Common applications of GLOBK

1. 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 Introduction to GAMIT/GLOBK

2. 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 Introduction to GAMIT/GLOBK

3. 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) Introduction to GAMIT/GLOBK

4. 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 Introduction to GAMIT/GLOBK

5. 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 Introduction to GAMIT/GLOBK

6. 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 Introduction to GAMIT/GLOBK

7. 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 Introduction to GAMIT/GLOBK

8. 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) Introduction to GAMIT/GLOBK

9. 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 Introduction to GAMIT/GLOBK

10. 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 mustbe kept loose in globk ; if rotation or scale is not estimated in glorg, it must be tightly constrained in globk Introduction to GAMIT/GLOBK

11. EOP statistics • Normally used in two forms: • Global network of stations • apr_wob 10 10 1 1 • apr_ut1 10 1 • Regional network (constrained). When constrained this way system is not free to rotate (see pos_org in glorg). • apr_wob 0.2 0.2 0.02 0.02 • apr_ut1 0.2 0.02 • 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). Introduction to GAMIT/GLOBK

12. 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) Introduction to GAMIT/GLOBK

13. 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 Introduction to GAMIT/GLOBK

14. 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-6 0 0 0 • Can also add random noise (units are m) sig_neu all .001 .001 .003 sig_neu ankr .005 .005 .020 2002 11 15 0 0 2002 11 30 24 0 sig_neu HEMED0504 .010 .010 .1 Introduction to GAMIT/GLOBK

15. 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) Introduction to GAMIT/GLOBK

16. 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 Introduction to GAMIT/GLOBK

17. 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 Introduction to GAMIT/GLOBK

18. 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 Introduction to GAMIT/GLOBK

19. 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 Introduction to GAMIT/GLOBK

20. 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. Introduction to GAMIT/GLOBK

21. 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] Introduction to GAMIT/GLOBK

22. Introduction to GAMIT/GLOBK

23. 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) Introduction to GAMIT/GLOBK

24. 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) Introduction to GAMIT/GLOBK

25. 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. Introduction to GAMIT/GLOBK

26. 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 Introduction to GAMIT/GLOBK

27. 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 Introduction to GAMIT/GLOBK

28. 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. Introduction to GAMIT/GLOBK

29. 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. Introduction to GAMIT/GLOBK

30. 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. Introduction to GAMIT/GLOBK

31. 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). Introduction to GAMIT/GLOBK

32. 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 Introduction to GAMIT/GLOBK

33. 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 card @ at end of line can be used to apply to multiple sites (e.g., AOA1_@ 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 0 0 0 used] Introduction to GAMIT/GLOBK

34. 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. Introduction to GAMIT/GLOBK

35. 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 Introduction to GAMIT/GLOBK

36. 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) Introduction to GAMIT/GLOBK

37. 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 Introduction to GAMIT/GLOBK

38. 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 Introduction to GAMIT/GLOBK

39. 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). Introduction to GAMIT/GLOBK

40. 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 Introduction to GAMIT/GLOBK

41. Summary • Basics of Kalman filtering • Inputs to globk • Control of globk • Glorg applications • Basic programs in the globk suite Introduction to GAMIT/GLOBK