NAME
kmpw - Kirchhoff Constant Angle Prestack Depth Migration
SYNOPSIS
kmpw -Npwtime -Opwdepth -VELveltape -Sstretchparm -DXTdxt -DZTdzt \
-kmpw.crd"\
TIME ENDTIMEMS PADTIME BEGTIMEMS DTMS TMUTE
TIME endtime padtime begtime dtms mute
FREQUENCY MINFREQHZ F2FREQHZ F3FREQHZ MAXFREQHZ
FREQUENCY f1 f2 f3 f4
DEPTH MAX DEPTH DELTA Z 1ST DEPTH 2ND DEPTH
DEPTH zmax dz dep1 dep2
WIDTH DELTAX BEG REC END REC REC INC BEGTRACE ENDTRACE
WIDTH dx irbeg irend irinc itrbeg itrend
MODEL REF VELOC EMERG ANG DIPMAX
MODEL vref emerg dipmax
IMAGE MIG 1/2 AP DZMIG NRAYINC ISMOOTH ISTRIDE
IMAGE nap dzmig nrayinc ismooth istride
# ANGLES START INCREMENT
numang start inc
"
#...|....1....|....2....|....3....|....4....|....5....|....6....|....7
STARTJOB
Create a file that looks like the above synopsis with the
following command:
catpat kmpw > kmpw.job
This kmpw.job file will have some default parameter values
entered. Edit this file to suit your needs and submit
kmpw.job with the following command:
startjob kmpw.job
DESCRIPTION
kmpw performs a V(x,z) plane wave prestack depth migration
on a suite of common angle records. For each record, the
data is imaged by summing the effects of each trace on all
subsurface points (x,z) at times T = TP(x,z) +
TR(x0,z0,x,z), where TP(x,z) is the time for the energy from
a plane wave source to arrive at the point (x,z), and
TR(x0,z0,x,z) is the time for the scattered energy to return
to the surface. The traveltimes, TP and TR are determined
by ray tracing. Only the contributions within a specified
migration aperture centered around each trace (located at
x0) are computed. The inputs are a set of constant angle
time sections and a velocity field, both of which are USP
compatible datasets. Parameters are read from the embedded
menu cards shown above, and command line arguments described
below.
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 output name of constant angle migrated depth
sections after typing -O.
-VEL veltape
Enter the input velocity dataset name after typing
-VEL. This is a USP-formatted dataset where sample
values are interval velocities. The spatial origin of
this velocity field must match the input time data!
-S stretchparm
This parameter is multiplied times each velocity value,
the depth increment, and the maxdepth. This can be
used to make a constant change to all the velocity
values without regenerating a velocity dataset. Note
this changes the output depth spacing. Default and most
typical = 1.
-DXT dxt
Enter the trace spacing (in ft or meters) on velocity
dataset after typing -DXT. Default is the velocity
dataset line header (Dx1000/1000).
-DZT dzt
The depth sample spacing (in ft or meters) on velocity
dataset. Default is to use velocity dataset line
header (Dz1000/1000).
-V Enter -V for a verbose printout.
-h Enter -h for online help. Program will terminate after
printing this.
-kmpw.crd"\
This keyword, -kmpw.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 following the
embedded menu cards must be present as shown.
Description of Parameters
ENDTIMEMS endtime
Enter the end time in ms; it should be <= the maximum
time on input. Default is maximum time on input.
PADTIME padtime
Enter the amount of time in ms to zero pad traces.
Because the migration is not performed in the frequency
domain, this pad is not really necessary. Recommended
default is 0.
BEGTIMEMS begtime
Enter the beginnning time in ms. This should be a
positive value and is used mainly for model data.
Enter the input sample spacing in ms. Default is the line header
value.
TMUTE mute
Enter mute time in ms. The input data will be zeroed
preceding this time.
MINFREQHZ F2FREQHZ F3FREQHZ MAXFREQHZ f1 f2 f3 f4
Enter the points of a trapezoidal filter (in Hz).
MAX DEPTH zmax
Enter the maximum depth (ft or meters). No default.
Enter the output depth spacing (ft or meters). No default.
1ST DEPTH dep1
Enter the minimum depth (ft or meters) to migrate. This
can be used to reduce cost if only a depth swath is
desired.
2ND DEPTH dep2
Enter the maximum depth (ft or meters) to migrate. This
can be used to reduce cost if only a depth swath is
desired.
Enter the trace spacing (ft or meters) of the input seismic data.
No default.
BEG REC irbeg
Enter the first input record to use. Default is 1.
END REC irend
Enter the last input record to use. Default is number
of records in the line header.
REC INC irinc
Enter the record increment to use. Default is 1.
BEGTRACE itrbeg
Enter the first input trace in each record to use.
Default is 1.
ENDTRACE itrend
Enter the last input trace in each record to use.
Default is number of traces in the line header.
REF VELOC vref
Enter the reference velocity as specified to program
slnt. This must be correct.
EMERG ANG emerg
The traveltimes for the migration are generated from
ray tracing. The emergent angle (in degrees from vert-
ical) determines the initial span of the receiver rays
at the surface. These rays are generated between
-emerg angle to + emerg angle. Typical values are 30-60
degrees. This parameter should be chosen to be less
than the dipmax parameter. This does not affect the
rays traced from the plane wave source. No defaults.
Enter the
maximum angle to be used in ray tracing. It can be
larger than 90 degrees if the velocity gradients are
sufficient. No default.
MIG 1/2 AP nap
Enter the number of traces to include in migration half
aperture. No default.
Enter the depth spacing to be used in migration. The output is
resampled
from dzmig to dz. Run time depends on dzmig (not dz).
Watch spatial aliasing. No default.
YINC nrayinc
The scattered rays are traced at each each surface
location which is a multiple of nrayinc. For rapid
lateral velocity variations this number should be small
(3-9). For slowly varying velocities this number can
be larger (25-50).
ISMOOTH ismooth
Enter the velocity smoothing for ray tracer.
Recommended value is 3. If the input velocity field
needs extra smoothing, this value can be increased. If
the velocity field has been smoothed externally, you
may set this to 0.
ISTRIDE istride
The input trace stride. Every ISTRIDE trace will be
used in the migration. Default is 1. Values of 2-4
can be used in the iteration phase to help decrease
cost. Watch spatial aliasing!
#ANGLES numang
The number of angles (as in slnt). Must match input!
RT start
The starting angle in degrees (as in slnt). Must match
input!
INCREMENT inc
The angle increment in degrees (as in slnt). Must
match input!
SEE ALSO
mbs, startjob, beginjob, endjob, pwmvzn, fxpwmig, splitss,
slnt, angs
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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