NAME
predecon3d - 3D surface consistent (time varying) decon:
first pass - compute autocorrelations
SYNOPSIS
predecon3d [ -Nntap ] [ -SHOTstap ] [ -GRUPrtap ] [ -XOFFx-
tap ] [ -dmindstmin ] [ -dmaxdstmax ] [ -ddeldstmax ] [
-diminmindi ] [ -dimaxmaxdi ] [ -liminminli ] [ -limaxmaxli
] [ -x1x1 ] [ -y1y1 ] [ -x2x2 ] [ -y2y2 ] [ -x3x3 ] [ -y3y3
] [ -x4x4 ] [ -y4y4 ] [ -cldmcldm ] [ -ildmildm ] [ -ppr ] [
-olol ] [ -Pprew ] [ -wsist ] [ -weied ] [ -wvvel ] [ -TV ]
[ -wwind ] [ -R ] [ -V ] [ -? ]
DESCRIPTION
predecon3d builds surface consistent autocorrelations
required by the predictive deconvolution and stores these on
disk. Each input trace has a source cell, a receiver cell,
and an offset bin associated with it. The autocorrelation
and the correlation of the input with the desired output are
computed and stored in one vector. This correlation vector
is then summed into whatever is in the current shot cell,
receiver cell, and offset bin (if they lie within the
desired limits of the survey). The number of "hits" on each
cell for shot, receiver, and offset are kept track of. Also
the normalization for each trace is kept track of in a simi-
lar manner. All this information ends up in the three disk
files (shot, receiver, and offset). The files are then read
through, cell by cell, the autocorrelations are normalized
by the number of "hits" in each cell. When all the auto-
correlations have been computed and stored they can be read
by decon3d which is the second pass and which does the
actual filter computation and application.
The autocorrelations (and hence the resulting filters) may
be computed in time varying mode for a sliding window down
the traces. In this case the window is moved down by 1/2 the
window length at a time resulting in nwin discrete window
positions. The nwin autocorrelations for each cell are
stored in a single trace and unpacked by decon3d and the
resulting filters computed and applied.
The input data can be in any sort order (shot, group, cdp,
offset) but must at least have the source X-Ys (SrPtXC and
SrPtYC) and the receiver X-Ys (RcPtXC and RcPtYC) trace
header words properly filled in since these are are critical
to calculating where the trace belongs. The output data con-
sists of the three decon filter files for shot, receiver,
and offset.
It is strongly recommended that a brute NMO followed by a
mute be applied to the data prior to both predecon3d and
it's application follow-on decon3d. The moveout can be
unapplied to the data output from the application step. The
reason for this is even a brute NMO tends to minimize offset
variations of the multiple periods making the above type of
operator computation much more robust.
predecon3d gets both its data and its parameters from com-
mand line arguments. These arguments specify the input,
output, decon parameters, output survey extent, spread
options, and verbose printout, if desired.
Command line arguments
-N ntap
Enter the input data set name or file immediately after
typing -N unless the input is from a pipe in which case
the -N entry must be omitted. This input file should
include the complete path name if the file resides in a
different directory. Example -N/b/vsp/dummy tells the
program to look for file 'dummy' in directory '/b/vsp'.
-SHOT stap
Enter the output autocorrelation disk file associated
with shots. The size of this file will be equal to the
product of the number of cells in the survey times
twice the operator length. This output cannot be piped.
No default. This output file must be a disk file and
cannot be piped.
-GRUP rtap
Enter the output autocorrelation disk file associated
with groups. The size of this file will be equal to the
product of the number of cells in the survey times
twice the operator length. This output cannot be piped.
No default.
-XOFF xtap
Enter the output autocorrelation disk file associated
with offsets. The size of this file will be equal to
the product of the number of bins in the spread times
twice the operator length. This output cannot be piped.
No default. This output file must be a disk file and
cannot be piped.
x4, y4]
-x1, -y1, -x2, -y2, -x3, -y3, -x4, -
y4 [x1, y1, x2, y2, x3, y3,
Enter the area of interest over the survey with the X-Y
coordinates (ft,m) defining the four corners of a
parallelogram on the ground. Going either clockwise or
counter clockwise (clockwise recommended) from Corner 1
the first move to Corner 2 should be in the direction
of a receiver or shot line. The direction 1-2 will
always define the Y or DI direction. The DIs will
always start from side 1-4 and increase in the 1-2 (Y)
direction; the LIs will always start from side 1-2 and
increase in the 1-4 (X) direction. The values must be
the same units as those given in the source, receiver,
and midpoint X-Ys in the trace headers.
-cldm cldm
Enter the crossline (along X or side 2-3) cell dimen-
sion (ft,m). For most shooting geometries this will be
1/2 the line or group spacing depending on the orienta-
tion of side 2-3 with respect to the receiver lines.
The sides are defined to be X along side 1-4 (roughly
cross-line direction), Y along side 1-2 (roughly in-
line direction). Remember when setting up the coordi-
nate system the line joining Corner (1) to Corner (2)
should be in the direction of a receiver or shot line.
