First Break Picker

Gambar di bawah ini merupakan First Break Picks yang dilakukan secara otomatis.Input merupakan data seismic shot gather dengan format ASCII. Lihat artikel ini (Matlab) atau ini (Perl) untuk melakukan konversi segy ke ASCII.

 

 

Berikut kode Matlab untuk First Break Picking:

%%% Automatic First Break Picker

%%% Agus Abdullah, PhD

clear; clc

load testfb.sgy.txt

trace=testfb_sgy';  % row=samples; cols: traces no.

ntrace=2000; % no of trace

tmax=2000; % time max

sr=4; % sampling rate

gt=0.06;% gradient threshold.  clean data: use small;  noisy: use high

bp=20;  % bad picks rejection threshold(ms). low: more agressive to remove bad picks.

sm=0.1; % smoothing trend. clean data: low; noisy data:high. to save near offset picks use low.

h = waitbar(0,'predicting first break...(1/3)');

for k=1:ntrace

waitbar(k/ntrace);

y=max(trace(:,k),0);

maxy=max(y);

y=y./maxy;

gg=gradient(y);

gg=min(gg,gt);

index=find(gg==gt,1);

zz(k)=isempty(index);

if zz(k) < 1

fb(k)=(index*sr);

else

fb(k)=0;

end

end

close(h)

fbs=smooth([1:ntrace],fb,sm,'rloess');

delta=abs(fbs-fb');

h = waitbar(0,'evaluating first break...(2/3)');

for i=1:ntrace

    waitbar(i/ntrace);

if delta(i)< bp

    fb(i)=fb(i);

else

    fb(i)=NaN;

end

end

close(h)

h = waitbar(0,'plotting...(3/3)');

for k=1:ntrace

    waitbar(k/ntrace);

plot(5*k+trace(:,k),[0:sr:tmax],'k');flipy; hold on

plot(5*k+trace(1,k),fb(k),'*r'); hold on

xlabel('trace #*5')

ylabel('time(ms)')

end

close(h)

clear; clc