NAME
disort - sort, range limit, fix trace order according to
trace distances, bin
SYNOPSIS
disort [ -Nntap ] [ -Ootap ] [ -ntrntr ] [ -hwhdrwrd ] [
-dmindmin ] [ -dmaxdmax ] [ -xnofffar ] [ -xddx ] [ -S ] [
-M ] [ -neg ] [ -nint ] [ -I ] [ -P ] [ -D ] [ -R ] [ -X ] [
-V ] [ -? ]
DESCRIPTION
disort puts dead traces in their proper order, range limits,
interpolate traces into model spread. The user inputs some
information concerning the spread geometry which disort uses
to build a model. The user may specify that the current
trace distances be binned according to the spread model with
a simple trace rearrangement but may also specify the option
to interpolate traces according to the old versus the new
binned distances. The live traces distances are then fit to
this model and the dead traces are interspersed in the
remaining slots.
Using the model spread option may result in more traces/rec
on output unless no padding is specified. The number of
traces will be equal to the number of channels in the model
spread. If no padding is specified then input groups could
be lost off the ends of the spread if the input trace spac-
ing results in too many dead traces being interspersed.
In the modeling option the group interval should be the
correct one or unpredictable results can occur. The far
offset need only be large enough to span the maximum far
offset in the data or to span the range of offsets the user
is interestedin.
This program is ideal for fixing up data coming from pro-
grams such as sisort and memsrt in USP, data coming from
DISCO or PROMAX, or land data with funky trace distances.
disort also sorts traces by distance (either ascending or
descending) on a record-by-record basis; distance limits
also
Command line arguments
-N ntap
Enter the input data set name or file immediately after
typing -N. This input file should include the complete
path name if the file resides in a different directory.
Example -n/vsp/dummy tells the program to look for file
'dummy' in directory 'vsp'.
-O otap
Enter the output data set name or file immediately
after typing -O. If the output is to be piped no -O
entry should be given. The output data set also
requires the full path name (see above).
-hw hdrwrd
If simple trace rearrangement is requested, i.e. no
model spread options, the trace ordering can be based
on any trace header word, The default is DstSgn, signed
trace distance.
-ntr ntr
If nopad is specified (see below) enter the output
number of traces per record passed within the limits
specified by the -dmin or -dmax entries. This must be
entered correctly if either of the range limit parame-
ters are given or the nopad flag is given
-dmin, -dmax dmin, dmax
Enter the range limits. Depending on the presence of
the flag -P this will cause ranges to be passed within
the limits or passed outside the limits (always includ-
ing the limits themselves, if the exist). Note: these
are turned off when the model option is selected below.
-xd dx
Enter the trace spacing of the gathers (ft,m). If this
entry is not on the command line disort will only fuc-
tion in its distance limitting mode and will not alter
the trace order.
-xn offfar
Enter the absolute maximum far offset (ft,m).
-S Enter the command line argument '-S' to specify a split
spread. In this case the near offset and trace spacing
should define the positive side of the spread only.
-M Enter the command line argument '-M' to model the
spread according to the spread model generated from the
maximum offset and the actual group spacing of the
data. The binning operation is a simple rearrangement
of the traces (see the interpolation option below).
-nint
Enter the command line argument '-nint' cause the
regridding of the input trace distances to be nearest
integers instead of just integers, i.e. the input dis-
tances are divided by the dx value to determine where
along the model spread the trace really belongs. This
pointer can either be calculated by throwing away the
fractional part (default) or going to the nearest
integer (nint). Sometimes going to nearest integer
gives a better distribution of interspersed dead
traces.
-neg Enter the command line argument '-neg' to specify the
input trace distances are a single ender with negative
trace distances; otherwise the single ender is assumed
to be positive.
-I If the bin mode above has been selected include '-I' on
command line if the traces are to be interpolated from
the old tarce distances to the new binned distances.
You might wish to do this for shot data. It might not
make sense to do this for CDP data since there may be
large gaps between some of the bins especially in the
case of land data. The interpolation uses a cubic
spline algorithm (the same one used in spacetrp).
-P Enter the command line argument '-P' to pass traces
having distances within or equal to dmin and dmax, oth-
erwise the rule is that traces having distances less
than or equal to dmin or distances greater than or
equal to dmax will be passed. Note: this has no effect
if the model option is chosen.
-D Enter the command line argument '-D' for distance lim-
iting (pass or reject) by flagging the traces to be
rejected as dead traces. Note that this does not actu-
ally remove these traces from the gather but hides them
from processing. They can later be unflagged.
-R Enter the command line argument '-R' to sort traces in
descending order instead of the default ascending
order.
-X For the dmin/dmax options: Enter the command line
argument '-X' to cause the output records to not be
padded with dead traces to make up for traces filtered
out by the dmin, dmax entries. Unless the model option
is selected choosing -X means you must know in advance
how many traces will be output from the filtering
operation (which must specified with the -ntr entry)
and of course the data must be completely regular with
each record having a complete set of distances. For the
model spread options: If the model option is chosen
the output number of traces will be determined by the
number of bins in the spread model.
-V Enter the command line argument '-V' to get additional
printout.
-? Enter the command line argument '-?' to get online
help. The program terminates after the help screen is
printed.
BUGS
For the model option is important to input the correct group
spacing. Failure to do so can cause upredictable results to
occur.
EXAMPLES
(1) distance selector
sisort -Nindata -nsortable -D -l20 -m50 |
disort -Outdata -dmin-500 -dmax500
Here cdp's 20 through 50 are taken from the original PI data
indata (presort was run first, of course, to build the sort
table sortable) and fed into disort where the traces within
each cdp are sorted by distance in ascending order and the
cdp records output to disk file outdata. The inside traces
are rejected (no -P on command line)
Note: the output records of disort will be padded with dead
traces to fill out the original record size
(2) fix up trace ordering
sisort -Nindata -nsortable -D -l20 -m50 |
disort -Outdata -xn500 -xd100 -M
This is the same sisort as in the pervious example. disort
builds a model in which the gather is assumed to have a near
offset of 500 and a trace spacing of 100 (the actual gathers
coming out of sisort in this case happen to have 10 traces
so that the far offset will the be 1400). The live traces
are arranged according to their distances in their proper
model slots. Any dead traces are put into the remaining
slots after fixing their header information.
COPYRIGHT
copyright 2001, Amoco Production Company
All Rights Reserved
an affiliate of BP America Inc.
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