Common applications of GLOBK

Common applications of GLOBK
Repeatability analysis (glred) individual sessions combined files Combine sessions to get average position over experiment connects stations observed separately Combine averaged positions to estimate velocities and/or earthquake offsets and post-seismic motion 19-Nov-18 Introduction to GAMIT/GLOBK

Introduction to GAMIT/GLOBK
Kalman Filtering Estimation method in which parameters can be random processes Examples: polar motion and UT1 radiation pressure effects on satellites coordinates after EQ Nearly all parameters in GLOBK can be stochastic or deterministic Statistical character set by commands apr_XXX mar_XXX 19-Nov-18 Introduction to GAMIT/GLOBK

Stochastic processes Stochastic models in globk are random walks characterized by variance of change in process over an interval of time Variance grows linearly with time (standard deviation grows as square root of time) If process noise is zero, then classed as deterministic (identical to sequential least squares) 19-Nov-18 Introduction to GAMIT/GLOBK

GLOBK Structural Confusions
gllobk and glred are the same program with (slightly) different ways of treating the h-file list Two types of solution files: h-files for saving/external exchange (backward compatible) sol file is internal, format changes with versions glorg applies generalized constraints to sol file 19-Nov-18 Introduction to GAMIT/GLOBK

GLOBK files User supplied command files (may include ‘source’ files) gdl list of h-files binary h-files (created from SINEX or GAMIT h-) apr file(s) (optional but recommended) EOP (pmu_file, optional) eq_file (optional, but must appear at top) Generated by globk srt, com, sol , svs (must be named and come first) Output files screen, log, prt, output h-file 19-Nov-18 Introduction to GAMIT/GLOBK

Things GLOBK cannot do Remove non-linear effects GLOBK assumes a linear model Repair mistakes in original analysis cycle slips wrong antenna phase center models Resolve ambiguities (would make files too large) But GLOBK can delete stations can help avoid contaminating solution 19-Nov-18 Introduction to GAMIT/GLOBK

What can go wrong ? globk H-files not used: removed for high chi2, coordinate adjustment, or rotation High chi2 increment: inconsistent data Station “missing”: not present in h-file or renamed out (use glist) glorg Stabilization fails: too-few sites in stabilization Large uncertainties: poor stabilization Too-small uncertainties for some stabiilization sites: rotation parameters should not be estimated High chi2 in equate: inconsistent data Wrong velocity for equated sites: unmatched a priori 19-Nov-18 Introduction to GAMIT/GLOBK

Program sequence globk -- Main controlling program that calls other modules glinit -- Initialization program, reads the headers of all the binary h-files to determine their contents (allows wild cards in names etc.) glfor -- Forward kalman filter glbak -- Backards running filter and smoother, invoked with glb_bak command, used only when temporal variations in stochastic parameters are needed. glsave -- Saves combined binary h-files (may be run stand-alone) glout -- Write the output files glorg -- Apply generalized constraints, site equates (often run stand-alone) 19-Nov-18 Introduction to GAMIT/GLOBK

GLOBK file handling log, prt, org files are concatenated, so should be removed or renamed unless you want them together (e.g. glred) com, srt, sol files are overwritten; com/sol should not be renamed since original sol file name is imbedded in the com file Automatic naming is available for com, srt, sol, org, and output h-files 19-Nov-18 Introduction to GAMIT/GLOBK

Estimation commands rules
For a parameter to estimated in globk, apr_xxx command must be used where xxx is a parameter type (e.g., neu, svs, wob, ut1, atm) If a parameter is not mentioned, it does not appear in the solution, but if it appears in the h-file (I.e, estimated in GAMIT), its uncertainty is implicit in the globk solution; e.g., if orbits are estimated in GAMIT and you want them constrained in globk, use apr_svs If zero given as a priori sigma, then parameter is not estimated (effectively left unconstrained) To force a parameter to it’s a priori value, use F as the a priori sigma Parameters estimated in glorg must be kept loose in globk ; if rotation or scale is not estimated in glorg, it must be tightly constrained in globk 19-Nov-18 Introduction to GAMIT/GLOBK

EOP statistics Normally used in two forms: Global network of stations apr_wob apr_ut1 10 1 Regional network (constrained). When constrained this way system is not free to rotate (see pos_org in glorg). apr_wob apr_ut In many analyses, the global form is used even for regional networks. (Care is needed if network is not not surrounded by stations with well defined motions). 19-Nov-18 Introduction to GAMIT/GLOBK

Miscellaneous commands
max_chi <max chi**2 Increment> <max prefit difference> <max rotation> - allows automatic deleting of bad h-files and bad coordinates app_ptid allows applying the pole tide correction if not included in gamit run. (Careful with SINEX files, since these don't specify if correction has been applied) 19-Nov-18 Introduction to GAMIT/GLOBK

