Transcript PowerPoint Presentation - 12.215 Modern Navigation

Tuning AUTCLN for editing
Autcln basics
• Controlled by the autcln.cmd file
• The defaults in the program are set for data from
modern receivers
• These default values need not be included in the
command file
– Post-fit cleaning is primary exception
• Can be "tuned" extensively
– Very useful for data from older receivers
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Basic aims and operation
• Aims:
– Generate a set of one-way phase time series in
which all cycle slips are either
• corrected (with integer step functions)
• flagged (to introduce real-valued offset)
– “Bias flags” are used for cycle slips that cannot be
resolved to integer values
– Generate one-way phase residuals that can be
used for data weighting
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How autcln works
• (1) Generate models for receiver and satellite clocks
• Measure clock offset epoch-by-epoch using pseudorange
data
• Align offsets with the polynomial estimated from the K- and
J-files.
• (2) Identify and flag possible jumps in phase data
• using wide-lane (WL) when available
• and/or ionospheric-delay (LG) phase
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How autcln works
(II)
• (3) Align the phase data with the range clock solution
• look for large slips in the phase data
• look for jumps in the ionospheric delay
• (4) Scan selectively double differenced phase
• Look for jumps
• Attribute each DD jump to 1 sat and 1 station
• (5) Iterate steps 1-4 to improve estimates
• Phase data set now bias flags at each possible slip and
after gaps
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How autcln works
(III)
• (6) Remove short segments
• (Actually, they are assigned a flag to “unweight” them.)
• (7) Estimate the number of cycles missing (jumped) at
each bias flag
• by polynomial fits to surrounding data
• use good data from other stations and satellites.
• determine integer values and their reliability
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How autcln works
(IV)
• (7) Iterate step 7 using previously-cleaned data
• (8) Estimate receiver and satellite clock offsets again
– use the phase data in an iterative process
– generate new one-way phase residuals
– (sum for each station and satellite is zero)
• (9) Write clean C-files
– preserve input C-files, OR
– over-write intermediate C-files
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autcln command file
• Go to your computer to examine the distributed
autcln.cmd file
– Note the use of the POST option
– Which options would you change for older codeless data?
• Using sh_gamit makes 2 summaries:
– autcln.cmd.prefit AND
– autcln.cmd.posfit
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Checking autcln.sum files
• Postfit scatter
– Usually RMS < 10 mm
• Discarded data
– Usually < 10% data discarded
– More than 20% discarded indicates problem
• Missed cycle slips are now very rare
– Most problematic slip is
• 1 cycle in L1 AND 1 cycle in L2
• does not change WL
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Why are ALL the data from
my favorite station deleted?
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This question is number 1 FAQ
Bias flags too close together
Post-fit phase RMS too large
Check editing reports in autcln.sum
Bad apriori coordinates
– Example
/dell3/tah/swis/gps00/1999_149/autcln.post.sum
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Autcln commands
• Read the $HELP_DIR/autcln.hlp file
• Also output by just typing autcln
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Tuning autcln
• dd_fit_tol
• sets the sizes of jumps to be flagged as
– ratio to rms
– min size
– max size
• ion_jump
• similar parameters for ionspheric jumps
• trim_oneway
• sets minimum sizes for segments of data as
– time
– number of epochs
– ratio to good length
– min at end
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Summary
• Default autcln.cmd usually works fine
• Tuning is useful for
– anomalous data
– some old data
• If you need to tune
– delete the link in the day dir -> tables dir
– copy the autcln.cmd file to the day dir
– modify the autcln.cmd file in the day dir
– re-run sh_gamit (or bexpt?.bat) for that day
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