gusucode.com > DSISoft是由加拿大地质调查局发布的用于垂直地震剖面(VSP)数据处理的免费软件包 > dsisoftv3/dsisoftv3/dsisoftv3/main/trim.m
function [dataout]=trim(datain,t1,t2,tmax)
%[dataout]=trim(datain,t1,t2,tmax)
%
%Trim Statics
%Used to align traces in time by making small adjustments.
%
%T1 and T2 are the start and end of the time window that will be used to
%align the traces. A trace representing the sum of all traces in the
%record will be created within this time window and this summed trace
%will be cross correlated with each trace in the same time window.
%
%tmax is the maximum time shift that will be allowed i.e. it cross
%correlateion lag times will only be allowed between (tmax) and (-tmax)
%and a maximum will be found between these lag times.
%
%Time shifts will be stored in trace header word 25.
%
%Convention: positive value = shift traces down
% negative value = shift traces up
%
%Successive applications of this module will improve final trace alignment.
%Similar to INSIGHT module 'trim'.
%
%DSI customized VSP processing software
%written by Kristen Beaty November, 1997
%$Id: trim.m,v 3.0 2000/06/13 19:22:26 gilles Exp $
%$Log: trim.m,v $
%Revision 3.0 2000/06/13 19:22:26 gilles
%Release 3
%
%Revision 2.0 1999/05/21 18:46:54 mah
%Release 2
%
%Revision 1.1 1999/01/06 19:09:10 kay
%Initial revision
%
%
%Copyright (C) 1998 Seismology and Electromagnetic Section/
%Continental Geosciences Division/Geological Survey of Canada
%
%This library is free software; you can redistribute it and/or
%modify it under the terms of the GNU Library General Public
%License as published by the Free Software Foundation; either
%version 2 of the License, or (at your option) any later version.
%
%This library is distributed in the hope that it will be useful,
%but WITHOUT ANY WARRANTY; without even the implied warranty of
%MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
%Library General Public License for more details.
%
%You should have received a copy of the GNU Library General Public
%License along with this library; if not, write to the
%Free Software Foundation, Inc., 59 Temple Place - Suite 330,
%Boston, MA 02111-1307, USA.
%
%DSI Consortium
%Continental Geosciences Division
%Geological Survey of Canada
%615 Booth St.
%Ottawa, Ontario
%K1A 0E9
%
%email: dsi@cg.nrcan.gc.ca
disp('[dataout]=trim(datain,t1,t2,tmax)');
dataout=datain;
nrec=datain.fh{12}; %get number of records
int=datain.fh{8}; %sampling interval (sec)
tstart=datain.fh{9}; %start time (sec)
samples=datain.fh{7}; %number of points per trace
%find index values of t1, t2 and tmax
t1=round((t1-tstart)./int)+1;
t2=round((t2-tstart)./int)+1;
tmax=ceil((tmax)./int);
for COUNT=1:nrec %loop over records
ntpr=datain.th{COUNT}(12,1); %number of traces this record
dataout.dat{COUNT}(:,:)=0; %initialize dataout.dat
subdata=datain.dat{COUNT}(t1:t2,:); %make subset of data
for tr=1:ntpr %loop over traces
baseline=mean(subdata(:,tr));
subdata(:,tr)=subdata(:,tr)-baseline; %each trace must have mean value of 0
end %loop over traces
pilot=sum(subdata,2); %make pilot trace
pilot=pilot-mean(pilot); %must have mean of 0 for cross correlation
%find the cross correlation function in the Fourier domain
% tic;
[shift_f]=xcor_f(pilot,subdata,tmax);
% disp('Fourier domain solution')
% toc;
%using Fourier solution because it gives same solution in less time
%now find the cross correlation function in the time domain
% tic;
% [shift_t]=xcor_t(pilot,subdata,tmax);
% disp('time domain solution')
