NAME
vfilt3d - module to do generalized (velocity, azimuth, fre-
quency) filtering of 3D post stack data.
SYNOPSIS
vfilt3d [ -Nntap ] [ -Ootap ] [ -dtdt ] [ -dxdx ] [ -dydy ]
[ -dzdz ] [ -v1v1 ] [ -v2v2 ] [ -v3v3 ] [ -v4v4 ] [ -a1a1 ]
[ -a2a2 ] [ -a3a3 ] [ -a4a4 ] [ -f1f1 ] [ -f2f2 ] [ -f3f3 ]
[ -f4f4 ] [ -pass ] [ -V ] [ -? ] [ -h ]
DESCRIPTION
performs a 2D FFT of the input dataset, passes or rejects
data within a specified range of frequency, velocity and
azimuth, and performs an inverse 2D FFT. Using velocity as
an example, though the following holds true for azimuth and
frequency as well, a cosine taper is applied from -v1 to
-v2 and again between -v3 and -v4 . Data in the range
-v2 through -v3 is rejected or passed as requested. The
input to this routine is the frequency slices formed by the
following process:
fftpack -Ndatain |
ttds3d -ND txy -OD xyt |
vfilt3d [parameters] |
ttds3d -ND xyt -OD txy |
fftpack -R |
hdrswap -N2 datain -O dataout
vfilt3d
vfilt3d gets both its data and its parameters from command
line arguments. These arguments specify the input, output,
the temporal or depth sample interval of the post stack 3D
dataset being used, the in-line and cross-line spacing, the
velocity, azimuthal and frequency filter points, the
pass/reject flag, 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).
-dt dt
Enter the temporal sample interval [ms] of the 3D post
stack dataset being filtered. There is NO default.
This parameter must be filled out or the routine will
abort.
-dz dz
Enter the depth sample interval [m] of the 3D post
stack dataset being filtered. If present, all parame-
ters input to this run are assumed to be measured in
terms of a depth section input. If not present the
input is assumed to be in time.
-dx dx
Enter the in - line spacing of the 3D post stack
dataset being filtered. This is the distance between
traces within a record on the dataset input to fftpack
. The default is 25.0 [units].
-dy dy
Enter the cross - line trace spacing of the 3D post
stack dataset being filtered. This is the distance
between records on the dataset input to fftpack . The
default is 25.0 [units].
-a1 a1
Enter lower azimuth taper start. A cosine taper will
be applied between this azimuth and that entered at -
a2 below. Note that the azimuth is measured with
respect to the (Kx,Ky) plane with zero degrees lying
along the Kx axis and 90 degrees along the KY axis.
Valid entries are from zero to 359 degrees. Default
[0.0]
-a2 a2
Enter lower azimuth taper end. A cosine taper will be
applied between this azimuth and that entered at -a1
above. Data between this azimuth an -a3 below will
be 100 percent passed / rejected as indicated by the
-pass entry below. Default [0.0]
-a3 a3
Enter upper azimuth taper start. A cosine taper will
be applied between this azimuth and that entered at -
a4 below. Data between this azimuth an -a2 above
will be 100 percent passed / rejected as indicated by
the -pass entry below. Default [0.0]
-a4 a4
Enter upper azimuth taper end. A cosine taper will be
applied between this azimuth and that entered at -a3
above. Default [0.0]
-f1 f1
Enter lower frequency taper start. A cosine taper will
be applied between this frequency and that entered at
-f2 below. Default [0.0]
-f2 f2
Enter lower frequency taper end. A cosine taper will
be applied between this frequency and that entered at
-f1 above. Data between this frequency an -f3 below
will be 100 percent passed / rejected as indicated by
the -pass entry below. Default [0.0]
-f3 f3
Enter upper frequency taper start. A cosine taper will
be applied between this frequency and that entered at
-f4 below. Data between this frequency an -f2 above
will be 100 percent passed / rejected as indicated by
the -pass entry below. Default [0.0]
-f4 f4
Enter upper frequency taper end. A cosine taper will
be applied between this frequency and that entered at
-f3 above. Default [0.0]
-v1 v1
Enter lower velocity taper start. A cosine taper will
