NAME
fxpwmig - Prestack Common Angle v(x,z) Depth Migration
SYNOPSIS
fxpwmig -Npwtime -Opwdepth -VELveltape -DXTdxt -DZTdzt \
-fxpwmig.crd"\
TIME ENDTIMEMS PADTIMEMS BEGTIMEMS DTMS TMUTE
TIME endtime padtime begtime dtms tmute
FREQUENCY MINFREQHZ F2FREQHZ F3FREQHZ MAXFREQHZ
FREQUENCY f1 f2 f3 f4
DEPTH MAX DEPTH DELTA Z
DEPTH zmax dz
WIDTH DELTAX BEG REC END REC REC INC BEGTRACE ENDTRACE
WIDTH dx irbeg irend irinc itrbeg itrend
MODEL REF VELOC BEAMWIDTH STARTX IXTAPER
MODEL vref beamwidth startx ixtaper
IMAGE NATOP NABOT STRETCHX
IMAGE natop nabot stretchx
# ANGLES START INCREMENT
nang start anginc
"
#...|....1....|....2....|....3....|....4....|....5....|....6....|....7
STARTJOB
Create a file that looks like the above synopsis with the
following command:
catpat fxpwmig > fxpwmig.job
This job file, fxpwmig.job, will have some suggested param-
eter values entered. Edit the file to suit your needs and
submit fxpwmig.job with the following command:
startjob fxpwmig.job
DESCRIPTION
fxpwmig performs a V(x,z) prestack depth migration using an
FX algorithm. The inputs are a set of constant angle time
sections from a USP compatible dataset, a USP-formatted
velocity field, parameters read from the embedded menu cards
shown above, and the following command line arguments. This
prestack migration is the most accurate of all of the migra-
tion codes and and can handle rapid lateral and vertical
velocity changes. But it is also the most expensive pres-
tack program to run and therefore should primarily be used
as a final migration.
Command line arguments
-N pwtime
Enter the name of constant angle input time sections
after typing -N. This dataset should have been created
by the series of programs: splitss, presort, unsr,
slnt, and memangs (or angs). Programs presort and unsr
are usp programs for unsorting to shots (or receivers).
Programs splitss, slnt, and memangs (angs) are mbs pro-
grams which synthesize split spreads in the cdp domain,
slant stack common source (or receiver) data and sort
to the common angle domain.
-O pwdepth
Enter the dataset name of the output constant angle
depth sections after typing -O.
-VEL veltape
This is a USP-formatted dataset where sample values are
interval velocities.
-DXT dxt
Enter input velocity dataset trace spacing (ft or
meters) after typing -DXT. Default is velocity dataset
line header value (Dx1000/1000). This must be speci-
fied if the velocity dataset originated from anywhere
other than "mbs" programs.
-DZT dzt
Enter input velocity dataset depth spacing (ft or
meters) after typing -DZT. Default is velocity dataset
line header value (Dz1000/1000). This must be speci-
fied if the velocity dataset originated from anywhere
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.
-fxpwmig.crd"\
This keyword, -fxpwmig.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.
Description of Parameters
ENDTIMEMS endtime
Enter the end time in ms. This value should be <= the
maximum time on input. Default is maximum time on
input.
PADTIMEMS padtime
This value is in ms. It is used for zero padding
traces to reduce frequency wrap around. If the
requested maximum depth exceeds the computed maximum
depth (computed from maximum time and velocity struc-
ture), the migrated seismic data will wrap around.
This will cause repeats of the shallower seismic data
at those depths which are undefined by the data.
Default is 0.
BEGTIMEMS begtime
Enter the beginning time in ms. This is used mainly for
model data.
Enter the input sample spacing in ms. Default is line header
value.
TMUTE mute
Enter the onset time of the first arrival mute in ms.
MINFREQHZ F2FREQHZ F3FREQHZ MAXFREQHZ f1 f2 f3 f4
Enter the points in the trapezoidal filter (in Hz).
MAX DEPTH zmax
Enter the maximum depth (ft or meters) to which to
migrate. No default.
Enter the depth sample spacing in ft or meters.
This should be <= vmin/(maxfreq*4). No default.
Trace spacing in ft or meters. No default.
BEG REC irbeg
The beginning record of the input to process. Default
is 1.
END REC irend
The last record of the input to process. Default is
the number of records specified in the input line
header.
REC INC irinc
The record increment. Default is 1.
BEGTRACE itrbeg
Beginning trace to process. Default is 1.
ENDTRACE itrend
Ending trace to process. Default is the number of
traces per record.
REF VELOC vref
Reference velocity (in ft/sec or m/sec) of the dip
filter.
BEAMWIDTH beamwidth
The reflected field is dip filtered around the normal
incidence ray where the angular pass zone is
"beamwidth" wide (in degrees). If beamwidth is near 0,
only normal incidence data will be passed. Reflections
from flat layers with emergent angles greater than
2*beamwidth will be attenuated.
RTX startx
Enter the location (in ft or meters) of the first input
trace relative to the model. This can be a negative
number, in which case the model will be extended.
IXTAPER ixtaper
Enter number of live traces to taper at side boundaries
to reduce edge effects.
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! Default
value = 1.0.
#ANGLES nang
Enter the number of angles on the input dataset. Must
match input.
RT start
Enter the starting angle (in degrees) on the input
dataset. Must match input.
INCREMENT anginc
Enter the angle increment (in degrees) on the input
dataset. Must match input.
SEE ALSO
mbs, startjob, beginjob, endjob, pwmvzn, kmpw, ellippw
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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