Introduction to GAMIT/GLOBK GLOBK Theory and Solution ...geoweb.mit.edu/~tah/IndianGPSCourse/India_lec10.pdfchange in process over an interval of time oVariance grows linearly with
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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
GAMIT/GLOBK Lec10 3
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
GAMIT/GLOBK Lec10 5
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
GAMIT/GLOBK Lec10 6
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)
GAMIT/GLOBK Lec10 7
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
GAMIT/GLOBK Lec10 8
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
GAMIT/GLOBK Lec10 9
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
GAMIT/GLOBK Lec10 10
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
GAMIT/GLOBK Lec10 11
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
GAMIT/GLOBK Lec10 12
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
GAMIT/GLOBK Lec10 13
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
GAMIT/GLOBK Lec10 14
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
GAMIT/GLOBK Lec10 15
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
GAMIT/GLOBK Lec10 16
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
GAMIT/GLOBK Lec10 17
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.
GAMIT/GLOBK Lec10 18
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
GAMIT/GLOBK Lec10 19
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
GAMIT/GLOBK Lec10 20
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
GAMIT/GLOBK Lec10 21
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
GAMIT/GLOBK Lec10 22
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
GAMIT/GLOBK Lec10 23
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)
GAMIT/GLOBK Lec10 24
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]
GAMIT/GLOBK Lec10 25
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)
GAMIT/GLOBK Lec10 26
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
GAMIT/GLOBK Lec10 27
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
GAMIT/GLOBK Lec10 28
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
GAMIT/GLOBK Lec10 29
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
GAMIT/GLOBK Lec10 30
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
GAMIT/GLOBK Lec10 31
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
GAMIT/GLOBK Lec10 32
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)
GAMIT/GLOBK Lec10 33
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.
GAMIT/GLOBK Lec10 34
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
GAMIT/GLOBK Lec10 35
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]
GAMIT/GLOBK Lec10 36
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]
GAMIT/GLOBK Lec10 37
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
GAMIT/GLOBK Lec10 38
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
GAMIT/GLOBK Lec10 39
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)
GAMIT/GLOBK Lec10 40
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
GAMIT/GLOBK Lec10 41
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
GAMIT/GLOBK Lec10 42
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
GAMIT/GLOBK Lec10 43
Summary
o Basics of Kalman filteringo Inputs to globko Control of globko Basic programs in the globk suite
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