Transcript PowerPoint Presentation - 12.215 Modern Navigation

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
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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
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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)
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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
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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
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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
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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
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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 standalone)
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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 hfiles
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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
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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).
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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)
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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
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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
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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)
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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
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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
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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
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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
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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.
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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]
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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)
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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)
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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.
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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:
•
•
•
•
•
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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
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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
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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.
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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.
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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.
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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).
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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
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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]
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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.
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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
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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 <ut1> <lod>
– < ut1 > 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)
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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
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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
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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).
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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
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Summary
•
•
•
•
•
Basics of Kalman filtering
Inputs to globk
Control of globk
Glorg applications
Basic programs in the globk suite
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