Transcript PowerPoint Presentation - 12.215 Modern Navigation

GLOBK Theory and Solution Types
Kalman filtering
Stochastic processes
Applications
Summary of Use of GLOBK
• GAMIT output is an “h-” file of loosely constrained
estimates and covariances, used as input (quasi-)
observations to GLOBK
• GAMIT ascii h-files converted to binary h-files for input
to GLOBK
• GLOBK combines h-files from several networks for a
single day and h-files from multiple epochs to estimate
positions in a time series or average velocities
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Motivation
• GLOBK is quicker than GAMIT
– Typically perform many GLOBK runs to test
different hypotheses and correct problems in
original GAMIT analyses with out re-running
GAMIT.
• Ultimately once all is understood, GAMIT is rerun and
the process repeated for the final results
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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
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Common applications
of GLOBK
• Repeatability analysis (glred)
– individual sessions
– combined files
• Combine sessions to get average position over
experiment
– connects sites observed separately
• Combine averaged files together to estimate velocities
– and/or earthquake offsets
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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 sites
– can help avoid contaminating solution
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Preparing to run GLOBK
• Shell script sh_glred
– automates standard runs with globk
– useful to start
– assumes internet access
– but can be run without internet
• Globk needs:
– Binary h-files
• written by htoglb from solve’s output
– A command file to tell it what to do
• e.g., globk.cmd
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Binary h-files
• Generated with htoglb
– from the h<expt>a.<yy><doy> files
• solve writes these in day dir
– or from SINEX files
• available from IGS
• and soon for IVS for VLBI and ILS for SLR results
– Program detects file type
• Or written by globk itself
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running htoglb
• htoglb dir ephfile[options] file_list
– dir is directory where binary files will be written
– ephfile is satellite orbit file
• not used any more, because of make_svs command
– options are optional options
– file_list a list of ascii files
• usually with UNIX wild cards
• or generated from ls
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running htoglb
• htoglb glbf glbf/india.svs ????_???/hgps?a.*
– run this from processing directory
– converts all ascii hfiles for our runs
– puts the binary H-files in directory glbf
• Some options:
– -n sets name format
– -m allocates more memory
– (only needed for very large SINEX files)
– -c replaces SINEX constraints
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GLOBK command files
• Example in ~/gg/templates/globk_comb.cmd
• Basic features of command files
– These are also common to other input files used by
globk
– Any non-blank character in column 1 denotes
comment
– Only minimum redundant part of command needed
– In many cases, not all arguments need be given
• Examine the command file from templates
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Defining a coordinate system in
GLOBK
• To define a coordinate system need
– origin (3 parameters)
• Theoretically, origin is defined but mis-modeled
perturbation on satellite orbits can cause shift in origin
– orientation (3 parameters)
– scale (1 parameter)
• Theoretically, scale should be defined but systematic errors
in the position of the phase center of satellites can cause a
scale error
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Defining a coordinate
system with glorg
• The glorg module of GLOBK applies rotation, translation, and
scale to best align estimated coordinates with prior values for a
selected set of stations
– this process is called “stabilization” (pos_org)
– subset of stations is the “stabilization list” (use_site)
• User chooses which parameters are free (estimated)
– translation xrot yrot zrot
– rotation
xtran ytran ztran
– scale
• If scale is used, it should be explicitly estimated in globk
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Velocity origin
• Same approach can be applied to site velocities, i.e. rates of
– translation
– rotation
– scale
• Use rate_org command with same key words
• This will align the estimated station velocities with prior values for
(the same) set of selected sites
• No specific station coordinates are tightly constrained
• We call this “velocity stabilization” in jargon.
• In papers we write, “velocities with respect to a set of stations on
stable North America”
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Structure of GLOBK
• GLOBK is a suite of modules
– can be run end-to-end as the globk module
– or run individually, e.g.,
• glred (reduce one day at a time)
• glorg (origin)
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Program sequence
• globk
• glinit
•
h-files
•
• glfor
• glbak
• glsave
• glout
• glorg
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Main controlling program that calls other modules
Initialization program
reads the headers of all the binary
to determine their contents
Forward kalman filter
Backards running filter and smoother
Saves combined binary h-files
writes output to files and/or screen
defines origin and coordinate system
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Stand-alone programs
• glorg (and sometimes glsave) can be run as separate
programs, typically after globk has finished
• or they can be run via globk by placing their
commands globk.cmd file
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Associated programs
• glist
•
solution
• glbtosnx
•
H-files
• hfupd
in
•
• glred
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lists the contents of a series of H-files
useful to check input before
generates SINEX files from binary H-files
only way to view header of binary
updates binary h-files for changes
station info or SINEX header file
(distributed by IGS)
runs globk multiple times
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Running globk
• globk crt print_file log_file gdl_file cmd_file
•
•
•
•
•
crt
print_file
log_file
gdl_file
cmd_file
= 6 for screen output
output print file name (can be 6)
output log file name (can be 6)
input file listing H-file names to process
input command file name
• If you can’t remember this order, just type “globk” to get the
help message.
