introduction to gamit/globk globk theory and solution...

GAMIT/GLOBK Lec10 1

Introduction toGAMIT/GLOBK

GLOBK Theory and SolutionTypes

Lecture 10

GAMIT/GLOBK Lec10 2

Overviewo Basics of Kalman filteringo Types of "data" input to globko Control files for globko Basic globk programs

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Kalman Filtering

o Estimation method in which parameterscan random processes

o Examples: polar motion and UT1,radiation pressure effects on satellites

o Nearly all parameters in globk can bestochastic or deterministic

o Statistical character set by apr_XXX andmar_XXX commands

GAMIT/GLOBK Lec10 4

Stochastic processes

o Stochastic models in globk are randomwalks characterized by variance ofchange in process over an interval oftime

o Variance grows linearly with time(standard deviation grows as squareroot of time)

o If process noise is zero, then classed asdeterministic

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Common applications of globk

o Combine sessions to get averageposition over experiment

l Allows connection between sites that werenot simultaneously observed

o Combine averaged files together toestimate velocities

l Other parameters can also estimated suchas earthquake offsets

o Analysis of individual sessions andcombined files for repeatability

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Things globk can not do

o Linear model, so non-linear effects cannot be removed

o Fix errors in original analysis such ascycle slips or antenna phase centermodels

l Sites can be deleted which often stops effecton other stations

l resolve ambiguities (would make files toolarge)

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Preparing globk

o sh_glred automates standard runs withglobk and can be used as a startingpoint.

l Assumes internet access but can be runwithout

o Globk needs:l Binary h-files (htoglb)l command file to tell it what to do

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Binary h-files

o Generated with htoglb from theh<expt>a.<yy><doy> files in processingday directories

o htoglb run with SINEX fileso Program detects which type of file is

given.o SINEX files available from IGS and soon

for IVS for VLBI and ILS for SLR resultso Globk itself can write binary h-files

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HTOGLB

o Running htoglbo Runstring:

l htoglb <dir> <ephemeris file> [options] <listof ascii files>

l dir is directory where binary files wll bewritten

l ephemeris file is satellite orbit file (not usedany more, make_svs)

l options are optional optionsl list of ascii files, usually with UNIX wild cards

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HTOGLB

o For example: From processing directoryl htoglb glbf glbf/india.svs ????_???/hgps?a.*l converts all ascii hfiles for our runs and puts

the binary files in directory glbfo Some options:

l -n sets name format (htoglb.hlp)l -m allocates more memory (only needed for

very large sinex files)l -c replaced sinex constraints


Globk command file

o Example given in gg/templates/globk_comb.cmdo Basic features of command files (also common to

other input files used by globk)l Character in column 1 denotes commentl only minimum redundant part of command neededl In many cases, not all arguments need be given

o Show the command file fromtemplates


Defining coordinate systemin globk

o To define a coordinate system needorigin, orientation and possibly scale

o Strictly for GPS scale should be definedbut systematic errors in the position ofthe phase center of satellites can causea scale error

o Strictly, origin is also defined but mis-modeled perturbation on satellite orbitscan cause shift in origin


glorg coordinate definition

o The glorg module in globk defines thecoordinate system by applying rotation,translation, and scale to best allign withcoordinates of a selected set of stations

o User chooses which of the translation,rotation and scale are included

o If scale is used, it should be explicitlyestimated in globk


Velocity origin

o Same generalized system can beapplied to velocities ie. rates oftranslation, rotation, scale aligned withvelocities of sites.

o No specific station coordinates aretightly constrained


Structure of globk

o Globk is a series of programs that arecombined in a single program

o The invidual modules act either assubroutines or as programs (ie. some ofthe modules can be run by themselves


Program sequence

o The sequence of programs are:n globk -- Main controling program that calls other

modulesn glinit -- Initialization program, reads the headers of

all the binary h-files to determine their contentsn glfor -- Forward kalman filtern glbak -- Backards running filter and smoothern glsave -- Saves combined binary h-filesn glout -- basic output programn glorg -- origin definition program


Stand-alone programs

o glsave and glorg are often run asseparate programs

o Commands can be put in the globkcommand that will run these modules

o Sometimes these command are notincluded and in most cases they can berun after the globk program completesrunning.


