event_diph.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 amat=event_diph(amat,t,x,v,x0,x1,z0,theta,amp,flag,noversamp)
% EVENT_DIPH: construct a dipping event by diffraction superposition
%
% amat=event_diph(amat,t,x,v,x0,x1,z0,theta,amp,flag,noversamp)
%
% EVENT_DIPH inserts a dipping (linear) event in a matrix. The event
% is constructed from a superposition of hyperbolae.
%
% amat ... the matrix of size nrows by ncols
% t ... vector of length nrows giving the matrix t coordinates
% x ... vector of length ncols giving the matrix x coordinates
% v ... velocity (scalar)
% x0 ... starting x coordinate of the event
% x1 ... ending x coordinate of the event
% z0 ... starting depth of the event
% theta ... dip (degrees) of the event
% amp ... vector of length 2 giving the amplitudes at either end
%	of the event. Intermediate amplitudes are interpolated in x.
% flag ... if 1, then amplitudes are divided by cos(theta)
%				otherwise no effect
%      ******** default = 1 *********
% noversamp ... each output trace is created by nearest-neighbor interpolation into
%		a temporary over-sampled trace that is then properly resampled. The greater the
%		oversampling, the better the result.
%      ******** default = 10 *********
%
% G.F. Margrave, CREWES, 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]
% 
% 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<11) noversamp=10; end
if(nargin<10) flag=1; end

%loop over columns
%nc= between(xlims(1),xlims(2),x,2);
[nr,nc]=size(amat);

v=v/2;

if(length(amp)==1) amp=[amp amp]; end

%determine the origins of the hyperbolae
ind=between(x0,x1,x,2);
if(x0>x1) ind=fliplr(ind); end
if(~ind) error('check x coordinates'); end
xnot=zeros(size(ind));znot=xnot;tnot=xnot;
xnot(1)=x(ind(1));znot(1)=z0;tnot(1)=znot(1)/v;
dx=sign(x1-x0)*(x(2)-x(1));
for k=2:length(ind)
	xnot(k)=x(ind(k));
	znot(k)=znot(k-1)+dx*tan(pi*theta/180);
	tnot(k)=znot(k)/v;
end	

%interpolate new locations
%this is inefficient but who cares
dxnew=dx*cos(pi*theta/180);
xnew=xnot(1):dxnew:xnot(end);
znew=interp1(xnot,znot,xnew);

xnot=xnew;
znot=znew;
tnot=znot/v;	

anot=amp(1)+(xnot-x0)*(amp(2)-amp(1))/(x1-x0);

tmin=t(1);
tmax=t(length(t));
dt=t(2)-t(1);
dt2=dt/noversamp;
ttmp=tmin:dt2:tmax;

costheta=1;
if(flag==1) costheta=cos(pi*theta/180); end

for k=1:nc %loop over traces
	trctmp=zeros(size(ttmp))';
	tk=sqrt(tnot.^2+((x(k)-xnot)/v).^2);
	ak=anot.*tnot.*(tk.^(-1.5));
	ind2=between(tmin,tmax,tk);
	if(ind2~=0)
		ik=round(tk(ind2)/dt2)+1;
		for kh=1:length(ik)
			trctmp(ik(kh))=trctmp(ik(kh))+ak(ind2(kh));
		end
	
		%amat(:,k)=amat(:,k) + resamp(trctmp,ttmp,dt);
		amat(:,k)=amat(:,k) + resample(trctmp,1,noversamp)/costheta;
	end
end