afd_reflect.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 r=afd_reflect(velocity,clipn)
% AFD_REFLECT ... calculate the reflectivity from a velocity model
%
% r=afd_reflect(velocity,clipn)
% 
% AFD_REFLECT calculates the normal indicence reflectivity of an input
% velocity model for use with AFD_EXPLOAD.  
%
% velocity = velocity matrix
% clipn = the number of "bin layers" with which to remove from the
%       edge of velocity matrix in order to prevent artifacts from
%       the absorbing boundary conditions
%     = the suggested number is 5, but zero may also be chosen
% r = refelctivity calculated as .5*abs(gradient(log(velocity)))
%
% Carrie Youzwishen, April 1999
% completely rewritten by G.F. Margrave August 2000
%
% 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]
% 
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% 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
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% recalculate velocity for exploding reflector model (1 way travel time)

[nz,nx]=size(velocity);

[rx,rz]=gradient(log(velocity));

tmp=.5*sqrt(rx.^2+rz.^2);
clear rx rz

r=zeros(size(tmp));
r(clipn+1:nz-clipn,clipn+1:nx-clipn)=tmp(clipn+1:nz-clipn,clipn+1:nx-clipn);





%create reflectivity matrix
%vnew=zeros(nz+2,nx);
%r=zeros(nz,nx);

%vnew(2:nz+1,:) = 1/2*log(velocity);
%vnew(1,:)=vnew(2,:);
%vnew(nz+2,:)=vnew(nz+1,:);

%temp(:,:)=(vnew(3:nz+2,:) - vnew(1:nz,:))/2;
%r(clipn+1:nz-clipn,clipn+1:nx-clipn)=temp(clipn+1:nz-clipn,clipn+1:nx-clipn);