Associated programs

o Other program associated with globkl glist -- lists the contents of a series of hfilesl glbtosnx -- Generates SINEX files from

binary hfilesl hfupd -- Updates binary h-files for changes in

station info or sinex header file (distributed byIGS)

l glred -- Convenient way of running globkmultiple times


Running globk

o Typing globk will list the helpo Runstring:

n globk <crt> <print file> <log file> <gdl file> <globkcommand file>

n where <crt> = 6 (screen output)n <print file> -- Print file name (can be 6 for screen)n <log file> -- log file name (can be 6)n <gdl file> -- file containing list of hfiles to processn <globk command file> -- command file name


globk files

o The gdl file is generated normally withan 'ls' of the directory containing thebinary hfiles

o command file is created with an editor(can be based on templates version offile)

o print and log files are written by globk


Main globk commands

o Commands commonly used:o Globk uses three "scratch" files which

can be explicilty namedn com_file -- Common file contains information about

runn srt_file -- binary file with time-sorted list of hfilesn sol_file -- binary file with solution and covariance

matrixo To use glorg stand-alone, com_file

command must be used


Estimation commands rules

o For a parmeter to estimated in globk,apr_xx command must be used

o If zero given as aprori sigma, thenparameter is not estimated (effectivelyleft unconstrained)

o To force a parameter to apriori value, Fis used as sigma

o eg, apr_neu SITE 10 10 10 F F Fo would force the velovity to apriori value


Estimation commands

o Site position estimationl apr_neu <site> <sigN> <sigE> <sigU>

<sigVN> <sigVE> <sigVU>l site is site name; maybe all to apply to all

stationsl <sigN> <sigE> <sigU> aprior sigma on

position (m)l <sigVN> <sigVE> <sigVU> apriori sigma on

velocities (m/yr)


Site position estimation

o Stochatic noise processl mar_neu <site> <RWN> <RWE> <RWU>

<RWVN> <RWVE> <RWVU>l site name, may be alll <RWN> <RWE> <RWU> Random walk

positions (m^2/yr)l <RWVN> <RWVE> <RWVU> Random walk

velocities ((m/yr)^2/yr) [Normally 0 0 0 used]


Estimation commands

o Satellites Orbitl apr_svs <PRN> <X Y Z> <Vx Vy Vz>

<Radiation parameters>l <PRN> is PRN_NN or all (normal)l <X Y Z> Position sigma (3 values) (m)l <Vx Vy Vz> Velocity sigma (3 values) (mm/s)l Radiation pameter sigmas (upto 11 values)

(fraction 0-1)


Satellite orbit parameters

o Normal ly apr_svs only used in to twoforms:

l When global GPS sites included so orbit canbe estimated well

l apr_svs all 100 100 100 10 10 10 1Rl When only local data used and constrain to

apriori orbitl apr_svs all 0.1 0.1 0.1 0.01 0.01 0.01 0.01Rl R at end of line means remaining radiation

parameters


EOP parameters

o Apriori uncertaintiesl apr_wob <X> <Y> <Xdot> <Ydot>l X Y pole position (mas)l Xdot Ydot rate of change (mas/day)l apr_ut1 <ut1> <ut1 dot>l <ut1> in mas, <ut1 dot> in (mas/day)

o Process noise has same forml mar_wob <RWX> <RWY> <RWXd>

<RWYd>l units are (mas2)/yr and (mas/day)2/yr


EOP statistics

o mar_ut1 for for ut1 (mas2) and(mas/day)2/yr

o Normally used in two forms:l Global network of stationsl apr_wob 10 10 1 1l apr_ut1 10 1l Regional network (constrained)l apr_wob 0.2 0.2 0.02 0.02l apr_ut1 0.2 0.02


UT1 issues

o Some care needs to be used with UT1becuase it cannot be separated from thenodes of the satellites orbits

o UT1 tables and orbits must have usedthe same frame for constraints on UT1to applied.

