qfilter.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 trout= qfilter(trin,t,q,delt,fmin,fmax)

% trout=qfilter(trin,t,q,delt,fmin,fmax)
% trout=qfilter(trin,t,q,delt,fmin)
% trout=qfilter(trin,t,q,delt)
% trout=qfilter(trin,t,q)
%
% QFILTER uses the SPIN algorithm (Margrave 1989) to apply a
% bandlimited constant Q (forward) filter to the input trace.
% The bandlimitation is a numerical requirement (which should not
% be pushed too much past .8*Nyquist) and is implemented as a 
% stationary minimum phase filter superimposed on the qfilter.
% To guard against temporal wraparound, a considerable time pad
% is required. The input trace is automatically lengthened to the
% next power of 2, however, if a larger pad is needed, it should
% be done externally. The output trace will have the same length
% as the original length of trin.
%
% trin= input trace
% t= input time coordinate for trin
% q= desired Q factor
% delt= temporal sample rate for the time variant q spectrum
%       ********** default=.05 sec ************
% fmin= minimum frequency to pass without minimum phase bandpass
%       attenuation 
%      ******** default= 10 ******* 
% fmax= maximum frequency to pass without minimum phase bandpass 
%       attenuation
%      ******** default= .6*Nyquist ******* 
% trout= output trace with forward qfilter applied
%
% 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
 
% Set defaults
  if nargin < 6
    fmax=.6/(2.*(t(2)-t(1)));
  end
  if nargin < 5
    fmin=10;
  end
  if nargin < 4
    delt=.05;
  end
% force input to be a column vector
  trin=trin(:);
  t=t(:);
% find first nonzero amplitude for later rescaling
  indicies=find(abs(trin)>0);
  imin=min(indicies);
% pad the input trace
  ntrout=length(trin);
  trin=padpow2(trin);
  dt=t(2)-t(1);
  t=xcoord(t(1),dt,trin);
% generate the time variant spectrum
  fnyq=1./(2*dt);
  f=linspace(0.,fnyq,length(trin)/2+1);
  [tvsq,tq]=tvsqf(delt,f,q,fmin,fmax);
% apply the qfilter
  fwidth=1./(2*(tq(2)-tq(1)));
  trout=tvfilt(trin,t,tvsq,tq,f,fwidth,fmin,fmax);
% use an mwindow to select the first ntrout samples
  mw=mwindow(2*ntrout-1);
  trout=trout(1:ntrout).*mw(ntrout:length(mw));
% normalize the result by equalizing the power of the first
%  10% of the live samples
  lnorm=round(ntrout*.1);
  a=norm(trin(imin:imin+lnorm),2);
  b=norm(trout(imin:imin+lnorm),2);
  trout=trout*(a/b);