GPS Data processing using GAMIT/GLOBK

16-19 November 2012 Kathmandu, Nepal


Instructor: Prof. Thomas Herring, MIT


This short course will focus on the tectonic applications of GPS.  It will include lectures and one-on-one tutoring for both continuous and survey mode measurements. The lectures will include a basic discussion of how to use GAMIT and GLOBK; defining, global, regional, and local reference frames; temporal and spatial filtering of time series; modeling tropospheric, antenna, and loading effects in height estimates; combining solutions to estimate post-seismic and long-term crustal deformation; handling step-displacements due to earthquakes and instrument changes; developing an error model for velocity estimates.   The tutorial sessions, held at the end of each day, will run through the example data set distributed with the software and, in later sessions, a data set that includes an earthquake. The latter data set is aimed at showing the methods used to treat earthquakes both in GAMIT and GLOBK.

Participants will be expected to have exercised the software on their own before the workshop and should bring laptops with the software installed or with remote access to their own labs.


Students un-familiar with UNIX can look at the material in the last lecture that discusses some basic commands and features of UNIX.  Students should go through this material before the workshop.  Specifically, .cshrc or .bashrc files (depending which shell is used) should be modified for GAMIT/GLOBK processing before the workshop.


Seminar on Geodesy Imaging       Herring_KeyNote.pptx         animations.tar










Course Logistics and Introduction to GPS




GAMIT: Standard Processing




Tutorial: Standard GAMIT Example




GLOBK Overview




Modeling details




Tutorial: GLOBK processing in GAMIT Example




Reference Frame Realization




Errror analysis of GPS estimates




GAMIT processing of earthquake affected data (El Mayor Cucapah aftershock




GLOBK Prototyping tools




Utility programs and scripts




GLOBK processing of earthquake data





Notes and data sets


Fri        13:30-15:00     Course logistics Introduction to GPS                         L01

In this lecture we go through the basic layout of the short course. We also introduce some of the basic concepts in GPS data processing, which we will revisit in later lectures. We look at the basic GPS observables and examine those contributions that are most uncertain in processing data. The main conclusions from this lecture are that high precision GPS requires external information in addition to just the GPS data and orbit information. In the current processing methods, all of the external information needed by GAMIT is automatically obtained but an Internet connection is required for access to information in international data archives.

Katmandu_Lec01_Intro.pptx                       Katmandu_Lec01_Intro.pdf


           15:30-17:00      GAMIT Standard Processing                                              L02

In this lecture we look at daily processing using GAMIT. Nearly always the shell script sh_gamit is used for this processing. We will look at the directory structures that are normally used and the main functions and programs that are used in daily processing. We then look at the files that are important, and need user input, that are used in the processing. These files include station information, coordinates and velocities for stations, and other files that need to be kept up to date. We also look at the summary files that are generated and examine how to interpret these files. We also look at residual plots, which can be illustrative of problems in data processing. Finally we look at problems that can happen during processing and add some suggestions on how to solve these problems.

Katmandu_Lec02_gamit.pptx                     Katmandu_Lec02_gamit.pdf

           17:00-               Tutorial session         

This first tutorial will cover the standard gamut example that is distributed with the software. The GAMIT Part of the example will be examined in detail.


Sat      13:30-15.00      GLOBK Overview                                                               L03

in this section we review the main features of globk and glred. It is important to note that glred is a simple program that allows multiple runs of globk and is used typically for time series generation. The topics we cover are the basic flow from daily gamit processing results (hfiles) to the results generated with globk.  We briefly review Kalman filtering and we look at the globk files and the estimation rules used. The program glorg which can be either run by itself or from within globk, is used to define the origin and orientation of the reference frame for the globk results.  We examine the output options and briefly look at the sh_glred script, which is a convenient way of invoking globk and its ancillary programs.

Katmandu_Lec03_globk.pptx                     Katmandu_Lec03_globk.pdf

           15:30-17:00      Modeling details                                                                L04

In this lecture we look in more details at some aspects of modeling data in GPS processing.  We will look at effects that can be considered signal and sometimes noise in GPS processing. The basic areas we discussed our atmospheric delay modeling and signal scattering, and loading affects from the ocean, atmosphere and water.

Katmandu_Lec04_models.pptx                  Katmandu_Lec04_models.pdf  


           17:00-               Tutorial session         

This tutorial session will focus on the standard gamut example. In this case we will look at the GLOBK portion.


Sun     13:30-15:00      Reference Frame Realization                                            L05

In this lecture we introduce the concepts of reference frame realization and the methods used in globk a to generate results in a specific reference frame. As we saw in earlier lectures, sites are affected by loading, mostly in the vertical direction, and these effects influence the reference frame realization. We look at ways of handling this in globk. We also examine local reference frame realizations and the way that earthquakes need to be treated in large analyses.

Katmandu_Lec05_RefFrame.pptx              Katmandu_Lec05_RefFrame.pdf

           15:30-17.00      Statistics of time series                                                     L06

We review the sources of noise in GPS position determinations and we look at some of the methods used to characterize noise. We look at the “realistic sigma” algorithm that is implemented in globk and tsview.  We also look at some methods that can be used to judge the quality of the uncertainty estimates derived by different techniques. Finally we look at the tools that are available in gamit/globk for error analysis and assessment.

Katmandu_Lec06_ErrorMod.pptx               Katmandu_Lec06_ErrorMod.pdf


           17:00-               Tutorial session Earthquake data set

This tutorial we will do standard gamit processing using data in southern California. The stations used here are only a small set of those that are available through the Unavco archive. On day 166 of 2010 an aftershock of the El Mayor Cucapah earthquake that occurred in April of 2010, occurs. On this day we will use the sessinfo option in sh_gamit to break the day before and after the quake. Included in the same data set are hfiles from many more days of data that we will use in the globk tutorial.



Mon    13:30-15:00      Globk Prototyping tools                                                     L07

In this lecture we look at tools that can be used to test large globk solutions.  These tools allow timeseries to be analyzed for discontinuities from equipment changes and earthquakes and allow earthquake files to be developed that can be used in globk. These programs can also be used to realign reference frames very rapidly and to fit parameters for periodic signals and earthquakes. The a priori coordinate files generated here can contain the extended entries (periodic signals, earthquake the seismic signals) that can be used in globk. For large data sets these prototyping tools allow efficient testing of a globk run that might take one or two days to execute.

Katmandu_Lec07_Protoptype.pptx            Katmandu_Lec07_Protoptype.pdf


           15:30-17:00      Utility programs and scripts                                              L08

This lecture covers utility programs and scripts. These are organized into preprocessing and organization scripts, scripts that are used inside sh_gamit but are also useful standalone, and scripts that are useful for evaluating results. We also briefly review UNIX shell programs that are used extensively and are good to be familiar with.

Katmandu_Lec08_utilities.pptx                 Katmandu_Lec08_utilities.pdf


           17:00-               Final Tutorial session

We will work on the data sets from previous days depending on the interests of the group. It is expected that different students will work on different projects and during this session we will have discussions informally. If an interesting issue is encountered then we may take time to present those results to the whole group.