DOCUMENTATION
SYNOPSIS
PERL PROGRAM NAME: SUVELAN - compute stacking velocity semblance for cdp gathers
AUTHOR: Juan Lorenzo (Perl module only)
DATE: Dec 1 2013, Nov. 2, 2018, Chang Liu
DESCRIPTION:
Version: USE
NOTES
Distances (and velocities) need to be scaled by the user
a scaling factor is needed to match
scalel found in data headers
suvelan DOES not take scaleco or scalel into consdieration
automaticallyExamples
SEISMIC UNIX NOTES
SUVELAN - compute stacking velocity semblance for cdp gathers
suvelan <stdin >stdout [optional parameters]
Optional Parameters:
nv=50 number of velocities
dv=50.0 velocity sampling interval
fv=1500.0 first velocity
anis1=0.0 quartic term, numerator of an extended quartic term
anis2=0.0 in denominator of an extended quartic term
smute=1.5 samples with NMO stretch exceeding smute are zeroed
dtratio=5 ratio of output to input time sampling intervals
nsmooth=dtratio*2+1 length of semblance num and den smoothing window
verbose=0 =1 for diagnostic print on stderr
pwr=1.0 semblance value to the power
Notes:
Velocity analysis is usually a two-dimensional screen for optimal values of
the vertical two-way traveltime and stacking velocity. But if the travel-
time curve is no longer close to a hyperbola, the quartic term of the
traveltime series should be considered. In its easiest form (with anis2=0)
the optimizion of all parameters requires a three-dimensional screen. This
is done by a repetition of the conventional two-dimensional screen with a
though the function is no more a polynomial. When screening for optimal
values the theoretical dependencies between these paramters can be taken
into account. The traveltime function is defined by
1 anis1
t^2 = t_0^2 + --- x^2 + ------------- x^4
v^2 1 + anis2 x^2
The coefficients anis1, anis2 are assumed to be small, that means the non-
hyperbolicity is assumed to be small. Triplications cannot be handled.
Semblance is defined by the following quotient:
n-1
[ sum q(t,j) ]^2
j=0
s(t) = ------------------
n-1
n sum [q(t,j)]^2
j=0
where n is the number of non-zero samples after muting.
Smoothing (nsmooth) is applied separately to the numerator and denominator
before computing this semblance quotient.
Then, the semblance is set to the power of the parameter pwr. With pwr > 1
the difference between semblance values is stretched in the upper half of
the range of semblance values [0,1], but compressed in the lower half of
it; thus, the few large semblance values are enhanced. With pwr < 1 the
many small values are enhanced, thus more discernible against background
noise. Of course, always at the expense of the respective other feature.
Input traces should be sorted by cdp - suvelan outputs a group of
semblance traces every time cdp changes. Therefore, the output will
be useful only if cdp gathers are input.
Credits:
CWP, Colorado School of Mines:
Dave Hale (everything except ...)
Bjoern Rommel (... the quartic term)
SINTEF, IKU Petroleumsforskning
Bjoern Rommel (... the power-of-semblance function)
Trace header fields accessed: ns, dt, delrt, offset, cdp
Trace header fields modified: ns, dt, offset, cdpCHANGES and their DATES
sub Step
collects switches and assembles bash instructions by adding the program name
sub note
collects switches and assembles bash instructions by adding the program name
sub clear
sub anis1
sub anis2
sub dtratio
sub dv
defines the size of the velocity steps
to use in the semblance analysissub first_velocity
defines the first velocity value to use in the semblance analysis
sub fv
defines the first velocity value to use in the semblance analysis
sub nsmooth
sub number_of_velocities
sets the number of velocitiessub nv
sets the number of velocitiessub pwr
sub smute
sub velocity_incrementdv
defines the size of the velocity steps
to use in the semblance analysissub verbose
sub get_max_index
max index = number of input variables -1