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ifkmig.m
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ifkmig.m
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function [seismig,tmig,xmig]=fkmig(seis,t,x,v,params)
% FKMIG: Stolt's fk migration
%
% [seismig,tmig,xmig]=fkmig(seis,t,x,v,params)
%
% FKMIG performs post stack migration in the frequency wavenumber domain
% using the constant velocity method of Stolt (Geophysics 1978)
%
% seis ... matrix of zero offset data. One trace per column.
% t ... if a scalar, this is the time sample rate in SECONDS.
% If a vector, it gives the time coordinates for the rows of
% seis.
% x ... if a scalar, this is the spatial sample rate (in units
% consistent with the velocity information. If a vector, then
% it gives the x coordinates of the columns of seis
% v ... a scalar giving the constant velocity to migrate with
% params ... vector of migration parameters
% params(1) ... maximum frequency (Hz) to migrate
% ***** default = .6*fnyquist *********
% params(2) ... width of cosine taper (Hz) to apply above params(1)
% ***** default = .2*(fnyquist-params(1)) ********
% params(3) ... maximum dip (degrees) to migrate
% ***** default = 80 degrees *****
% params(4) ... width of cosine dip taper (degrees)
% ***** default = 90-params(3) degrees *****
% params(5) ... size of zero pad in time (seconds)
% ***** default = min([.5*tmax, tmax/cos(params(3))]) ******
% params(6) ... size of zero pad in space (length units)
% ***** default = min([.5*xmax, xmax*sin(params(3))]) ******
% params(7) ... if 1, zero pads are removed, if 0 they are retained
% ***** default = 1 *****
% params(8) ... if 0, use nearest neighbor interpolation
% if 1, use sinc function
% if 2, use spline function
% if 3, use linear interpolation
% ***** default = 1 *****
% params(9) ... if 1, apply cos(theta) wt factor.
% if 0, don't apply it
% ******* default = 1 *******
% params(10) ... number of points in sinc function interpolator. Must be
% an even number.
% ******* default = 8 ******
% params(11) ... number of locations in sinc function table.
% ******* default = 25 ******
% params(12) ... if 1 use faster fk transforms
% if 0, use slower, memory conserving, transforms
% ******* default = 0 ******
% params(13) ... =n means print a message as every n'th wavenumber
% is migrated.
% ******* default = 50 ******
% seismig ... the output migrated time section
% tmig ... t coordinates of migrated data
% xmig ... x coordinates of migrated data
%
% G.F. Margrave and J. Bancroft, CREWES Project, U of Calgary, 1996
%
% 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: [email protected]
%
% 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
tstart=clock; % save start time
%totflops=flops;
[nsamp,ntr]=size(seis);
if(length(t)>1)
if(length(t)~=nsamp)
error('Incorrect time specification')
end
dt=t(2)-t(1);
else
dt=t;
t=((0:nsamp-1)*dt)';
end
if(length(x)>1)
if(length(x)~=ntr)
error('Incorrect x specification')
end
dx=x(2)-x(1);
else
dx=x;
x=(0:ntr-1)*dx;
end
fnyq=1/(2*dt);
% knyq=1/(2*dx);
tmax=t(nsamp);
xmax=abs(x(ntr)-x(1));
%examine parameters
nparams=13;% number of defined parameters
if(nargin<5); params= nan*ones(1,nparams); end
if(length(params)<nparams)
params = [params nan*ones(1,nparams-length(params))];
end
%assign parameter defaults
if( isnan(params(1)) ); fmax= .6*fnyq;
else fmax = params(1); if(fmax>fnyq); fmax=fnyq; end
end
if( isnan(params(2)) ); fwid = .2*(fnyq-fmax);
else fwid = params(2);
if( (fmax+fwid)>fnyq ); fwid = fnyq-fmax; end
end
if( isnan(params(3)) ); dipmax = 85;
else dipmax = params(3); if(dipmax>90); dipmax=90; end
end
if( isnan(params(4)) ); dipwid = 90-dipmax;
else dipwid = params(4);
if((dipwid+dipmax)>90); dipwid= 90-dipmax; end
end
if( isnan(params(5)) ); tpad= min([.5*tmax abs(tmax/cos(pi*dipmax/180))]);
else tpad = params(5);
end
if( isnan(params(6)) ); xpad= min([.5*xmax xmax*sin(pi*dipmax/180)]);
else xpad = params(6);
end
if( isnan(params(7)) ); padflag= 1;
else padflag = params(7);
end
if( isnan(params(8)) ); intflag= 1;
else intflag = params(8);
end
if( isnan(params(9)) ); cosflag= 1;
else cosflag = params(9);
end
if( isnan(params(10)) ); lsinc= 8;
else lsinc = params(10);
end
if( isnan(params(11)) ); ntable= 25;
else ntable = params(11);
end
if( isnan(params(12)) ); mcflag= 0;
else mcflag = params(12);
end
if( isnan(params(13)) ); kpflag= 50;
else kpflag = params(13);
end
%apply pads
%tpad
nsampnew = round((tmax+tpad)/dt+1);
nsampnew = 2^nextpow2(nsampnew);
%tmaxnew = (nsampnew-1)*dt; %erreur dans le code, cette ligne assumait que le
%temps commençait à zero!
