NAME
avoan - amplitude versus offset analysis and balance
SYNOPSIS
avoan [ -N ntap ] [ -O otap ] [ -s start time ] [ -e end
time ] [ -rs start record ] [ -re end record ] [ -ns start
trace ] [ -ne end trace ] [ -xmin min offset ] [ -xinc
offset increment ] [ -noff num offsets ] [ -slope slope ] [
-icept intercept ] [ -sfile xgraph filname ] [ -anl ] [
-func function type ] [ -amp amplitude type ] [ -decay
amplitude decay ] [ -comp fraction ] [ -V ] [ -? ]
DESCRIPTION
avoan performs an amplitude analysis and/or application on
the input dataset. If the -anl flag is used, avoan only per-
forms analysis. If either of the -slope or -icept values
are specified, only scalar application is performed. By
default, both analysis and application are performed with
two consecutive passes over the input data. Two pass opera-
tion is only allowed on disk (not piped) input.
An analysis of the data is performed as follows: Using the
user-supplied xmin, xinc, and noff, the program cumputes the
amplitude for each offset. The amplitude versus offset
curve is generated once for the whole dataset, i.e. job con-
stant operation is always performed. The analysis results
are written to an auxiliary file. The auxiliary file can be
plotted on a workstation with the xgraph command.
avoan also performs an offset variable amplitude scaling.
The scaling is keyed on the absolute value of the DstSgn
trace header and uses the following algorithm:
1. A linear function is fit to the measured amplitude.
The measured amplitude is determined by the -amp option
and may be either average absolute, rms, or geometric
mean amplitudes. The linear fit is optimum in a
least-squared error sense. This analysis is limited by
the -rs, -re, -ns, -ne, -s, and -e arguments;
2. The desired amplitude curve is constructed by com-
bining an intercept of the linear fit and a slope
derived from the amplitude decay at the last offset
supplied by a user (-decay option);
3. For each offset, a scalar is derived as a weighted
sum (with the weighting coefficient taken from the
-comp option) of two scaling coefficients computed by
a) dividing the desired amplitude by the amplitude of
the least-square fit and b) dividing the desired ampli-
tude by the average amplitude at this offset;
4. The entire dataset is scaled with the calculated
function;
The resulting output amplitude curve has the same intercept
as the input-amplitude fitting curve, a slope that provides
the specified amplitude decay at the last offset, and its
maximum deviation from the desired amplitude curve is con-
trolled by the weighting coefficient.
Note that an exponential amplitude scaling is also available
as the -func exp option. With this option, the output
amplitude curve will also have an additional property. The
amplitude decay between any two neighboring offsets will be
the same percentage change.
Application only mode is turned on when the user specifies
either the -slope or the -icept arguments. Application mode
performs one pass application. Piped input is allowed. The
-anl, -decay, -comp, -amp, -rs, -re, -ns, -ne, -s, and -e
arguments are disabled. The scalar applied is
1/(slope*x+icept) for -func lin. The scalar applied is
1/exp(slope*x+icept) for -func exp.
Note that simply specifying the values from an analysis run
will scale the data to 1.0. In order to leave the overall
data amplitude unchanged, the slope/intercept values from an
analysis run must be changed. For the exponential option,
specify -icept as 0. and -slope equal to the analysis value.
For the linear option, specify -icept as 1.0 and the -slope
as analysis_slope/analysis_intercept.
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'.
Note that combined scalar analysis and application is
not allowed with a piped input (the program has to make
two data passes, one for analysis and one for scaling).
-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).
-s start time
Enter the start time of the analysis window. The
default is the beginning of the trace. Scaling, if
requested, will be applied to the whole trace.
-e end time
Enter the end time of the analysis window. The default
is the end of the trace.
-rs start record
Enter the analysis starting sequential record. Default
is to start amplitude analysis on the first record.
All records are scaled.
-re end record
Enter the analysis ending sequential record. Default
is to stop amplitude analysis on the last record. All
records are scaled.
-ns start trace
Enter the analysis start trace number. The default is
the first trace of the record. All traces are scaled.
-ne end trace
Enter the analysis end trace number. The default is the
last trace of the record. All traces are scaled.
-xmin min offset
Enter the minimum absolute offset in the dataset
(DstSgn header). Required.
-xinc offset increment
Enter the offset increment. Usually the same as the
group interval. Required.
-noff num offset
Enter the number of offsets in the dataset. Required.
-slope amplitude slope
If specified, this value of the data slope will be
assumed rather than be derived from the data. No data
analysis will be performed. AVOAN will only scale the
data. This option is incompatible with the -anl
option.
-icept amplitude intercept
If specified, this value of the scalar intercept will
be assumed rather than be derived from the data. No
data analysis will be performed. AVOAN will only scale
the data. This option is incompatible with the -anl
option.
-sfile xgraph filname
Enter the name of the xgraph file. Default
'xgraph.xgr'
-anl The '-anl' option turns off the scaling operation. No
traces are output.
-func function type
This option indicates what function type, linear or
exponential, will be used for the desired amplitude vs
offset dependence. Only two values of the parameter
function type are allowed lin (default) and exp.
-amp amplitude type
The '-amp' option defines the type of amplitude used
for the linear fit - average absolute, rms, or
geometric mean amplitudes. Thus, the only legal values
for amplitude type are abs, rms, or geom. The default
amplitude type is abs.
-decay amplitude decay
The '-decay' option specifies the desired amplitude
decay (%). The value specified is the far offset
amplitude reduction compared to the zero offset ampli-
tude. For example, a value of -15 will cause the far
offset amplitude to be 15% lower than the zero offset
amplitude. The value of the amplitude decay can not
be less or equal to -100 (which would cause the output
amplitude to be 0.). The default value is -5.
-comp fraction
The '-comp' option specifies a compression fraction.
Mean data values may be forced to the desired output
amplitude for each offset. Alternately, only the
overall trend of amplitudes may be changed. The
weighting coefficient is used to calculate the
amplitude-scaling factor (see a description of the
algorithm). It ranges between 0. and 1. For the
fraction equal 1., the mean output level will be fully
scaled to the desired level. For the fraction less
than 1., the output data will partially scaled.
-V Enter the command line argument '-V' to get additional
printout.
-? Enter the command line argument '-?' to get online
help. The program terminates after the help screen is
printed.
EXAMPLES
A simple analysis amd scaling on a disk file input:
avoan -Ncdps.usp -Oavoan.usp -xmin186 -xinc25 -noff184
An example of an amplitude analysis follows. The analysis
results can be displayed with "xgraph shots.xgr"
avoan -Nshots.usp -anl -sfile shots.xgr -xmin186 -xinc25
-noff184 -V
BUGS
No known bugs at present.
SEE ALSO
gasp
AUTHOR
Steve Markley (x3613) at Richard Crider's request.
Dmitriy Repin (x4893) - code modification:
The following options were added to the program: '-
amp', '-decay', '-comp'. The option '-linamp' was
changed to '-func' and the linear scaling became
default.
COPYRIGHT
copyright 2001, Amoco Production Company
All Rights Reserved
an affiliate of BP America Inc.
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