o If local processing, then should be OKo If orbits were determined with different

EOP tables, then UT1 should beloosened


Frame estimation commands

o apr_tran <X YZ> <Vx Vy Vz> -- estimatetranslation of coordinate system

o apr_scale <ppb> <ppb/yr> -- estimatescale and scale rate

o mar_tran and mar_scale specify theprocess noise

o Normally only used in global networks


File commands

o A number of commands are usedcontrol the files used by globk

o apr_file <name> lets a new aprioricoordinate file be used

o Format is:n Site_name X Y Z Vx Vy Vz epochn Site names are 8 characters, for GPS

ABCD_GPSn X Y Z are geocenter Cartesian (m)n Velocities are m/yrn Epoch is deciminal years


Apriori position files

o apr_files commands can be issuedmultiple times with the latest valuestaken

o If not specified, GAMIT apriori's areused (no velocities)

o EXTENDED option allows morecomplex behaviors (see globk.hlp)


Orbit files

o When single days are processed, orbitsfrom gamit will be used by default

o For multiple days, with globk, themake_svs command is needed togenerate an orbit file.

o Form:o make_svs <file name>o <file name> will be overwritteno Command must be near top of

command file.


EOP files

l GAMIT EOP are used by default, but can bechanged with in_pmu command

l Form:l in_pmu <file name>l Format of file isl yy mm dd hr min Xpole +- Ypole +- UT1-AT

+-l Must be uniformly spacedl Pole in arc-seconds, UT1 in time-seconds


Earthquake files

o It is possible to automatic account fordisplacement caused by earthquakeswith the earthquake file

o To main functions:l Earthquakes specified by 2-char codel renames of sites

o Rename command:n Rename <old> <new> [HFile code] [Epoch ranges]

[Position shift]


Earthquakes in eq_file

o For earthquake:n eq_def <code> Lat Long Radius Depth

Epochn eq_cosei <code> <Static Variance>

<distance dependent variances>n eq_post <code> <dur> <Static RW>

<distance dependent RW>n eq_rename <code>

o The rename option cause site torenamed from xxxx_GPS toxxxx_G[Code]


GLORG

o Glorg allows coordinates systems to bedefined by applying explicitly rotationsand translations rather than tightlyconstraining some stations

o It can be run as a separate program orduring the globk run itself


Glorg imedded commands

o The globk command file imbedded glorgcommands are:

o org_cmd <glorg command file name>o org_opt <Options for output>o org_out <output file name>o If org_out is not given then the extent on

the print file name is replaced with .orgo Next lecture discussed glorg


Miscellaneous commands

o max_chi <max chi**2 Increment> <maxprefit difference> <max rotation>

o allows automatic deleting of bad h-filesand bad coordinates

o app_ptid allows applying the pole tidecorrection if not included in gamit run.

o (Careful with SINEX files, since thesedon't specify if correction has beenapplied)


Miscellaneos commands

o crt_opt, prt_opt, org_opt specify outputoptions for screen, print and org files

o glorg help gives all options, main onesare:

l ERAS -- erase file before writing (normallyfiles appended)

l NOPR -- Do not write outputl BLEN -- Baseline lengthsl BRAT -- baseline rates when velocities

estimated


PRT_OPT, ORG_OPT options

l VSUM -- Lat/long summary of velocity(needed to plot velocities)

l PSUM -- Lat/long position summaryl GDLF --Include list of hfiles and chi**2

increments from runl CMDS -- Echo globk command file into

output fileo Main use of these options is to keep

output files small


Command file layout

l In general, the commands in globk canappear in any order

l They can be repeated with later versionreplacing earlier onesn e.g. apr_neu all 10 10 10 0 0 0n apr_neu iisc_gps 0.01 0.01 0.01 0 0 0n would use 10 m constraints on all sites, except

IISC which would be 10 mml The following commands must appear before

others: com_file, srt_file, make_svs, eq_file


Summary

o Basics of Kalman filteringo Inputs to globko Control of globko Basic programs in the globk suite

introduction to gamit/globk globk theory and solution...

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