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globk files
• .gdl
– lists all H-file names to include in solution
– run 'ls' on the directory containing the binary H-files
• .cmd
– contains commands
– user modifies with a text editor
– based on template
• .prt and .log
– print and log files written by globk
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Main globk commands
• globk uses three "scratch" files which can be explicitly
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 as stand-alone module, the same
com_file command must appear in both the
command file for globk and the command file for the
(subsequent) glorg run
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apr_xxx
• This command will free (estimate) a parameter.
– If this command is absent, the corresponding
parameter will be held fixed to its apriori value
– If zero is given as apriori sigma, then parameter is
not estimated (effectively left unconstrained)
– To force a parameter to its apriori value, use F as
sigma
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Site position estimation
apr_neu
• apr_neu site sigN sigE sigU sigVN sigVE sigVU
– site is site name; may be all to apply to all stations
– sigN sigE sigU apriori sigmas on position in meters
– sigVN sigVE sigVU apriori velocity sigmas in m/yr
• apr_neu SITE 10 10 10 F 0.1 0
– set prior sigma for N, E, U positions to 10 meters
each
– force the north velocity to its apriori value
– set the prior sigma for the east velocity to 0.1 m/yr
– do not estimate a vertical velocity
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Estimating site position
stochastically mar_neu
• Markov random walk process
• mar_neu site rwN rwE rwU rwVN rwVE rwVU
– site
station name, may be all
– rwN rwE rwU random walk for positions (m^2/yr)
– rwVN rwVE rwVU
random walk for velocities
»
»
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in (m/yr)^2/yr
usually use 0 0 0
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Estimating satellite orbit
parameters apr_svs
• Set apriori sigma for space vehicle parameters
• apr_svs PRN X Y Z Vx Vy Vz rad_parms
– PRN
satellite identification PRN_nn or
ALL
–X Y Z
Position sigma (3 values) (m)
– Vx Vy Vz Velocity sigma (3 values) (mm/s)
– rad_parms
Radiation parameter sigmas
»
»
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up to 11 values
fraction 0-1
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Satellite orbit estimation
apr_svs (continued)
• Have global GPS sites to constrain orbits
• apr_svs all 100 100 100 10 10 10 1R
• Local data only, constrain orbit to apriori value
– apr_svs all 0.1 0.1 0.1 0.01 0.01 0.01 0.01R
– R at end of line means remaining radiation
parameters
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EOP parameters
• Apriori uncertainties
– apr_wob <X> <Y> <Xdot> <Ydot>
– X Y pole position (mas)
– Xdot Ydot rate of change (mas/day)
– apr_ut1 <ut1> <ut1 dot>
– <ut1> in mas, <ut1 dot> in (mas/day)
• Process noise has same form
– mar_wob <RWX> <RWY> <RWXd> <RWYd>
– units are (mas2)/yr and (mas/day)2/yr
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EOP parameters
(continued)
• mar_ut1 for for ut1 (mas2) and (mas/day)2/yr
• Normally used in two forms:
– Global network of stations
– apr_wob 10 10 1 1
– apr_ut1 10 1
– Regional network (constrained)
– apr_wob 0.2 0.2 0.02 0.02
– apr_ut1 0.2 0.02
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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
if constraints on UT1 are applied.
• If local processing, then should be OK
• If orbits were determined with different EOP tables,
then UT1 should be loosened
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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
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File commands
• A number of commands are used to control the files
read 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 decimal years
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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 coordinates are used
(no velocities)
• EXTENDED option allows more complex behaviors
(see globk.hlp)
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Orbit files
• When single days are processed, orbits from GAMIT
solution will be used by default
• For multiple days, with globk, the make_svs command
is needed to generate an orbit file.
• Form:
• make_svs <file name>
• <file name> will be overwritten
• Command must be near top of command file.
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EOP files
– GAMIT EOP are used by default, but can be
changed with in_pmu command
– Form:
– in_pmu <file name>
– Format of file is
– yy mm dd hr min Xpole +- Ypole +- UT1-AT +– Must be uniformly spaced
– Pole in arc-seconds, UT1 in time-seconds
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Earthquake files
• It is possible to automatically account for displacement
caused by earthquakes with the earthquake file
• Main functions:
– specify earthquakes with 2-char code
– rename sites
• Rename command:
• Rename <old> <new> [HFile code] [Epoch ranges]
[Position shift]
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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>
• The rename option cause site to renamed from
xxxx_GPS to xxxx_G[Code]
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GLORG
• Glorg allows coordinate systems to be defined by
applying explicitly rotations and translations rather
than tightly constraining some stations
• It can be run as a separate program or during the
globk run itself
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Glorg imbedded commands
• 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
• Next lecture discussed glorg
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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
• 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
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PRT_OPT, ORG_OPT
options
–
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 -- Echo globk command file into output file
• Main use of these options is to keep output files small
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Command file layout
– In general, the commands in globk can appear in
any order
– They can be repeated with later version replacing
earlier ones
• e.g. apr_neu all 10 10 10 0 0 0
• apr_neu iisc_gps 0.01 0.01 0.01 0 0 0
• would use 10 m constraints on all sites, except IISC which
would be 10 mm
– The following commands must appear before
others: com_file, srt_file, make_svs, eq_file
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Summary
•
•
•
•
Basics of Kalman filtering
Inputs to globk
Control of globk
Basic programs in the globk suite
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