Transcript PowerPoint Presentation - 12.215 Modern Navigation

User Controllable Options in GAMIT
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Station/session information
Models for orbits and station motion
Models for signal propagation
Controls for cycle-slip repair
Sampling and estimation controls
A priori values for coordinates and orbits
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Primary User files
– station.info
• receiver type, antenna type and height as f(t)
– guess.rcvant
• Converts RINEX header to GAMIT standard
– L-file
• Prior estimates of station coordinates
– sestbl.
• Controls modeling and estimation for session
– sittbl.
• Site specific controls
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station.info
– Fixed format file with station information
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*TRCK SITE Station Name Ant Ht Ant N Ant E \
7ODM 7ODM Seven Oaks Dam 0.0083 0.0000 0.0000 \
Rcvr AntCod HtCod Vers \
ASHZ12 ATDMRB DHPAB 9.10 \
• Year Doy SN Start Stop
• 2000 110 0 00 00 00 24 00 00
• (\ = line break for this display)
– This file must be sorted by TRCK, then epoch
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TRCK SITE station_name
• TRCK and SITE
– 4-character code
– match the 4-char code in RINEX file name
– TRCK = SITE for static analysis
• Change for kinematic analysis
– File must be sorted by this field, then epoch
• station_name
– is a long (12-char) description
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AntHt, N and E, HtCod
• AntHt
– Raw antenna height as measured
– Critical measurement!
• HtCod
– Defines geometry of AntHt measurement
– DHPAB is RINEX standard is vertical height to antenna
reference point (ARP)
• N and E offsets
– e.g., uncalibrated tribrach
– rarely used
– occupied point w.r.t. benchmark
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RCVR Vers
• RCVR
– 6-character codes for the receiver type
– not critical except for some old receivers
– or "buggy" firmware versions
• Vers
– version number of firmware in the receiver
– Should be correct to handle SNR coding properly
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AntCode
• AntCod and HtCod are critical
– Sets phase center model
– conversion of antenna height measurement
– SLBGP -- Slant bottom ground plane
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Epoch
• year and doy specify year and day of year when the
values apply
• times set part of day
– (if it changes during UTC day)
• This representation will be augmented in future
version of GAMIT
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gg/tables/rcvant.dat
• File contains all receivers and antennas known to
GAMIT
• Translates user-specified 6-character code to IGS
SINEX standard.
• The file in templates directory provides mapping from
RINEX header information to 6-char codes.
• Example lines
– rcv ASHTECH^Z-XII ASHZ12
– rcv Z-XII3 ASHZ12
– swv 5F
1.00
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gg/templates/guess_rcvant.dat
• Explanation given at top of file
• ^ used a represent space
• Sometimes need to be careful that pattern correctly
gets correct type. Should not be a problem for IGS
rinex files
• default lines allowed, but be careful
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Updating station.info
• RINEX headers will be used to update station.info
unless:
– An entry already exists for the day being processed
– stinf_unique is set to -u in process.defaults and
entry has not changed
– xstinfo set for a site in sites.defaults
• An error here can be fatal
– If systematic patterns appear in sky map residual
plots, antenna type may be wrong
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Apriori coordinates
– L-file
• Geocentric latitude, longitude and radius
– (Spherical, not ellipsoidal)
• Coordinates (no velocities) for a single epoch
• Read by model and solve
– sh_gamit calls gapr_to_l
• Creates an L-file from (time-dependent) coordinates and
velocities from globk apr file
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Apriori coordinates (2)
• sh_gamit merges entries from existing lfile for sites
not in apriori file
• If script still can’t find coordinates:
– Uses pseudorange data in rinex file to generate
point position or differential range position relative
to site in sites.defaults
– Use Rinex header coordinates (can block this by
setting use_rxc N in process.defaults)
– During the sh_gamit run, the coordinates are
updated if they are in error by > 30 cm
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sh_gamit runs autcln
• a priori coordinates need to be < 10 m
– with default settings
– autcln can be "de-tuned" to allow worse
• Post-2000, No SA:
– receiver-estimated coordinates fine
• Pre-2000 with SA:
– differential range position needed
• Common problem with campaign data
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sestbl. controls
• file resides in tables directory
• important options:
– parameters for running model
– estimation procedures for solve
• some site-specific info also in sittbl.
