bgar - BSU program for gain recovery, spherical divergence and exponential gain.
bgar [ -h | infile | rmin | rmax | dbu ]
Basic Seismic Utilities (BSU) computes an amplitude decay envelope over a user provided RANGE interval. The envelope is corrected for spherical divergence, converted to decibels, and a linear fit performed. The user may then apply the recommended gain correction, or over ride it with their own choice. The spherical divergence and exponential gain corrections are applied to the entire data set, (not just the interval of analysis). The data are not filtered before hand, so the decay measurements are a single result for the entire available bandwidth. If you want to measure inelastic decay as a function of frequency, then use program bamp. This program simply provides a broad-band view of amplitude decay as sensed by the summed absolute value amplitude of each trace on a survey. A PostScript plot of the linear regression is output (requires PLPLOT package be installed). C-Language Version.
The difference between bgaz.c and bgar.c is largely in the specification of the gate within which amplitude analysis is conducted (depth vs range specification). In both cases range beyond the reference controls the application of the gain recovery. The other difference is in the way the amplitude envelope is computed (peak-peak maximum in bgaz, sum of absolute values in each trace, bgar). If one prefers this latter estimate in a down-hole survey, then bgar could be run on down-hole data, the only inconvenience being a slight depth <--> range conversion is specifying the gate.
Options
|
-h |
Online help giving details on command line arguments |
infile1
Input file name
|
rmin |
The minimum range (relative to the source) for amplitude analysis. | ||
|
rmax |
The maximum range (relative to the source) for amplitude analysis. | ||
|
dbu |
Gain recovery to apply (dB/meter). If not provided on the command line, decay analysis will be displayed before prompting for a value. |
NOTES:
If invoked with no options, will prompt user for input
parameters. The amplitude model is given by:
A*r=Ao*ro*B*exp(alpha*(r-ro))
where r is the source-geophone distance, ro is a reference offset (may be outside the analysis window, set by point closest to source), and A, Ao are trace amplitudes. Alpha is the decay coefficient in nepers/m. At the reference offset, ro, the program samples the amplitude envelope with some uncertainty (Ao*B rather than Ao exactly). The linear fit is done after converting to decibels:
dB=20*log10[ (A*r)/(Ao*ro) ] = 20*alpha*(r-ro)*log10(e) + 20log10(B) = slope*(r-ro)+ intercept
where the slope and intercept are in dB/meter and dB respectively.
EXAMPLE:
bgar wave.seg 5.0 20.0 +1.78
File wave.seg will be analysed for amplitude decay in the interval 5 to 20 meters from the source. A gain recovery will be done with 1.78 dB/m (regardless of what the decay analysis shows). The decay analysis will still be written to the list file, and the decay Postscript plot will still be generated (showing the linear regression results).
bgarxxxx.seg
named according to convention (first 4char bgar, the next 4char are the first 4char of the input file name, suffix .seg)
standard output
produces a progress bar
bgarxxxx.lst
Echo check of input parameters and results of decay analysis.
bgar.ps
PostScript plot of amplitude decay (Decibels) versus range from the reference offset. The linear fit is plotted as a straight line, the measurements as points.
bhelp(1), bamp(1), bgaz(1), lsqufit(3)
no known bugs
Copyright © 2017 by Paul Michaels
This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
P. Michaels, PE. <pm@cgiss.boisestate.edu>