sprat.m

基于matlab的反演程序,用于地球物理勘探中射线追踪及偏移成像程序.

function q=sprat(A1,A2,f,t1,t2,fsmo)

% q=sprat(A1,A2,f,t1,t2,fsmo)
%
% SPRAT applies the spectral ratio method to estimate an apparent
% interval attenuation factor, q, between the traces (wavelets) 
% whose amplitude spectra are A1 and A2. Both spectra must be the
% same length, one sided, and described by the frequency vector f.
% Spectra are smoothed prior to ratioing with a boxcar of length
% fsmo. The log spectral ratio is plotted and the user enters a box
% with the mouse (as in the manner of a zoom with PLT) which 
% determines the frequency range for the least squares fit. The 
% best fit straight line is then determined and plotted and the
% apparent q is shown.
%  A1 ... amplitude spectrum at time t1
%  A2 ... amplitude spectrum at time t2
%  f ... frequency vector for A1 and A2
%  t1 ... time for spectrum A1
%  t2 ... time for spectrum A2
%  fsmo ... length (Hz) of a frequency smoother
%
% by G.F. Margrave, July 1991
%
% NOTE: It is illegal for you to use this software for a purpose other
% than non-profit education or research UNLESS you are employed by a CREWES
% Project sponsor. By using this software, you are agreeing to the terms
% detailed in this software's Matlab source file.
 
% BEGIN TERMS OF USE LICENSE
%
% This SOFTWARE is maintained by the CREWES Project at the Department
% of Geology and Geophysics of the University of Calgary, Calgary,
% Alberta, Canada.  The copyright and ownership is jointly held by 
% its author (identified above) and the CREWES Project.  The CREWES 
% project may be contacted via email at:  [e-mail]
% 
% The term 'SOFTWARE' refers to the Matlab source code, translations to
% any other computer language, or object code
%
% Terms of use of this SOFTWARE
%
% 1) Use of this SOFTWARE by any for-profit commercial organization is
%    expressly forbidden unless said organization is a CREWES Project
%    Sponsor.
%
% 2) A CREWES Project sponsor may use this SOFTWARE under the terms of the 
%    CREWES Project Sponsorship agreement.
%
% 3) A student or employee of a non-profit educational institution may 
%    use this SOFTWARE subject to the following terms and conditions:
%    - this SOFTWARE is for teaching or research purposes only.
%    - this SOFTWARE may be distributed to other students or researchers 
%      provided that these license terms are included.
%    - reselling the SOFTWARE, or including it or any portion of it, in any
%      software that will be resold is expressly forbidden.
%    - transfering the SOFTWARE in any form to a commercial firm or any 
%      other for-profit organization is expressly forbidden.
%
% END TERMS OF USE LICENSE

% first smooth the spectra
if(fsmo>0)
 A1=convz(A1,boxf(fsmo,f));
 A2=convz(A2,boxf(fsmo,f));
end
delt=t2-t1;
% now ratio them
 rat=log(A2./A1);
% plot the ratio
 plot(f,rat)
 grid;
 xlabel('frequency');
 ylabel('log ratio');
 text(.1,.05,'Select frequency range','sc');
% get the frequency range of the fit
[x1,y1]=ginput;
 while ~isempty(x1)
  fmin=min(x1);
  fmax=max(x1);
  if fmin==fmax, error(' Zero length frequency band chosen'),end
% fit the straight line
  infit=near(f,fmin,fmax);
  p=polyfit(f(infit),rat(infit),1);
  line=polyval(p,f(infit));
% determine interval Q
  q=-pi*delt/p(1);
% draw new graph
  plot(f,rat,f(infit),line,'+')
  grid;
  xlabel('frequency');
  ylabel('log ratio');
  text(.1,.05,sprintf(' q estimate = %g',q),'sc');
  text(.1,.00,'Select frequency range','sc');
  [x1,y1]=ginput;
end