tmaxnew = t(1) + (nsampnew-1)*dt;
tnew = t(1):dt:tmaxnew;
ntpad = nsampnew-nsamp;
seis = [seis;zeros(ntpad,ntr)];
%xpad
ntrnew = round((xmax+xpad)/dx+1);
ntrnew = 2^nextpow2(ntrnew);
xmaxnew = (ntrnew-1)*dx+x(1);
xnew = x(1):dx:xmaxnew;
nxpad = ntrnew-ntr;
seis = [seis zeros(nsampnew,nxpad)];
disp([' tpad = ' int2str(ntpad) ' samples']);
disp([' xpad = ' int2str(nxpad) ' traces']);
%forward f-k transform
disp('forward f-k transform')
if(mcflag)
[fkspec,f,kx] = fktran(seis,tnew,xnew,nsampnew,ntrnew,0,0);
else
[fkspec,f,kx] = fktran_mc(seis,tnew,xnew,nsampnew,ntrnew,0,0);
end
clear seis; %free space
df=f(2)-f(1);
nf=length(f);
%compute frequency mask
ifmaxmig = round((fmax+fwid)/df+1);
pct = 100*(fwid/(fmax+fwid));
fmask = [mwhalf(ifmaxmig,pct); zeros(nf-ifmaxmig,1)];
fmaxmig = (ifmaxmig-1)*df; %i.e. fmax+fwid to nearest sample
%now loop over wavenumbers
ve = v/2; %exploding reflector velocity
dkz= df/ve;
kz = ((0:length(f)-1)*dkz)';
kz2=kz.^2;
th1= dipmax*pi/180;
th2= (dipmax+dipwid)*pi/180;
if(th1==th2)
disp('no dip filtering');
end
zip= zeros(size(f));
disp([int2str(length(kx)) ' wavenumbers to migrate']);
for j=1:length(kx)
%evanescent cutoff
fmin = abs(kx(j))*ve;
ifmin = ceil(fmin/df+1);
%compute dip mask
if(th1~=th2)
ifbeg=max([ifmin 2]);%first physical frequency excluding dc
ifuse = ifbeg:ifmaxmig; %frequencies to migrate
if(length(ifuse)==1)%special case
dipmask=zeros(size(f));
dipmask(ifuse)=1;
else
%theta=asin(fmin./f(ifuse)); % physical dips for each frequency
if1 = round(fmin/(sin(th1)*df))+1; % sample number to begin ramp
if1=max([if1 ifbeg]);
if1=min([if1 nf]);
if2 = round(fmin/(sin(th2)*df))+1; % sample number to end ramp
if2=max([if2 ifbeg]);
dipmask=zip; % initialize mask to zeros
if(~isempty(ifuse))
dipmask(if1:nf)=ones(size(if1:nf)); % pass these dips
if(if2<if1)
dipmask(if2:if1) = .5+.5*...
cos(pi*((if2:if1)-if1)/(if2-if1));
%cos((theta((if2:if1)-ifbeg+1)-th1)*pi/(th2-th1));
end
end
end
else
dipmask=ones(size(f));
end
% apply masks
tmp=fkspec(:,j).*fmask.*dipmask;
%compute f's which map to kz
fmap = ve*sqrt(-kx(j)^2 + kz2);
% fmap contains one value for each kz giving the frequency
% which must map there to migrate the data. Of course many
% of these frequencies will be far too high.
ind=find(fmap<=fmaxmig);
%
% ind is a vector of indicies into fmap which gives will
% always start at 1 and end at the highest f which is to be
% migrated
%now map samples by interpolation
fkspec(:,j) = zip; %initialize output spectrum to zero
if( ~isempty(ind) )
%compute cosine scale factor
if(cosflag)
if( fmap(ind(1))==0)
scl=ones(size(ind));
li=length(ind);
scl(2:li)=ve*kz(ind(2:li))./fmap(ind(2:li));
else
scl=ve*kz(ind)./fmap(ind);
end
else
scl=ones(size(ind));
end
if(intflag==1)
%complex sinc interpolation
fkspec(ind,j) = scl.*csinci(tmp,f,fmap(ind),[lsinc,ntable]);
elseif(intflag==0)
% nearest neighbor interpolation
ifmap = round(fmap(ind)/df+1);
fkspec(ind,j) = scl.*tmp(ifmap);
elseif(intflag==2)
% spline interpolation
% ifmap = (fmap(ind)/df+1);
fkspec(ind,j) = scl.*interp1(f,tmp,fmap(ind),'spline');
elseif(intflag==3)
% complex linear interpolation
fkspec(ind,j)=scl.*clinint(f,tmp,fmap(ind));
end
end
if( floor(j/kpflag)*kpflag == j)
disp(['finished wavenumber ' int2str(j)]);
end
end
%remove NaNs is fkspec
for i=1:size(fkspec,1)
for j=1:size(fkspec,2)
if isnan(real(fkspec(i,j)))==1
fkspec(i,j)=0;
end
end
end
%inverse transform
disp('inverse f-k transform')
if(mcflag)
[seismig,tmig,xmig]=ifktran(fkspec,f,kx);
else
[seismig,tmig,xmig]=ifktran_mc(fkspec,f,kx);
end
%remove pad if desired
if(padflag)
seismig=seismig(1:nsamp,1:ntr);
tmig=tmig(1:nsamp);
xmig=xmig(1:ntr);
end
tend=etime(clock,tstart);
disp(['Total elapsed time ' num2str(tend)])
%totflops= flops-totflops;
%disp(['Total floating point operations ' num2str(totflops)])