minwave.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 [wavelet,twave]=minwave(ampspec,f,stab)

% [wavelet,twave]=minwave(ampspec,f,stab)
% [wavelet,twave]=minwave(ampspec,f) 
%
% Given an input amplitude spectrum, minwave computes the 
% corresponding minimum phase wavelet in the time domain.
% ampspec= the input amplitude spectrum. Must be positive definite 
%           everywhere if stab is zero.
% f= frequency coordinate vector
% stab= stab factor. if stab is non-zero (and positive) then 
%       ampspec(f) is altered to ampspec(f)+stab*Max(ampspec)
%       (default is zero)
% SUGGESTION: create an appropriate f using fftrl. f must be
% a frequency vector from 0 th Nyquist of length 1 greater than
% a power of two. Ampspec must be the same length. 
% 
% by G.F. Margrave, May 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

 if(nargin==2)
   stab=0.0;
 end
% test for stab condition
 if(stab>0.0)
  	ampstab=stab*max(ampspec);
 else
    ampstab=0.0;
 end
 
% modify spectrum
 ampspec=ampspec+ampstab;
 
%% pad to a power of 2
% a2=padpow2(ampspec);
% if(length(a2)~=length(ampspec))
% 	ind=find(a2==0.0);
% 	a2(ind)=ampstab*ones(size(ind));
% 	ampspec=a2;
% 	f=xcoord(f(1),f(2)-f(1),ampspec);
%end
 
% test for stability
 if(min(ampspec)<=0.0)
	  error('Amplitude spectrum not positive definite')
 end
% 
%
% construct the complex symmetric spectrum
  L1=1:length(ampspec);L2=length(ampspec)-1:-1:2;
  symspec=[ampspec(L1) conj(ampspec(L2))];
  cmpxspec=log(symspec)+i*zeros(size(symspec));
% do the hilbert transform
  cmpxspec=hilbm(cmpxspec);
% cmpxspec=exp(cmpxspec);
  cmpxspec=exp(conj(cmpxspec));
  cmpxspec=cmpxspec-mean(cmpxspec);
% inverse fft
  wavelet=real(ifft(cmpxspec));
% time coordinates
  dt=1./(2.*f(length(f)));
  twave=0.:dt:(length(wavelet)-1)*dt;