No default.
-ildm ildm
Enter the inline (along Y or side 1-2) cell dimension
(ft,m). For most recording geometries this will be 1/2
the line or group spacing depending on the orientation
of side 1-2 with respect to the receiver lines. The
sides are defined to be X along side 1-4 (roughly
cross-line direction), Y along side 1-2 (roughly in-
line direction). Remember when setting up the coordi-
nate system the line joining Corner (1) to Corner (2)
should be in the direction of a receiver or shot line.
No default.
-dmin dstmin
Enter the minimum offset to use in the output spread
(in ft,m). The number of gathers is computed by
(dstmax-dstmin)/ddel + 1. No default.
-dmax dstmax
Enter the maximum offset to use in the output (in
ft,m). No default.
-ddel dstdel
Enter the output spread group interval (in ft,m). No
default.
-limin, limax minli, maxli
Enter the minimum and maximum line indexes to output.
The output survey will have so many bins in the inline
direction and so many bins in the crossline direction.
This is a must set of parameters to limit the region of
interest for velocity analysis. Default is the first
and last inline bin as determined from the 4 corners of
the survey provided on the command line. But beware if
you default these parameters you need the appropriate
disk space for (limax-limin+1) * (dimax-dimin+1) *
(number groups in spread) traces.
-dimin, dimax mindi, maxdi
Enter the minimum and maximum crossline indexes to out-
put. The output survey will have so many bins in the
inline direction and so many bins in the crossline
direction. his is a must set of parameters to limit the
region of interest for velocity analysis.
-p pr
Enter the prediction distance (ms). Default = spiking.
-ol ol
Enter the operator length (ms). Recall from decon
theory that the result of predictive decon on the auto-
correlation will be to zero it from the prediction dis-
tance out to the operator length leaving the remainder
untouched. No default.
-P prew
Enter % prewhitening. This has the effect of limiting
the deconvolution spectrally as it is increased to the
larger amplitudes. Small amounts of prewhitening are
necessary to prevent the solution of the normal equa-
tions from blowing up. Default =.01
-ws ist
Enter the design window start time (ms). Samples above
this time will not take part in the design of the decon
operator. Default is the start of the trace. This will
have no meaning if using the time varying option.
-we ied
Enter the design window end time (ms). Samples below
this time will not take part in the design of the decon
operator. Default is the end of the trace. This will
have no meaning if using the time varying option.
-wv vel
Enter the design window velocity. This will cause the
window start time to move out according to the relation
ist + dist/vel, where dist is the trace distance.
Default = no moveout. This will have no meaning if
using the time varying option.
-TV Enter the command line argument '-TV' to use the time
varying decon option (you will need to input the length
of the sliding window) also.
-w wind
Enter the length (ms) of the sliding design/application
window. This window is slid down the trace 1/2 the win-
dow length at a time. The autocorrelation and subse-
quent filter application are done independently at each
window position. The resulting nwin decon filters are
stored in a single trace.
-shot
Enter the command line argument '-shot' to tell the
program shot data is being input. Currently this option
does nothing.
-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
No checks on the input trace headers to see if they have
valid source, receiver, or midpoint X-Ys.
EXAMPLE
1. pre-stack decon (first pass) from disk input:
gather -N/data1/indat1 -N/data1/indat2 -N/data1/indat3 -S |
\
predecon3d -SHOTsht -GRUPgrp -XOFFoff -x13000 -y12000 -x20
-y23000 -x30 -y30 -x43000 -y40 \
-ildm50 -cldm100 -dmin200 -dmax6800 -ddel200 -p32 -ol200 \
-dimin28 -dimax48 -limax28 -dimax48
where the the X-axis corresponds to the receiver lines and
we go counter clockwise starting from the upper right
(northeast) corner along a receiver line. The input data is
spread out over 3 disk partitions and we use gather to
assemble them in sequence. The area of interest has been
restricted to DIs between 28 and 48 and LIs between 28 and
48 (a total of 441 cells). A prediction distance of 32ms and
an operator length of 200ms has been used.
2. pre-stack decon (first pass) from tape input:
xcram10 -r | \
predecon3d -SHOTsht -GRUPgrp -XOFFoff -x13000 -y12000 -x20
-y23000 -x30 -y30 -x43000 -y40 \
-vvel_tdfn -ildm50 -cldm100 -dmin200 -dmax6800 -ddel200
-p32 -ol200 \
-dimin28 -dimax48 -limax28 -dimax48 -shot -TV -p32 -ol200
-w500
where the input here is from a tape stacker accessed using
xcram10. A prediction distance of 32ms and an operator
length of 200ms has been used in time varying mode where the
sliding design window is 500ms.
SEE ALSO
decon3d
AUTHOR
Paul Gutowski (socon 422) 3146
COPYRIGHT
copyright 2001, Amoco Production Company
All Rights Reserved
an affiliate of BP America Inc.
Man(1) output converted with
man2html