NAME
dmovz - common offset (nmo-corrected) depth variable-v(t)-
dmo
SYNOPSIS
dmovz [ -Nntap ] [ -Ootap ] [ -cdpmincdpmin ] [
-cdpmaxcdpmax ] [ -dxcdpdxcdp ] [ -noffmixnoffmix ] [
-tdmotdmo ] [ -vdmovdmo ] [ -fmaxfmax ] [ -smutesmute ] [
-speedspeed ] [ -V ] [ -? ]
DESCRIPTION
dmovz is a common offset dip moveout code that uses an input
time-interval velocity function to do a depth variable dmo
operation. This is an exact method of handling vertical
velocity variations which makes no assumptions about the
offset, dip, or hyperbolic moveout. Even for a linear
increase in velocity with depth the dmo operator is multi-
valued and instead of the classic dmo ellipse the operator
has multiple branches.
The input data to dmovz is NMO-corrected common offsets.
The cost in run time is of course significantly higher than
for other single velocity methods but in data cases with
large vertical velocity changes this might be an appropriate
tool, particularly when combined with post-stack migration
(since the combination of v(z) dmo followed by post-stack
migration might be cheaper than fullblown pre-stack migra-
tion).
dmovz gets both its data and its parameters from command
line arguments. These arguments specify the input, output,
the cdp window, the cdp interval, the start and end traces,
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 data set name or file immediately
after typing -O. This output file is not required when
piping the output to another process. The output data
set also requires the full path name (see above).
-cdpmin cdpmin
Enter the minimum cdp number (integer) to apply dmo
operation. This should be equal to or less than the
smallest CDP number in the data set. Making it much
less than the smallest CDP number will cause no prob-
lems with the dmo but the program will require more
memory than it really needs. No default. You can always
run presort on your data and look at the top of the
table (3rd column of primary sort indexes and the bot-
tom of the table for the minimum and maximum cdp
numbers respectively.
-cdpmax cdpmax
Enter the maximum cdp number (integer) to apply dmo
operation. This should be equal to or greater than the
largest CDP number in the data set. Making it much
greater than the largest CDP number will cause no prob-
lems with the dmo but the program will require more
memory than it really needs. No default.
-dxcdp dxcdp
Enter the distance between adjacent cdp bins (ft, m).
No default
-noffmix noffmix
Enter the number of offsets to mix. The number of
offsets to mix (noffmix) should typically equal the
ratio of the shotpoint spacing to the cdp spacing.
This choice ensures that every cdp will be represented
in each offset mix. Traces in each mix will contribute
through DMO to other traces in adjacent cdps within
that mix. No default.
-tdmo, -vdmo ["tdmo,tdmo,..."] ["vdmo,vdmo,..."]
Enter (optional) the time interval velocity pairs on
the command line. After the command line key (-tdmo or
-vdmo) input all the corresponding values each
separated by a comma and eclosed by double quotes, e.g.
-tdmo"0,1000,2000,4000" -vdmo"1500,2000,3500,4000" ...
-fmax fmax
Enter the maximum frequency to process (hz). Default =
Nyquist
-smute smute
Enter the stretch mute used for dmo correction. The
larger the value the less the muting. This establishes
a minimum time to calculate the dmo operator and is
dependent on the offset, the cdp spacing, and the shal-
lowest velocities. It's a very good idea to run a sin-
gle offset through a test suite to see how large you
need to make this parameter. Default = 1.5
-speed speed
Twist this knob for speed (and aliasing). Increasing
this parameter makes the ray parameter sampling coarser
which will make the code run faster but leave you open
to the effects of aliasing. For most real data cases
looked at so far 2.0 seems to be a good compromise
between speed and aliasing. This value will result in
a 50% decrease in run time. Default = 1.0
-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
Unkown at present
SEE ALSO
dmofast, dmofx, dmoamp
EXAMPLE
Suppose the input data is shots.raw, then we first run a
presort to build our sort table to get us into the offset
domain.
presort -Nshots.raw -Oshot.tbl
sisort -Nshots.raw -nshot.tbl -X |
dmovz -dxcdp75 -cdpmin124 -cdpmax537 -noffmix1
-tdmo"0,800,1600,2400,3224"
-vdmo"6011,6759,10280,13440,16030"
-fmax50 -smute2.0 -Ooffset.dmovz
where CDP spacing is 75, the minimum and maximum CDP indexes
are 124 and 537 respectively, the number of offsets to mix
together is 1, and the maximum frequency is 50. The velo-
city function is interval-time. The speed factor has been
raised slightly over the default.
Next we run another presort on the file offset.dmovz so that
the next sisort will get back to shot, receiver, of CDP
domains.
presort -Noffset.dmovz -Ooffset.tbl
sisort -Noffset.dmovz -noffset.tbl -D -Ocdps
AUTHOR
Original code by Craig Artley, Colorado School of Mines
Center for Wave Phenomena; USP version originally by Joe
Wade (with Paul Gutowski kibbitzing)
COPYRIGHT
copyright 2001, Amoco Production Company
All Rights Reserved
an affiliate of BP America Inc.
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