NAME
dmovel3d - true amplitude 3D pre-stack dmo CDP gathers
SYNOPSIS
dmovel3d [ -Nntap ] [ -Ootap ] [ -Tttap ] [ -vvtap ] [
-dmindstmin ] [ -dmaxdstmax ] [ -ddeldstmax ] [ -diminmindi
] [ -dimaxmaxdi ] [ -liminminli ] [ -limaxmaxli ] [ -x1x1 ]
[ -y1y1 ] [ -x2x2 ] [ -y2y2 ] [ -x3x3 ] [ -y3y3 ] [ -x4x4 ]
[ -y4y4 ] [ -cldmcldm ] [ -ildmildm ] [ -AS ] [ -CSA ] [
-COA ] [ -BKA ] [ -GS ] [ -R ] [ -shot ] [ -dipmangmax ] [
-V ] [ -? ]
DESCRIPTION
dmovel3d is a dmo implementation from the Colorado School of
Mines Center for Wave Phenomena. It is basically a born-
type algorithm that takes input data in any form (shot, cdp,
etc), an RMS velocity field, and outputs a zero offset true
amplitude gathers for each output bin. The spread will be
defined by the user.
As each input trace is read in the amplitudes are corrected
for the type of spreading desired and then sprayed out along
the dmo ellipse accumulating in the proper CMP bin locations
in time in the output spread array in each bin. Optional
correction can be made for the number of live samples in the
accumulating sums. Unlike some dmo codes no prior NMO
correction is applied; this is all done internally (which is
why we need the RMS velocity field).
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.
For data in shot order it is assumed that all basic correc-
tions have been made, e.g. refraction statics, velocity
analysis, residual statics. Other processes such as deconvo-
lution and filtering can be done on the fly before input
into the DMO.
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 with NMO applied. To input
these data into velocity analysis codes you must run reverse
NMO.
dmovel3d gets both its data and its parameters from command
line arguments. These arguments specify the input, output,
the dmo velocity, output survey extent, spread options,
wavefield spreading 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 dmo stack data set name or file
immediately after typing -O. This output file must be
a disk file and cannot be piped.
-T ttap
Normalization file name. This must be a disk file and
will be the same size as the -O[] output file. Basi-
cally each time of each output trace must be normalized
by the number of live samples.
-v vtap
Enter the name of the the USP format velocity disk
file. There must be a velocity trace for every output
cell of the survey. Unlike some DMO codes this code
allows a different velocity function at each cell.
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 line
or group 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 line or
group 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.
-dipm dipm
Enter maximum dip (degrees) to process. Default = 90.
-AS If present on the command line turn off the anti alias
constraints and process all dips.
-CSA If present on the command line apply common shot ampli-
tude term. This is also the default. Note: either this
option or the common offset option below both preserve
amplitudes well; use of the kinematic term will not be
so nice to the amplitudes but the code will run some-
what faster.
-COA If present on the command line apply common offset
amplitude term.
-BKA If present on the command line apply Kirchhoff
kinematic amplitude term.
-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 DMO run can be continued at
the point at which it stopped without the previous data
being wiped.
-GS If present on the command line use geometric spread,
otherwise zero offset spreading will be used.
-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. DMO stack from disk input:
gather -N/data1/indat1 -N/data1/indat2 -N/data1/indat3 -S |
\
dmovel3d -Odmo -x13000 -y12000 -x20 -y23000 -x30 -y30
-x43000 -y40 \
-vvel_tdfn -ildm50 -cldm100 -dmin200 -dmax6800 -ddel200
\
-dimin28 -dimax48 -limax28 -dimax48 -shot
binstk -Ndmo -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). 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. DMO from tape input:
xcram10 -r | \
dmovel3d -Odmo -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, dmostk3d
AUTHOR
Paul Gutowski using DMO amplitude formulation due to Chris
Liner, formerly Colorado School of Mines
COPYRIGHT
copyright 2001, Amoco Production Company
All Rights Reserved
an affiliate of BP America Inc.
Man(1) output converted with
man2html