% toc;
shift=shift_f;
%put shift times into trace headers
dataout.th{COUNT}(25,:)=dataout.th{COUNT}(25,:)+shift(1,:).*int;
for t=1:ntpr %loop over number of traces
index=abs(shift(1,t));
if shift(1,t)==0 %no shift
dataout.dat{COUNT}(:,t)=datain.dat{COUNT}(:,t);
elseif shift(1,t)<0 %shift upwards
dataout.dat{COUNT}(1:(samples-index),t)=datain.dat{COUNT}(index+1:samples,t);
else %shift downwards
dataout.dat{COUNT}(index+1:samples,t)=datain.dat{COUNT}(1:(samples-index),t);
end %if
end %loop over number of traces
end %loop over records
%end of function trim
%------------------------------------------------------------------------
function [shift]=xcor_t(pilot,data,tmax)
%returns the shift in units of number of indexes that the data needs to
%be moved by for trim statics
%performs cross correlation in the time domain
l=length(pilot);
n=tmax;
self=pilot;
pilot=[zeros(size(1:n)),pilot',zeros(size(1:n))];
pilot=pilot';
%perform autocorrelation on pilot trace
for k = 0:2*n
ac(k+1,1) = sum(self(1:l,1).*pilot(1+k:l+k,1));
end %for k = 0:2*n
[junk,ac_max]=max(ac(:,1)); %find index of the peak of autocorrelation
%perform cross correlation
for tr=size(data,2):-1:1 %loop over traces
for k = 0:2*n
cc(k+1,tr) = sum(data(1:l,tr).*pilot(1+k:l+k,1));
end %for k = 0:2*n
[junk,cc_max]=max(cc(:,tr)); %find index of peak of cross correlation
shift(tr)=cc_max-ac_max; %find shift (in indexes)
end %loop over traces
%end of function xcor_t
%------------------------------------------------------------------------
function [shift]=xcor_f(pilot,data,tmax)
%returns the shift in units of number of indexes that the data needs to
%be moved by for trim statics
%performs cross correlation in the Fourier domain
%
%flips data traces upside down, then multiplies the magnitudes and adds
%the phases of the pilot and data traces in the Fourier domain
if tmax>length(pilot)/2
error('tmax must be less than half of size of time window')
end
self=pilot;
pilot=[zeros(size(1:tmax)),pilot',zeros(size(1:tmax))];
pilot=pilot';
fpoints=2^nextpow2(length(pilot)); %number of points to be used in fft
%take fft of flipped pilot before zero padding to use for autocorrelation
au_fft=fft(flipud(self),fpoints);
data=flipud(data); %flip data traces upside down
pilot_fft=fft(pilot,fpoints);
sub_fft=fft(data,fpoints);
%multiply magnitudes and add phases to get cross correlation function fft
pfabs=abs(pilot_fft);
pfang=angle(pilot_fft);
for tr=1:size(data,2) %loop over traces
mag(:,tr)=abs(sub_fft(:,tr)).*pfabs;
phase(:,tr)=angle(sub_fft(:,tr))+pfang;
end %loop over traces
xcor_fft=mag.*exp(phase.*i); %convert to complex
xcor=ifft(xcor_fft,fpoints); %perform inverse fft to return to time domain
%perform autocorrelation
mag=abs(au_fft).*pfabs;
phase=angle(au_fft)+pfang;
aucorr_fft=mag.*exp(phase.*i); %convert to complex
aucorr=ifft(aucorr_fft,fpoints); %inverse fft
aucorr=fftshift(aucorr); %unwrap autocorrelation
[junk,ac_max]=max(aucorr); %find peak within window
k=1;
for t=-tmax:tmax
if ac_max+t>size(xcor,1)
row(k)=ac_max+t-size(xcor,1);
elseif ac_max+t<1
row(k)=ac_max+t+size(xcor,1);
else
row(k)=ac_max+t;
end %if/else
k=k+1;
end %for t=-tmax:tmax
for tr=1:size(data,2)
xcor(:,tr)=fftshift(xcor(:,tr)); %unwrap correlation
%only consider shifts of <+-tmax
sub_xcor(:,tr)=real(xcor(row,tr));
[junk,xcor_max]=max(sub_xcor(:,tr)); %find index of peak of cross correlation
shift(tr)=xcor_max-tmax-1; %find trim shift in indexes
end %loop over traces
%end of function xcor_f