Miscellaneous commands
crt_opt, prt_opt, org_opt specify output options for screen, print and org files globk/glorg help gives all options, main ones are: ERAS -- erase file before writing (normally files appended) NOPR -- Do not write output BLEN -- Baseline lengths BRAT -- baseline rates when velocities estimated RNRP -- generates reports on differences in parameter estimates after renames. FIXA -- makes apriori coordinates and velocities consistent when equates are used in glorg (can sometimes fail in complicated rename scenarios--best apriori files are consistent) VSUM -- Lat/long summary of velocity (needed to plot velocities) PSUM -- Lat/long position summary GDLF --Include list of hfiles and chi**2 increments from run CMDS -- Echos globk command file into output file 19-Nov-18 Introduction to GAMIT/GLOBK

Adding noise to station coordinate estimates
To account for temporal correlations in time series we typically use random-walk (RW) process noise with the mar_neu command Units are m2/year Typical values are 2.5e-8 (0.5 mm in 1 yr) to 4e-6 (2 mm in 1yr) mar_neu all 4e-6 4e-6 4e Can also add random noise (units are m) sig_neu all sig_neu ankr sig_neu HEMED 19-Nov-18 Introduction to GAMIT/GLOBK

Site coordinate modeling
Can rename sites in globk to account for earthquakes, changes in instrumentation, or ambiguous height-of-instrument (later link velocities and/or horizontal coordinates in glorg) New feature in globk is the EXTENDED options in the apriori coordinate files which allow modeling of non-secular motions (seasonal, logarithmic, exponential). Input for these options can be obtained from the ENFIT output (no scripts yet to do this automatically) 19-Nov-18 Introduction to GAMIT/GLOBK

GLORG glorg allows coordinates systems to be defined by applying explicitly rotations and translations rather than tightly constraining some stations Allows post applications of constraints (e.g. equating velocities at near by sites) If loose constraints on site positions and velocities, apriori coordinates and velocities can be changed. It can be run as a separate program or during the globk run itself 19-Nov-18 Introduction to GAMIT/GLOBK

glorg commands imbedded in globk command file
The globk command file imbedded glorg commands are: org_cmd < glorg command file name > org_opt < options for output > org_out < output file name > If org_out is not given then the extent on the print file name is replaced with .org 19-Nov-18 Introduction to GAMIT/GLOBK

GLORG Commands apr_file – Need not be the same as for globk; needs to contain values only for sites used for stabilization and sites for which coorinates or velocities are equated pos_org, rot_org – Control what parameters are estimated in stabilization xtran ytran ztran – allows translation xrot yrot zrot – allows rotation scale – allows rescaling of system (if used, estimate scale in globk) cnd_hgtv – Control relative weights of heights (variances, nominally 10) stab_ite – # of iterations and sigma-cutoff to remove a site stab_site – List of sites to use in stabilization 19-Nov-18 Introduction to GAMIT/GLOBK

GLORG Rotation If rotation used in pos_org, EOPs must be loose in globk (apr_wob/mar_wob and apr_ut1/mar_ut1) If rotation not used then EOPs should be constrained Rotation uncertainties (when estimated) or errors (when not estimated) are proportional to the distance from the centroid of the stabilization network There can be problems with zrot terms because of differences between the node position of the satellites and UT1 tables used in globk analysis. Rotation rate: EOP tables are in the no-net-rotation (NNR) frame. If analysis done in another frame (e.g., Eurasia-fixed) rotation rates should be allowed or the network kept small 19-Nov-18 Introduction to GAMIT/GLOBK

Earthquake files ( globk )
It is possible to automatically account for displacement caused by earthquakes with the earthquake file To main functions: Earthquakes specified by 2-char code renames of sites either due to wrong names in gamit processing or problem with position change after equipment change. Rename command: Rename <old> <new> [HFile code] [Epoch ranges] [Position shift] Changing positions with rename commands no longer recommended. 19-Nov-18 Introduction to GAMIT/GLOBK

Earthquakes in eq_file
For earthquake: eq_def <code> Lat Long Radius Depth Epoch eq_cosei <code> <Static Variance> <distance dependent variances> eq_post <code> <dur> <Static RW> <distance dependent RW> eq_rename <code> eq_log <code> <tau (days)> <static NEU sigma (m)> <Spatial sigma NEU> The rename option cause site to renamed from xxxx_GPS to xxxx_G[Code] 19-Nov-18 Introduction to GAMIT/GLOBK

