NAME
cdpvel3d - 3D pre-stack binned cdp gathers
SYNOPSIS
cdpvel3d [ -Nntap ] [ -Ootap ] [ -vvtap ] [ -dmindstmin ] [
-dmaxdstmax ] [ -ddeldstmax ] [ -diminmindi ] [ -dimaxmaxdi
] [ -liminminli ] [ -limaxmaxli ] [ -x1x1 ] [ -y1y1 ] [
-x2x2 ] [ -y2y2 ] [ -x3x3 ] [ -y3y3 ] [ -x4x4 ] [ -y4y4 ] [
-cldmcldm ] [ -ildmildm ] [ -angmnangmin ] [ -angmxangmax ]
[ -R ] [ -V ] [ -? ]
DESCRIPTION
cdpvel3d for a given portion of a pre-stack survey takes the
input data and bins the traces into a model spread geometry
for each bin. To avoid the deleterious effects of moveout
variations within an offset bin a brute NMO correction is
done prior to stacking into the bins (and undone again
before the stacked result is put back as the current trace).
Optionally ranges of azimuths can be rejected allowing some
directional noise attenuation and some means to align the
gathers along, say, a dip or a strike line. This option
might also help in the 3D analysis of the effects of aniso-
tropy.
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 SrRcMX and
SrRcMY are optional since they can be calculated internally.
It is important to realize that this is not a stack - you
will get a whole gathers worth of data at each bin location.
Also the gathers will be output without NMO applied..
cdpvel3d gets both its data and its parameters from command
line arguments. These arguments specify the input, output,
a brute velocity, output survey extent, spread options,
azimuth limiting 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'.
-O otap
Enter the output cdp stack data set name or file
immediately after typing -O. This output file must be
a disk file and cannot be piped.
-v vtap
Enter the name of the RMS TDFN-format velocity disk
file.
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 (2-3 side) cell dimension (ft,m).
For most shooting geometries this will be 1/2 the group
or line spacing depending on the orientation of side
2-3 with respect to the receiver lines. No default.
-ildm ildm
Enter the inline (1-2 side) cell dimension (ft,m). For
most recording geometries this will be 1/2 the group or
line spacing depending on the orientation of side 1-2
with respect to the receiver lines. 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.
-angmx angmax
Enter maximum azimuth to reject (degr). If the minmum
and maximum reject angles ar e equal no azimuthal
rejection will be done. Default = 0
-angmn angmin
Enter minimum azimuth to reject (degr). If the minmum
and maximum reject angles ar e equal no azimuthal
rejection will be done. Default = 0
-R Enter the command line argument '-R' to restart a pre-
vious run that has stopped for some reason. The stderr
messages will announce every sequential record about to
be processed so the user can easily determine where in
the input data set the process stopped. By using suit-
able editt parameters the cdp run can be continued at
the point at which it stopped without the previous data
being wiped.
-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. cdp stack from disk input:
gather -N/data1/indat1 -N/data1/indat2 -N/data1/indat3 -S |
\
cdpvel3d -Ocdp -x13000 -y12000 -x20 -y23000 -x30 -y30
-x43000 -y40 \
-vvel_tdfn -ildm50 -cldm100 -dmin200 -dmax6800 -ddel200 \
-dimin28 -dimax48 -limax28 -dimax48 -angmn45 -angmx135
binstk -Ncdp -xf6800 -xd200 | \
rstak -Ogather_out -n441
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). The single brute velocity func-
tion is contained in the file vel_tdfn. We will take traces
that have azimuths between 45 and 135 degrees only. We also
run binstk to make sure the gathers al all properly binned
and that there are no duplicate trace distances. Then rstak
vertically sums all the binned gathers into a single super
gather (if you don't know how many cells there really are
for the rstak -n[] parameter just put in a large number - it
will stop at the end of the data).
2. cdp from tape input:
xcram10 -r | \
cdpvel3d -Ocdp -x13000 -y12000 -x20 -y23000 -x30 -y30
-x43000 -y40 \
-vvel_tdfn -ildm50 -cldm100 -dmin200 -dmax6800 -ddel200 \
-dimin28 -dimax48 -limax28 -dimax48 -shot
where the input here is from a tape stacker accessed using
xcram10.
SEE ALSO
sr3d1, sr3d2, cdpstk3d
AUTHOR
Paul Gutowski (socon 422) 3146
COPYRIGHT
copyright 2001, Amoco Production Company
All Rights Reserved
an affiliate of BP America Inc.
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