NAME
dcray - performs seismic ray trace modeling in horizontally
layered isotropic, earth
SYNOPSIS
dcray [ -Nntap ] [ -Ootap ] [ -Wwtap ] [ -nsnsamp ] [
-ntntrc ] [ -sinsi ] [ -xminxmin ] [ -xmaxxmax ] [ -f1f1 ] [
-f2f2 ] [ -f3f3 ] [ -f4f4 ] [ -nintnint ] [ -npsnps ] [ -V ]
[ -? ] [ -h ]
DESCRIPTION
dcray computes a synthetic seismogram based on downward con-
tinuation principles in a horizontally layered isotropic
earth.
The complete Knott-Zoeppritz reflection coefficients are
used throughout the program and, due to the nature of the
computational algorithm, cross-over events are automatically
incorporated. Post-critical phase rotations are also
included as are 4th order NMO effects. Because the program
is very efficient, Backus averaging to decrease the number
of layers is not required. Thousands of layers may be input
to the program.
dcray gets both its data and its parameters from command
line arguments. These arguments specify the input, output,
the number of traces and samples, the sample interval, the
minimum and the maximum offsets, the source wavelet in fre-
quency domain (an Ormsby wavelet described with four corner
frequencies: f1,f2,f3, and f4), the number of interfaces
(NumberOfLayers - 1), and the number of horizontal slowness
values (the number of p's to do ray tracing. This is an
independent value from number of traces, but number of
traces must be greater than or equal to the number of p's.)
to do ray tracing. The suggested largest frequency, f4,
for the wavelet should be no larger than about 1/3 of the
Nyquist frequency.
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'.
This file is an ASCII file and contains four columns;
Depth, Vp (P-wave velocity), Vs (S-wave velocity), and
Rho (density).
An example format may be as the following:
200 6000 3000 2.24
220 6500 3100 2.22
The depth is the distance from the surface to the
interface. The units may be in meters or feet but
should be consistent with the exception of density.
The density must be in gr/cm^3.
-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). This
is a sis formatted data file that contains the output
synthetic seismogram.
-W wtap
Enter the name of the file that contains source
waveform, if it exists, immediately after typing -O.
This input file has two columns; first column the
values of the wavelet, second ASCII flags. These flags
can only be n or p. As in the following example:
5.76936E-05 n
2.59151E-04 n
6.59444E-04 n
1.36931E-03 n
2.55024E-03 n
4.32851E-03 n
6.68172E-03 n
9.40006E-03 n
1.21878E-02 n
1.48614E-02 n
1.50000E-02 p
1.48614E-02 n
1.21878E-02 n
9.40006E-03 n
6.68172E-03 n
4.32851E-03 n
2.55024E-03 n
1.36931E-03 n
6.59444E-04 n
2.59151E-04 n
5.76936E-05 n
p shows the symmetry axis where you would like to
center your reflection coefficient and n stands for
nuetral values.
-ns nsamp
Number of samples in the output seismogram. Default =
none
-nt ntrc
Number of output traces. Default = none
-si si
Sample interval in mils. Minimum is 1 millisecond.
Default = 1
-xmin xmin
Distance between source and the first receiver in shot
gathers or the smallest shot-receiver distance in a
cdp. Units should be consistent with the velocity
units. Default = 0
-xmax xmax
Distance between source and the last receiver in shot
gathers or the largest shot-receiver distance in a cdp.
Units should be consistent with the velocity units.
Default = 20000
-f1 f1
The first corner frequency value of the Ormsby wavelet
in Hertz. Default = 5.
-f2 f2
The second corner frequency value of the Ormsby wavelet
in Hertz. Default = 10.
-f3 f3
The third corner frequency value of the Ormsby wavelet
in Hertz. Default = 40.
-f4 f4
The fourth corner frequency value of the Ormsby wavelet
in Hertz. Default = 60.
-nint nint
The number of interfaces (NumberOfLayers-1). Default =
1.
-nps nps
The number of horizontal slowness (p) values to perform
ray tracing. This value should not exceed the value
given for the number of traces. In most cases 10, is a
good choice. Default = 10.
-V Enter the command line argument '-V' to get additional
printout.
-?/-h
Enter the command line argument '-?' or -h to get
online help. The program terminates after the help
screen is printed.
BUGS
unknown
AUTHOR
Matt Hakan Karazincir, Amoco-EPTG
COPYRIGHT
copyright 2001, Amoco Production Company
All Rights Reserved
an affiliate of BP America Inc.
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