19-Nov-18 Introduction to GAMIT/GLOBK

Associated programs Matlab derived programs (interactive): velview -- displays and analyzes velocity fields tsview -- displays and analyzse time series. Both these programs are available as executables for Linux and Mac OSX. Other program associated with globk glist -- lists the contents of a series of h-files glbtosnx -- Generates SINEX files from binary h-files hfupd -- Updates binary h-files for changes in station.info or sinex header file (distributed by IGS) glred -- Convenient way of running globk multiple times. This program is commonly used for repeatability analyses which are in turn used to set the process noise statistics in globk. ensum, enfit -- time series analysis (batch) 19-Nov-18 Introduction to GAMIT/GLOBK

UT1 issues Some care needs to be used with UT1 because it cannot be separated from the nodes of the satellites orbits UT1 tables and orbits must have used the same frame for constraints on UT1 to applied. If local processing, then should be OK If orbits were determined with different EOP tables, then UT1 should be loosened. (More of a problem with older analyses -- mid 1990’s and earlier) 19-Nov-18 Introduction to GAMIT/GLOBK

Frame estimation commands
apr_tran <X YZ> <Vx Vy Vz> -- estimate translation of coordinate system apr_scale <ppb> <ppb/yr> -- estimate scale and scale rate mar_tran and mar_scale specify the process noise Normally only used in global networks but can be help full in regional networks to allow for common mode errors. (Generally, small networks can translate easily and so explicit translation not needed). apr_scale MUST be used if scale allowed in glorg frame definition. 19-Nov-18 Introduction to GAMIT/GLOBK

File commands A number of commands are used control the files used by globk apr_file <name> lets a new apriori coordinate file be used Format is: Site_name X Y Z Vx Vy Vz epoch Site names are 8 characters, for GPS ABCD_GPS X Y Z are geocenter Cartesian (m) Velocities are m/yr Epoch is deciminal years 19-Nov-18 Introduction to GAMIT/GLOBK

Documentation GLOBK Chapter 1: Overview and list of recent changes Chapter 2: Preparing the input files Chapter 3: Running glred, globk, and glorg - command files - defining the reference frame - examples Chapter 4: GMT plotting utilities Chapter 5: Auxiliary programs - plots and statistics - file conversions - frame transformations 19-Nov-18 Introduction to GAMIT/GLOBK

Binary h-files There are number of methods and sources of binary hfiles: From Gamit, they can be generated with htoglb from the h<expt>a.<yy><doy> files in processing day directories Other major source: Solution Independent Exchange Format files (SINEX). Available for GPS, VLBI, SLR and DORIS. Older formats from VLBI, SLR and GPS can be read but now replaced by SINEX. (JPL stacov files can be read but very poor meta data in these files). Program detects which type of file is given. SINEX files should be converted one-file at a time. De-constraining options are available for SINEX and should be used. Globk itself can write binary h-files Generally: Globk assumes h-files are loosely constrained. 19-Nov-18 Introduction to GAMIT/GLOBK

HTOGLB Running htoglb Runstring: htoglb <dir> <ephemeris file> [options] <list of ascii files> dir is directory where binary files will be written ephemeris file is satellite orbit file (not used any more, make_svs). This file also contains the aproiri coordinates of the sites in the hfiles. options allow control of file names, and de-constraints: -d options allows rotation and translation covariances to be added. Needed for IGS sinex and PBO frame SINEX files. -n allows name format to be changed. list of ascii files, usually with UNIX wild cards. Single SINEX files should be used only. If no arguments are given; help is printed. 19-Nov-18 Introduction to GAMIT/GLOBK

Running globk Typing globk will list the help: Runstring: globk <crt> <print file> <log file> <gdl file> <command file> <OPT> where <crt> = 6 (screen output) <print file> -- Print file name (can be 6 for screen) <log file> -- log file name (can be 6) <gdl file> -- file containing list of hfiles to be processed. Options can be added at the ends of line to re-weight files <globk command file> -- command file name <OPT> is a string (case sensitive) such that lines which start with this string will be interpreted as commands. This allows one command files to be for different purposes such as a velocity and repeatability runs. 19-Nov-18 Introduction to GAMIT/GLOBK

globk files The gdl file is generated normally with an 'ls' of the directory containing the binary hfiles command file is created with an editor (can be based on gg/example templates version of file) print and log files are written by globk. When glorg in invoked inside globk, the .prt extent from the print file name is replaced with .org and this file is written also. Depending on options, files may not be output at all or may be erased before output (default is to append to files). 19-Nov-18 Introduction to GAMIT/GLOBK

Main globk commands Commands commonly used: Globk uses three "scratch" files which can be explicilty named com_file -- Common file contains information about run srt_file -- binary file with time-sorted list of hfiles sol_file -- binary file with solution and covariance matrix To use glorg stand-alone, com_file command must be used 19-Nov-18 Introduction to GAMIT/GLOBK