– if conflict, sittbl. takes precedence (automatic)
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Primary sestbl. entries
• Satellite constraints
– defaults for post-IGS (1992) regional data
– for broadcast ephemeris
• used, increase 6 Keplerian elements to 1 ppm
• increase radiation parameters to 100 (%)
• Type of Analysis 0-ITER (keep)
– Assumes a-priori coordinates are good
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sestbl. observables
• LC_HELP
– uses pseudoranges to help fix ambiguities.
– works well for regional networks
• LC_only
– uses phase data only to fix ambiguities
– quicker, works well for global networks
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sestbl. observables
(continued)
• L1, L1+L2
– Single frequency phase combinations
– best for short baselines (e.g., ties)
– ionospheric effects are 1-10 ppm
– therefore 1-10 mm per km of site separation
– But use caution with mixed antenna types
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Decimation
• Speeds up processing
– factor 4 usual for 30-second data
• Our practice is to
– use short term position scatter with sigma at this
decimation and data noise sigmas
– This has little effect on positions for sampling up to
5 minutes
• Uncertainty (sigma)
– goes as square root of number of data
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autcln control options
• Command file name autcln.cmd keep
• AUTCLN Postfit:
– Y runs prefit run to get data noise model
– R iterates if pre-fit RMS is too high
• Use N-file:
– Y autcln computes an elevation angle dependent
noise estimates for each site, assuming
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data variance = A2 + (B/sin(elev))2
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autcln control options
(continued)
• Delete AUTCLN input C-files
– Controls speed and size of run
– YES -- deletes all cfiles during run. Re-runs model
between cleaning and estimation. Needed if bad
apriori coordinates. Uses least disk space
– Intermediate -- Deletes intermediate C-file, similar
to yes
– NO -- Keeps C-files and uses more disk space, but
faster. Good for continuous array processing.
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Atmospheric delay estimation
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Zenith delays and gradients
Number of points in piecewise continuous function
Overall constraint
First order Gauss Markov parameters (variance and
correlation time)
• Number of gradient parameters
• overall constraint
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Atmospheric delays
• Defaults are good for most conditions
• If turbulent conditions, then constraints should be
loosened (increased numerical values)
• Elevation cutoff angle (with N-file not so critical)
• Autcln should be consistent (cleaning minimum
elevation < estimation minimum elevation)
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model parameters
• Antenna Model
– ELEV is most common
– Important when mixing antenna types
• Tide Model (1 bit for each option)
– 1 -- Earth tide
– 2 -- Frequency dependent K1
– 4 -- Pole tide (IGS/ITRF standard)
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Can also be applied in GLOBK
– 8 -- Ocean loading (need ocean grid file)
– Binary sum defines the model, e.g., 1+5=6
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model options: EOP, Yaw
• EOP model choices
– Diurnal and semidiurnal modes
– 1 -- Pole
– 2 -- UT1
– 4 -- Use Ray model (VLBI model if bit2=0)
• YAW model
– to handle satellite rotation
– default is Y
– some problems with old data during and after
eclipses
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solve options
• Controls how solve performs the least squares
estimation
• Estimate_EOP
– binary coded
– can be constrained later in globk run
• UT1 and wobble constraints.
– usually done later in GLOBK
– but can be tightened in solve for regional analysis
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Cleaning options
• Quick-pre
– sets estimation type for the prefit run
– can be made fast with decimation and observable
• Delete eclipse data
– POST -- 30 minutes after eclipse
– ALL -- POST but data in eclipse
– Mainly an issue for global data sets
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Ambiquity resolution
• Defaults optimized for regional networks (<1000 km).
Default is 500.
• Wide lane (L1-L2) and narrow lane (L1)
• Ionospheric constraint plus range data
• default values work well (see Section 5.5)
• Constraints on good apriori coordinates help
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sittbl.
site-dependent options
• Normally not changed
• Mainly constraints on apriori apriori station
coordinates
• Distribution example has IGS sites plus others
• Takes precedence over sestbl.
• Not all columns are required
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Summary
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User-controllable files add flexibility
Modifications seldom required
Distribution example is for regional net
Some changes appropriate for
– global data processing
– operation near real-time
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