NAME
slnt - Slant Stack
SYNOPSIS
slnt -Nindsn -Ooutdsn -Ggrpint \
-slnt.crd"\
REF.-VEL. NSTRT NEND DXREC FMAX NPAD TAPER-OUT TAPER-IN
vref nstrt nend dx fmax pad outside inside
VMUTE('/S) T0(MS) FARMP(MS) ZERMP(MS) PHASE EXPON
vmute t0 far_ramp zero_ramp phase expon
# ANGLES ANGL-STRT ANGL-INC
angs angstrt inc
0
"
#...|....1....|....2....|....3....|....4....|....5....|....6....|....7....|....8
STARTJOB
Create a file that looks like the above synopsis with the
following command:
catpat slnt > slnt.job
This job file will have some suggested parameter values
entered. Edit your slnt.job with vi to suit your needs and
submit slnt.job with the following command:
startjob slnt.job
DESCRIPTION
slnt is a program that uses a summing procedure to slant
stack seismic data records that are functions of time and
offset to produce records that are functions of time and
angle. The summing is done in the frequency-space (f-x)
domain. The input to slnt may be common shot, or common
receiver sorted records. The common source or receiver data
should be split spread data. If it is not, you may syn-
thesize this data by applying the the mbs program splitss to
cdp data and sorting back to the source or receiver domain.
Each output record will contain a set of traces where each
trace represents a particular angle. The output from slnt
is a set of tau-p seismograms. To produce common angle
seismograms, the tau-p data should be sorted (interchanging
traces and records) with mbs program memangs or program
angs. Additional inputs to slnt are command line arguments
and a set of parameters read from the embedded menu cards as
shown above.
Command line arguments
-Nindsn
Enter the dataset name after typing -N. The input may
be common shot, or common receiver sorted USP formatted
seismic data.
-Ooutdsn
Enter the output dataset name after typing -O. The
output will be USP-formatted seismic records, where
each record is a function of time and angle.
-Ggrpint
Enter the input group interval after typing -G. The
default is to use the group interval value from the
input line header. This value will not be placed in the
output line header.
-V Enter -V for a verbose printout.
-h Enter -h for online help. The program will terminate
after printing this.
-slnt.crd"\
This keyword, -slnt.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. The double quote following the embedded menu
cards must be present as shown.
Description of Parameters
REF.-VEL.vref
This is a reference velocity used in slant stacking.
The ray parameter which is used for each angle is com-
puted with this velocity by p = sin(theta)/vref , where
each theta is computed from the angle parameters below.
Typically, this velocity is chosen to be approximately
equal to the near surface velocity. The angles which
are computed are approximately equal to the physical
angles of a plane wave at the earth's surface.
NSTRTnstrt
The first record to use from the input data. Default
is 1.
NENDnend
The last record to use from the input data. The
default is the number of records on the input dataset.
DXRECdx
The spatial record increment in feet or meters. This
value represents: group spacing if common receiver
data; source spacing if common source data. There is
no default.
FMAXfmax
The maximum frequency (in Hz) expected for your data
and sampling rate. The maximum frequency is a hard
cutoff and should be >= that desired in migration pro-
cessing. There is no default.
NPADpad
The number of zero sample values to pad to avoid wrap
around in the slant stack. For plane waves going into
the stack, values for times before zero are taken from
a wrap-around at the bottom of the trace. Internally,
the program has already padded the data up to the next
power of 2. This pad is designed to ensure that suffi-
cient zeroed out values are provided. The recommended
value is 200.
TAPER-OUToutside
The outside taper width in traces. Tapering the edges
of the data will minimize edge effects. If this value
is blank or zero, no tapering will be done.
TAPER-INinside
The inside taper width in traces across the gap.
Default and recommended value is 0.
VMUTEvmute
This value is the muting velocity in ft/sec or m/sec.
This parameter will be used with the T0, FARMP, and
ZERMP parameters described below, to mute the first
breaks. If this value is blank or zero, no muting will
be done.
T0t0 This value is the zero offset starting time in ms for
muting the first breaks.
FARMPfar_ramp
This is the far offset time ramp in ms leading up to
velocity mute line. There is no default. If far_ramp
and zero_ramp are both zero, no muting will be done.
ZERMPzero_ramp
This is the zero offset time ramp in ms leading up to
velocity mute line. There is no default. If far_ramp
and zero_ramp are both zero, no muting will be done.
PHASEphase
This value is in degrees and is used to rotate the
phase. The default and the recommended value is 45
degrees.
EXPONexpon
The exponent for scaling. The data will be scaled by
t**expon to remove cylindrical spreading. The recom-
mended value is 1.0.
# ANGLESangs
This value specifies the number of angles desired on
output. These should be chosen such that they are sym-
metric about zero. For example, (number of angles = 81,
starting angle = -40 degrees, increment = 1 degrees)
would give coverage from -40 degrees through +40
degrees with the center angle being 0 degrees.
ANGLE-STRTangstrt
The starting angle in degrees. This value can be nega-
tive.
ANGLE-INCinc
The angle increment in degrees. This can be a frac-
tional amount.
COMMENTS
The following line header words are altered by slnt:
NumSmp NumTrc NumRec
SmpInt Format Dx1000
The following trace header words are altered by slnt:
RecNum TrcNum
The following line header and trace header words will be used
to contain information particular to a slnt dataset:
Line Header Contents
Word
CDPFld The number of angles
MutVel The mute velocity, if entered
WatVel The reference velocity
RATTrc The starting angle
RATFld The angle increment
Trace Header Contents
Word
DstUsg The reference velocity
DstSgn The angle
SrcPnt This will be set equal to SoPtNm from the input
StaCor The spatial record increment entered * record no. * angle
SEE ALSO
mbs, startjob, beginjob, endjob, splitss, angs, memangs,
pwmvzn, kmpw, fxpwmig
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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