Estimation commands Site position estimation apr_neu <site> <sigN> <sigE> <sigU> <sigVN> <sigVE> <sigVU> site is site name; maybe ALL to apply to all stations. Wild at end of line can be used to apply to multiple sites (e.g., would apply to AOA1_GNR and AOA1_GHT if these both were in solution). <sigN> <sigE> <sigU> aprior sigma on position (m) <sigVN> <sigVE> <sigVU> apriori sigma on velocities (m/yr) Stochastic noise process mar_neu <site> <RWN> <RWE> <RWU> <RWVN> <RWVE> <RWVU> site name, may be all <RWN> <RWE> <RWU> Random walk positions (m2/yr) <RWVN> <RWVE> <RWVU> Random walk velocities ((m/yr)2/yr) [Normally used] 19-Nov-18 Introduction to GAMIT/GLOBK

Apriori position files
apr_files commands can be issued multiple times with the latest values taken If not specified, GAMIT apriori's are used (no velocities) EXTENDED option allows more complex behaviors (see globk.hlp) Allows for jumps in positions and velocities Periodic signals Logarithmic and exponential decay after earthquakes. 19-Nov-18 Introduction to GAMIT/GLOBK

GLORG Commands The two commands determine how coordinate system will be realized from loose globk analysis. Class of parameters: xtran ytran ztran – allows translation xrot yrot zrot – allows rotation Scale – allows rescaling of system Strictly when translation used the apr_tran and mar_tran commands should be used in globk analysis. (We are still not sure this is best thing to do.) Absolutely if scale used, apr_scale and mar_scale commands should be used in globk 19-Nov-18 Introduction to GAMIT/GLOBK

Earth Orientation Parameters (EOP)
Apriori uncertainties apr_wob <X> <Y> <Xdot> <Ydot> X, Y pole position apriori sigma (mas) Xdot Ydot apriori sigma for rate of change (mas/day) apr_ut1 <sut1> <lod> < sut1 > in mas, < lod > in (mas/day) Process noise has same form mar_wob <RWX> <RWY> <RWXd> <RWYd> units are (mas2)/yr and (mas/day)2/yr mar_ut1 <RW UT1> <RW lod> Nominally EOP are well known today (0.2 mas typically), however in many analyses we like to keep these parameter loose to allow common-mode local rotation (for IGS runs still needed) 19-Nov-18 Introduction to GAMIT/GLOBK

GLORG: pos_org and rate_org
The two commands determine how coordinate system will be realized from loose globk analysis. Class of parameters: Xtran ytran ztran – allows translation Xrot yrot zrot – allows rotation Scale – allows rescaling of system Strictly when transation used the apr_tran and mar_tran commands should be used in globk analysis. (We are still not sure this is best thing to do) Absolutely if scale used, apr_scale and mar_scale commands should be used in globk 19-Nov-18 Introduction to GAMIT/GLOBK

Defining coordinate system in globk
To define a coordinate system need origin, orientation and possibly scale Strictly for GPS scale should be defined but systematic errors in the position of the phase center of satellites cause a scale error and scale rate error (due to evolving GPS constellation: Problem should be reduced with new absolute phase center model but all old data will need to be reprocessed once new orbits have been generated). Strictly, origin is also defined but mis-modeled perturbation on satellite orbits can cause shift in origin 19-Nov-18 Introduction to GAMIT/GLOBK

GLORG Rotation If rotation used in pos_org, EOPs must be loose in globk (apr_wob/mar_wob and apr_ut1/mar_ut1) If rotation not used then EOPs should be constrained (Often good on small networks) but position errors grow near edges of network There can be problems with zrot terms because of differences between the node position of the satellites and UT1 tables used in globk analysis. Rotation rate: EOP tables are in Nuvel-not-net-rotation frame. If analysis done in another frame (e.g., North America fixed) rotation rates should be allowed or EOP file generated in corrected frame (no module yet to do this but will be done soon). 19-Nov-18 Introduction to GAMIT/GLOBK

glorg coordinate definition
The glorg module in globk defines the coordinate system by applying rotation, translation, and scale to best align with coordinates of a selected set of stations: Algorithm assumes these parameters are loosely constrained. Apriori coordinates and velocities define frame. User chooses which of the translation, rotation and scale are included If scale is used, it must be explicitly estimated in globk For velocity definition: Same generalized system can be applied i.e. rates of translation, rotation, scale aligned with velocities of sites. In general: No specific station coordinates are tightly constrained 19-Nov-18 Introduction to GAMIT/GLOBK

Summary Basics of Kalman filtering Inputs to globk Control of globk Glorg applications Basic programs in the globk suite 19-Nov-18 Introduction to GAMIT/GLOBK

Common applications of GLOBK

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