ishot - an array specifying the directions rays are to be traced
from the shot points listed in the arrays xshot and zshot; the
following code is used:
(1) 0 - no rays are traced
(2) -1 - rays are traced to the left only
(3) 1 - rays are traced to the right only
(4) 2 - rays are traced to the left and right
(default: 0)
iraysl - use the array irayt to select which ray groups listed
in the array ray are to be traced for a particular shot point
(default: 0)
irayt - an array selecting those ray groups listed in the array
ray which are active for a particular shot point listed in the
arrays xshot and zshot. If there are n ray groups listed in
the array ray, then the jth ray group for the ith shot is
referred to in the (2n(i-1)+j)th element of irayt for rays
traced to the left , and in the (2n(i-1)+n+j)th element of
irayt for rays traced to the right. You must specify values of
irayt for each group and for each direction regardless of the
values of ishot (default: 1)
ifast - use a Runge-Kutta routine without error control to solve
the ray tracing equations and a look-up/interpolation routine
to evaluate certain trigonometric functions; with ifast=0, a
Runge-Kutta method with error control and the intrinsic
trigonometric functions are used. Using ifast=1 is about 30-40%
faster and provides essentially the same accuracy as ifast=0
(default: 1)
Note: ifast=1 is intended to be used for all routine modelling
and ifast=0 only to test a final model or if ifast=1
obviously fails
i2pt - perform two-point ray tracing, i.e., determine the ray take-
off angles that connect sources and observed receiver locations
within each ray group; the receiver locations are obtained from
the file tx.in for those picks that have the same integer code
as specified in the array ivray for the ray group; if i2pt=2,
only rays which reflect off the appropriate floating reflector
specified in the array frbnd (if frbnd>0) are traced (default: 0)
iturn - an array corresponding to the ray groups listed in the
array ray to trace rays only to their turning or reflection
point in the search mode; if a refracted or head wave ray group
is to contain a reflection(s) before it turns (specified using
nrbnd and rbnd), then iturn=0 must be used (default: 1)
isrch - search again for the take-off angles of a ray group if
the same ray code is listed more than once for the same shot in
the array ray; isrch=1 must be used if the take-off angles of
two or more ray groups with the same ray code are different
because of multiple reflections and/or conversions specified by
nrbnd, rbnd, ncbnd,and cbnd (default: 0)
istop - stop tracing any ray which reflects off a boundary not
specified in the arrays ray or rbnd; if istop=2, rays are also
stopped if they enter a layer deeper than that specified by the
ray code in the array ray, i.e., the layer number is greater
than L and the ray code is L.n, where n=0, 1, 2, or 3
(default: 1)
idiff - continue to trace headwaves along a boundary even if the
velocity contrast across the interface is no longer positive,
in which case headwaves emerge parallel to the boundary (idiff=1);
if idiff=2, initiate a headwave ray group even if there is no
critical point (or it is not found) to model diffractions along
the top of a low-velocity layer (default: 0)
ibsmth - apply a simulation of smooth layer boundaries (1) or
apply the simulation and plot the smoothed boundaries (2);
ibsmth=2 has no effect if isep>1 (default: 0)
insmth - an array listing the layer boundaries for which the smooth
layer boundary simulation is not to be applied, or only applied
outside the model distances xminns and xmaxns, when ibsmth=1
or 2, (default: 0)
imodf - use the velocity model in the file v.in instead of the
model in part (5) of the file r.in (default: 0)
xshot - an array containing the x-coordinates (km) of the shot
points (default: 0.0)
zshot - an array containing the z-coordinates (km) of the shot
points (default: a very small distance below the model surface)
ray - an array containing the ray groups to be traced; the
following code is used:
(1) L.1 - rays which refract (turn) in the Lth layer
(2) L.2 - rays which reflect off the bottom of the Lth layer
(3) L.3 - rays which travel as head waves along the bottom
of the Lth layer
(4) L.0 - ray take-off angles supplied by the user in the
arrays amin and amax
nray - an array containing the number of rays to be traced for
each ray group in the array ray (default: 10; however, the
default is the first element of nray for all ray groups if only
one value is specified)
space - an array which determines the spacing of take-off angles
between the minimum and maximum values for each ray group in
the array ray. For space=1, the take-off angles will be
equally spaced; for space>1, the take-off angles will be
concentrated near the minimum value; for 0<space<1, the
take-off angles will be concentrated near the maximum value
(default: 1; however, space=2 for a reflected ray group if
specified as L.2 in the array ray)
