NAME
fxcmmig - Poststack Common Midpoint Migration V(x,z)
SYNOPSIS
fxcmmig -Ncdptime -Ocdpdepth -VELveltape -DXTdxt -DZTdzt \
-fxcmmig.crd"\
TIME ENDTIMEMS PADTIMEMS BEGTIMEMS DTMS
TIME endtime padtime begtime dtms
FREQUENCY MINFREQHZ F2FREQHZ F3FREQHZ MAXFREQHZ
FREQUENCY f1 f2 f3 f4
DEPTH MAX DEPTH DELTA Z
DEPTH zmax dz
WIDTH DELTAX BEGTRACE NOTRACE
WIDTH dx ibegtr inotr
MODEL REF VELOC DIP MAX STARTX IXTAPER
MODEL vref dip max startx ixtaper
IMAGE NATOP NABOT STRETCHX
IMAGE natop nabot stretchx
"
#...|....1....|....2....|....3....|....4....|....5....|....6
STARTJOB
Create a file that looks like the above synopsis with the
following command:
catpat fxcmmig > fxcmmig.job
This fxcmmig.job file will have some suggested parameter
values entered. Edit this file to suit your needs and sub-
mit fxcmmig.job with the following command:
startjob fxcmmig.job
DESCRIPTION
fxcmmig performs a V(x,z) poststack depth migration using an
FX algorithm. The inputs are a "normal incidence time sec-
tion", velocity field, and parameters from command line
arguments and the embedded menu. The "normal incidence time
section" is typically a CMP stack, but could be a (NMO
corrected) single offset section or a backscatter stack (see
bsstk).
Command line arguments
-N cdptime
Enter the input dataset name of the normal incidence
time section after typing -N.
-O cdpdepth
Enter the output dataset name of the migrated depth
section after typing -O.
-VEL veltape
Enter the name of the input interval velocity dataset
after typing -VEL. This must be a single record USP-
formatted dataset. It's starting trace should
correspond to the input time sections 1st trace -
except when modified by STARTX below. However, it is
generally advisable to have the velocity data and the
time data have the same starting trace. If you wish to
pad or change the size of your velocity data see pro-
grams vtrsiz and vtpad.
-DXT dxt
Enter the input velocity dataset trace spacing (feet or
meters) after typing -DXT. Default is velocity tape
line header value (Dx1000/1000). This must be speci-
fied if the velocity dataset originated from programs
other than "mbs" programs.
-DZT dzt
Enter input velocity tape depth spacing (feet or
meters) after typing -DZT. Default is velocity tape
line header value (Dz1000/1000). This must be speci-
fied if the velocity tape originated from programs
other than "mbs" programs.
-V Enter -V for a verbose printout.
-h Enter -h for online help. Program will terminate after
printing this.
-? Enter this (or '-?' if you are running in c-shell) to
get online help. The program will terminate after
printing this.
-fxcmmig.crd"\
This keyword, -fxcmmig.crd"\, must be entered exactly
as shown with no spaces after the backslash. The
embedded menu cards that follow this keyword must be
typed exactly as shown, with the lower case parameter
names being changed to the actual values you want the
program to use. All of the parameter values must be
entered in the correct columns. The double quote fol-
lowing the embedded menu cards must be present as
shown. (Note: catpat fxcmmig > junk will create a tem-
plate of these cards in a file called junk.)
Description of Parameters
ENDTIMEMS endtime
This value should be <= time on input data. Default
from input line header.
PADTIMEMS padtime
This value (in ms) is for zero padding traces to reduce
frequency wrap around. If the requested maximum depth
exceeds the computed maximum depth (computed from max-
imum time and velocity structure), the migrated seismic
data will wrap around. This will cause repeats of the
shallower seismic data at those depths which are unde-
fined by the data. The default is zero.
BEGTIMEMS begtime
Beginning time to migrate in ms. Used mainly for model
data.
Sample spacing in ms. Default is line header value.
MINFREQHZ F2FREQHZ F3FREQHZ MAXFREQHZ f1 f2 f3 f4
The points in the trapezoidal filter. Doubling of the
value of f4 quadruples the program run time.
MAX DEPTH zmax
This is the maximum depth (in ft or meters) to migrate.
No default.
This is the output depth sample spacing in ft or meters.
It should be <= vmin/(f4*4). No default.
This is the trace spacing (ft or meters) for the input dataset.
No default.
BEGTRACE ibegtr
The beginning trace number to use from the input as
count from the beginning. Default = 1.
RACE inotr
Number of consecutive traces to use from the input,
starting with the beginning trace ( ibegtr ). A single
output record will be produced. The input data can be
any breakdown of traces per record. No default.
REF VELOC vref
Reference velocity (in ft/sec or m/sec) for dip filter.
Normally this is the minimum velocity on the velocity
field.
Maximum dip (in degrees) to pass for the reference velocity.
A max dip of 90 will pass all physical dips if the
reference velocity < maximum velocity.
RTX startx
Location (in ft or meters) of the first input trace
relative to the model. The model lead in will be pad-
ded if startx < 0. Default = 0.
IXTAPER ixtaper
The number of traces to taper at side boundaries to
decrease edge effects. Recommended value = 5.
OP NABOT natop nabot
Parameters natop and nabot are entered as "number of
traces" and provide the program with the information
needed to determine the aperture of migration. The fx
algorithm extrapolates the f-x wavefield over small
(~10 meter) depth steps, and therefore requires a rela-
tively small half-aperture. Half aperture is computed
as NA, where NA = NATOP + (Z/ZMAX) * (NABOT-NATOP).
Typical ranges for NATOP are 20-30 and NABOT are 30-40.
Increasing the aperture size improves imaging (steep
dips and less numerical noise), but increases cost.
ETCHX stretchx
Horizontal regridding rate. The migration will be done
at "stretchx * dx" and then interpolated back to dx.
This decreases run time by the an amount equal to
"stretchx". Warning: watch spatial aliasing! Recom-
mended value = 1.0
SEE ALSO
mbs, startjob, beginjob, endjob, kmcm, cmmvzn, ellipmig
BUGS
None known.
AUTHOR
N. D. Whitmore, Jr.
COPYRIGHT
copyright 2001, Amoco Production Company
All Rights Reserved
an affiliate of BP America Inc.
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