NAME
angsyn - uses least squares to predict amplitudes of CDP
data from a reflectivity equation.
SYNOPSIS
angsyn [ -Nntap ] [ -Ootap ] [ -vRMS Velocity File ] [ -rs ]
[ -re ] [ -as ] [ -ae ] [ -md ] [ -xt ] [ -? ] [ -h ]
DESCRIPTION
angsyn predicts the amplitudes of seismic data through an
unconstrained least squares fit of the input data to a
reflectivity equation. Input may be either angle-dependent
gathers (angle-T domain) created by program ANGST or stan-
dard (X-T domain) CDPs. The amplitudes are predicted by
fitting the input amplitudes, sample by sample, in an iso-
time sense, to a linearized form of the Knott-Zoeppritz
equation. The output contains only the predicted amplitudes
in a data set the same size as the input.
It is important to note that the output data is primarily
valuable for QC only. A stack of the output data will be
same as a stack of the input data, since both the prediction
and stacking procedure "assume" that the noise on the CDP is
uncorrelated and averages to zero. If, however, the input
data is angle gathers, the incremental stacks of the gathers
to produce angle-limited stacks WILL be somewhat different.
Attributes created from the output data will be the same as
those computed from the input as long as the reqression used
to compute the attributes is based on the same
equation(given below). Note: when running inside XIKP the 0
connector is for the input data, the 1 connector is for the
output data, and the 3 connector is for the RMS P-velocity.
The basis equation for the least squares regression is given
by
R(t) = A + D*tan^2(theta) + E*tan^2(theta)*sin^2(theta), where
theta is the incident angle at time t and "^2" denotes
squaring. The coefficients A, D, and E are computed by
minimizing the difference between the observed amplitude
values and the values predicted by R(t). Once the coeffi-
cients are computed, the R(t) may then be computed for the
given angle field.
Program angsyn gets its data and parameters from command
line arguments. These arguments specify the input data and
velocity files, the output data set, and other computation
limitations.
Command line arguments
-N ntap
Enter the input data set name immediately after typing
-N. This input file should include the complete path
name if the file resides in a different directory.
Example -n/b/tsp/dummy tells the program to look for
file 'dummy' in directory '/b/tsp'. (Default = stdin).
Note: when running inside XIKP the 0 connector is for
the input data, the 1 connector is for the output data,
and the 3 connector is for the RMS P-velocity.
-O otap
Enter the output data set name immediately after typing
-O. Specify the full path to write the file to a
directory other than the current working directory.
(Default = stdout ). Note: when running inside XIKP the
0 connector is for the input data, the 1 connector is
for the output data, and the 3 connector is for the RMS
P-velocity.
-v RMS velocity file
Enter the name of the file containing the RMS veloci-
ties corresponding to the input data set, one velocity
record for each CDP. This is typically the output from
program VELIN or program VOMIT. (Default = NONE. This
parameter is REQUIRED when the input is X-T domain. It
will otherwise be ignored). Note: when running inside
XIKP the 0 connector is for the input data, the 1 con-
nector is for the output data, and the 3 connector is
for the RMS P-velocity.
-rs start record
Enter the sequential number of the record on which to
begin processing. All data prior to this record will
be skipped and not output. (Default = first)
-re end record
Enter the sequential number of the record on which to
end processing. All data following this record will be
skipped and not output. (Default = last)
-as mininum angle
Enter the minimum incident angle, in degrees, to limit
the data values used in the weighted stacks. Data
corresponding to incident angles less than this value
are ignored. (Default = 0 degrees)
-ae maximum angle
Enter the maximum incident angle, in degrees, to limit
the data values used in the weighted stacks. Data
corresponding to incident angles greater than this
value are ignored. (Default = 45 degrees)
-md ray tracing mode for X-T input
Enter the flag to indicate the type of ray-tracing
solution desired. A value of 0 gives a straight ray
solution. A value of 1 gives a curved ray solution.
A value of 2 give a perturbed curved ray solution ein
the smooth curved ray solution is "perturbed" in accor-
dance with the true input velocity function. (Default
= 1).
-xt X-T Domain flag
If this flag is present, the input data are assumed to
be in the X-T domain and ray tracing will be used to
define the incident angle field for the regression pro-
cedure. (Default = no, the input data are assumed to be
in angle-T domain.)
-? Enter the command line argument '-?' to get online help.
The program terminates after the help screen is printed.
-h Same as -?, except a list of the output traces is also
printed. The program terminates after the help screen is
printed.
SEE ALSO
angst(1)
square(1)
attin(1)
sscale
sscaleu
REFERENCES
Aki, K. and Richards, P.G., 1980, Quantitave Seismology:
Theory and Methods, Freeman, San Francisco.
Castagna, J.P., Batzle, M.L., and Eastwood, R.L., 1985,
Relationships Between Compressional-Wave and Shear-Wave
Velocities In Clastic Silicate Rocks, Geophysics, Vol. 50,
pp 571-581.
Castagna, J.P., Batzle, M.L., and Kan, T.K., 1992, Rock Phy-
sics - The Link Between Rock Properties and AVO Response in
Offset-Dependent Reflectivity - Theory and Practice of AVO
Analysis, J.P. Castagna and M.M. Backus (eds), Society of
Exploration Geophysics.
Castagna, J.P., and Smith,, S.W., 1994, Comparison of AVO
Indicators: A Modeling Study, Geophysics, Vol. 59, pp
1849-1855.
Smith, G.C. and Gidlow, P.M., 1987, Weighted Stacking for
Rock Property Estimation and Detection of Gas, Geophysical
Prospecting, Vol. 35, pp 993-1014.
Thomsen, L.P., 1982, Amplitude Vs. Range Attributes: Interim
Report, Amoco Production Company Research Department Report
T82-E-10.
Thomsen, L.A. and Hanson, K.E., 1985, Linear RDA: S and P,
Amoco Production Company Research Department Report T86-E-
44.
AUTHOR
Richard Crider STAT Houston
COPYRIGHT
copyright 2001, Amoco Production Company
All Rights Reserved
an affiliate of BP America Inc.
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