amin, amax - arrays containing minimum and maximum take-off
angles (degrees); measured from the horizontal, positive
downward and negative upward (for rays traveling left to right
or right to left); used for ray groups specified by ray=1.0
nsmax - an array containing the maximum number of rays traced
when searching for the take-off angles of the ray groups in the
array ray (default: 10; however, the default is the first
element of nsmax for all ray groups if only one value is
specified)
n2pt - maximum number of iterations during two-point ray tracing
(i2pt>0); this is the maximum number of rays traced for each
receiver to determine the take-off angle of the ray that
connects the source and receiver (default: 5)
x2pt - distance tolerance (km) for two-point ray tracing; less than
n2pt rays will be traced for a particular receiver if a ray end
point is within x2pt of the receiver location
(default: (xmax-xmin)/2000)
crit - head waves are generated if a down-going ray in the search
mode has an angle of incidence at the bottom of the Lth layer
within crit degrees of the critical angle when ray=L.3
(default: 1)
hws - the spacing (km) of rays emerging upward from the bottom of
the Lth layer when ray=L.3 (default: (xmax-xmin)/25)
nhray - maximum number of rays traced for a head wave ray group
(default: pnrayf)
aamin - minimum take-off angle (degrees) for the refracted ray
group in the first layer (default: 5)
aamax - maximum take-off angle (degrees) for reflected ray groups
specified as L.2 in the array ray (default: 85)
stol - if a ray traced in the search mode is of the correct type
and its end point is within stol (km) of the previous ray
traced in the search mode, then the search for that ray type is
terminated; a value of stol=0 will ensure that nsmax rays are
always traced in the search mode (default: (xmax-xmin)/3500)
xsmax - for reflected ray groups specified as L.2 in the array
ray, determine the minimum take-off angle using the search mode
so that the maximum range for this ray group is xsmax (km) if
iturn=0 or the maximum offset of the reflection point is
xsmax/2 (km) if iturn=1; for head wave ray groups specified as
L.3 in the array ray, the maximum offset of the point of
emergence from the head wave boundary is xsmax (km); xsmax=0
will ensure that the take-off angle of the reflected ray which
grazes off the bottom of the Lth layer is determined and head
waves are traced along the Lth boundary until the edge of the
model is reached (default: 0.0)
nrbnd - an array containing the number of reflecting boundaries
for each ray group in the array ray (default: 0)
rbnd - an array containing the reflecting boundaries specified in
the array nrbnd; the following code is used:
(1) L - ray traveling downward is reflected upward off the
bottom of the Lth layer
(2) -L - ray traveling upward is reflected downward off the
top of the Lth layer
ncbnd - an array containing the number of converting (P to S or S
to P) boundaries for each ray group in the array ray (default:
0)
cbnd - an array containing the converting boundaries specified in
the array ncbnd; the following code is used:
(1) i - ray will convert from its present wave type (P or
S) at the ith layer boundary encountered
(2) 0 - ray will leave the source as an S-wave
frbnd - an array containing the floating reflecting boundaries
for each ray group in the array ray; the values of frbnd
correspond to the order in which the reflectors are listed in
the file f.in (default: 0)
pois - an array containing the value of Poisson's ratio for each
model layer; a value of 0.5 signifies a water layer with a
corresponding S-wave velocity of zero (default: 0.25;
however, the default is the first element of pois for all
layers if only one value is specified)
poisl, poisb - arrays specifying the layers and block numbers,
respectively, of model trapezoids within which Poisson's ratio
is modified over that given by pois using the array poisbl; for
poisb, the trapezoids with a layer are numbered from left to
right
poisbl - an array containing the value of Poisson's ratio for the
model trapezoids specified in the arrays poisl and poisb
overriding the values assigned using the array pois
npbnd - number of points at which each layer boundary is
uniformly sampled for smoothing if ibsmth=1 or 2 (default:
100)
nbsmth - number of applications of a three-point averaging filter
to each layer boundary if ibsmth=1 or 2 (default: 10)
xminns, xmaxns - minimum and maximum model distance over which the
layer boundaries listed in the array insmth are not to be smoothed
using ibsmth=1 or 2 (defaults: smooth boundaries between xmin and
xmax)
step - controls the ray step length in the solution of the ray
tracing equations according to the relationship
step length (km) = step*v/(|vx|+|vz|)
where v is velocity and vx and vz are its partial
derivatives with respect to x and z (default: 0.05)
smin, smax - minimum and maximum allowable ray step length (km)
(defaults: (xmax-xmin)/4500, (xmax-xmin)/15)