course of structure

Transcription

1 Introduction to GAMIT/GLOBK Structure of GAMIT/GLOBK Lecture 1 1 Overview of course of structure o Three lecture periods per day with one afternoon tutorial session o Night-time runs to generate processed results for classes o First 2-days GAMIT o Second 2-days GLOBK o Last day utilities 2

2 Lecture 1 overview o Basics of GAMIT o Basics of GLOBK o Installation and setup 3 Basic framework: GAMIT o GAMIT: Series of programs that process GPS phase data o Parameters estimated: l l l l l Station positions Satellite orbits parameters n Initial conditions n Radiation parameters n Phase center offsets Earth orientation parameters (EOP) Atmospheric delay parameters n Time dependent Zenith delays and gradients Carrier phase ambiguities 4

3 Basic framework: GLOBK o GLOBK: Uses parameter estimates and full covariance matrices from different sources to combine results o Inputs from GPS, SLR, VLBI and SINEX files o Used to estimate quantities such as: l Site velocities from series of measurements l Satellite orbit improvement l EOP parameters l Other derived parameters 5 GAMIT Structure o History o Data types o Steps needed in processing o Files needed for processing 6

4 GAMIT History o Development started in late 1970s when MIT was building GPS receivers o Code derived from Planetary ephemeris and VLBI software o Ported to Unix in 1987 o Start of IGS in 1992 prompted development of automatic processing schemes o Fully automatic processing mid-1990s including continuous stations and campaign GPS measurements 7 Current GAMIT Status o Automation features: l FTP'ing of data and other files l Extraction of information from RINEX files l Automatic directory creation l Status/Warning files generated to monitor process o Largest automatic run: Southern California Earthquake Center Campaign Data set from

5 Data Types o L1 and L2 phase used for parameter estimation o P1 and P2 range measurements: l Cleaning data l Receiver clock error estimates (tolerance 1 microsecond=300m) o L1 and L2 combined to form ionospheric-free observable LC o Ionospheric delay called LG o Melbourne-Wellenhof Widelane WL 9 Processing steps - Major o GPS satellite orbit integration (arc) o Modeling phase and partial derivative generation (model) o GPS data cleaning and cycle slip repair (autcln) o Least-squares estimator (solve) 10

6 Processing steps - Minor o Yaw table generation for GPS satellites o Ocean tide loading coefficient generation l Explicit site values l Interpolation of gridded values o Estimation of satellite and ground receiver clock models o Display of phase residuals 11 Files needed for processing o Initial orbit information: Sources l Broadcast ephemeris from receivers l SP3 orbit files from IGS l GAMIT g-files o Earth Orientation Parameters (EOP) files: Orbit integration in inertial space o Satellite clock files (j-files) o Ocean tide files 12

7 Files continued o Moon and Sun ephemerides l orbit integration l solid Earth tides o leap-second file (UTC versus AT) o Satellite information files o GPS antenna information (phase center) o Information about stations (coordinates, receiver/antenna types and heights) o Control files for GAMIT (Lec03) 13 Data Files o Raw receiver files: UNAVCO teqc program used to convert to RINEX files o RINEX files: GAMIT converts to own format x-files o Data files can be local or ftp'd from international archives 14

8 GAMIT File summary o GAMIT uses many files: Many of these files are standard and automatically created o Automatic processing scripts either link or ftp these files. o Some files should be updated from MIT ftp site (bowie.mit.edu) o The satellite information files needs to be updated when new satellites are launched 15 GAMIT documentation o GAMIT documentation available as PDF, Postscript and RTF files l Each chapter as separate document n Chapter 1: Overview n Chapter 2: Theory n Chapter 3: File structure and names n Chapter 4: Creating input files n Chapter 5: Batch Processing n Chapter 6: Data Editing n Chapter 7: Running modules 16

9 Chapters continued l Chapter 8: Atmospheric delay models l Chapter 9: Utility programs l Chapter 10: Automatic Batch Processing o Appendices o Shell scripts include on-line documentation 17 GLOBK Structure o History o Steps in processing o Files in processing 18

10 GLOBK History o Written in mid-1980s to handle combination of VLBI data o 1989 extended to handle GPS results: GAMIT modified to output needed files o 1990's: Extensions to handle SLR data and SINEX files o Suite of programs 19 GLOBK Steps in processing o Command file driven (flexible format) o Pseudo-data files called binary h-files l Generated from GAMIT h-files (ASCII), SINEX, other formats (htoglb) o GLOBK (combination) or GLRED (smaller sessions) o Analysis 20

11 Files in processing o Very flexible: binary h-files and command files only required files o Other files can be included l Orbit files (svs format) l EOP (pmu files) l Earthquake/rename definitions l "Source" files with subsets of commands l apriori coordinate and motion files o Information not user specified files is generated by various techniques 21 GLOBK documentation o PDF, PS and RTF files with documentation o Nearly all globk suite has on-line documentation (more up to date) o Help printed when program name typed. 22

12 GAMIT/GLOBK differences o GAMIT operations and files are rigid; GLOBK uses flexible formats and is used in many different ways o 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 o Pros/Cons: GAMIT stops can be frustrating; GLOBK may appear to work but might generate erroroneous results. 23 Differences continued: o Basic aim of GAMIT is to generate positions/orbits for one day of data. Basic aim of GAMIT is to produced minimum constrained results o GLOBK used in many ways with derived parameters from basic position results; combination of results from different systems (SLR, VLBI, DORIS); generalized coordinate system definition 24

13 Getting GAMIT/GLOBK o New users (research/non-commercial license is free. Source code and executables for HP, Solaris and Linux) o Point browser to: l l Select icon to download software l Complete the license information l password is changed with every release of gamit. Once you are registered, s are sent with when new passwords are set 25 Getting GAMIT/GLOBK o Once password is given, you will be in the pub/gps/updates/source/ directory where source code and other files are kept. o You can go up a directory, to get documentation and executables o All tar files and install_software should be ftp'd to your system l etopo5 and maps not strictly needed l scherneck ocean grid file needed for ocean loading corrections. 26

14 Getting GAMIT/GLOBK o Release_notes should also be ftp'd since these contain important information about changes to software. o If you already have sofware, incremental_updates are latest changes since release. install_updates used to install new updates o In directory where tar files were ftp'd: simply type install_software. 27 Finishing install o Once installed: l make link in home directory call gg (for gamit/globk). Link points to directory where install was done. l add ~/gg/com, ~/gg/gamit/bin, ~/gg/kf/bin to path in.cshrc file l Add: setenv HELP_DIR ~/gg/help setenv INSTITUTE <3-char code> to.cshrc file o We run GAMIT/GLOBK in csh or tcsh 28

15 Summary of Structures o GAMIT: Phase data processing l Suite of programs needed for processing l Files needed from various sources l With sh_gamit: Files automatically generated l GLOBK: Combination program l Suite of programs also l Files from GAMIT and other sources o Contact GAMIT: rwk@chandler.mit.edu o Remaining lectures discuss topics in more detail 29