be applied between this velocity and that entered at
-v2 below. Units are expected in feet or meters per
second for time and feet per foot or meters per meter
for depth. Default [0.0]
-v2 v2
Enter lower velocity taper end. A cosine taper will be
applied between this velocity and that entered at -v1
above. Data between this velocity an -v3 below will
be 100 percent passed / rejected as indicated by the
-pass entry below. Units are expected in feet or
meters per second for time and feet per foot or meters
per meter for depth. Default [0.0]
-v3 v3
Enter upper velocity taper start. A cosine taper will
be applied between this velocity and that entered at
-v4 below. Data between this velocity an -v2 above
will be 100 percent passed / rejected as indicated by
the -pass entry below. Units are expected in feet or
meters per second for time and feet per foot or meters
per meter for depth. Default [0.0]
-v4 v4
Enter upper velocity taper end. A cosine taper will be
applied between this velocity and that entered at -v3
above. Units are expected in feet or meters per second
for time and feet per foot or meters per meter for
depth. Default [0.0]
-pass
Enter the command line argument '-pass' to pass data
within the region described by the velocity, azimuth
and frequency parameters above. If not present the
default is to reject the data described.
-V Enter the command line argument '-V' to get additional
printout.
-? Enter the command line argument '-?' or -h or -help
to get online help. The program terminates after the
help screen is printed.
DISCUSSION
This routine uses a full complex fft and runs a little
slower than vfilt3d . The azimuthal rejection characteris-
tics of this routine are superior to vfilt3d . When
parameterizing for your dataset remember [ V = f / k ] is
the assumed relationship between velocity, frequency and
wavenumber. In this expression k is formed by using the Kx
and the Ky projections to calculate a radial wavenumber
(Kr). If you substitute into this expression your Nyquist
wavenumber along any axis you can calculate at what fre-
quency data aligned at the velocity of interest will alias
[where the velocity filter hits the edge of the transform].
An example time event velocity calculation would be:
delta time = 120 ms
delta distance = 1250 meters
velocity = 1250 /.120 = 10416 m/sec
Parameters such as -v1 8000 -v2 8200 -v3 12700 -v4 12900
would adequately filter out / or pass the above event
depending on your use of the -pass parameter.
An example depth event velocity calculation might look like:
delta depth = 1140 meters
delta distance [horizontal] = 100 meters
psuedo velocity = 0.08772 meters / meter
Parameters such as -v1 0.05 -v2 0.07 -v3 1.0 -v4 1.1 would
adequately filter out / or pass the above event depending on
your use of the -pass parameter.
Alternately you could use dip angles by converting to a
psuedo velocity using:
v1 = 1 / tan(85) v2 = 1 / tan(79) v3 = 1 /
tan(45) v4 = 1 / tan(40)
which would remove energy on a depth section between dips of
45 and 79 degrees. In this case make sure the steepest dips
are associated with the slowest velocities.
There are NO defaults for the filter taper parameters.
All desired filter information must be explicitly entered on
the command line. To do velocity filtering only simply
fill out only the velocity taper information. When doing
azimuthal filtering be certain to define your filter control
points in a counter-clockwise rotation. The is no provision
in the code for tapering in azimuth across the 0/360 boun-
dary. Be sure to make sure your taper zone does not include
this zone.
BUGS
Unknown.
SEE ALSO
fftpack(1) qdslice(1) ttds3d(1) fkrad(1) fkshape(1)
fkkstrip(1) vfilt3da(1)
AUTHOR
Dennis Yanchak [GUPCO] USP version by P.G.A. Garossino
[APR:3932]
COPYRIGHT
copyright 2001, Amoco Production Company
All Rights Reserved
an affiliate of BP America Inc.
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