function refsection(seis,beg,dt,aflag,color,delta,lf,hf,tshift);

% REFSECTION(SEIS,BEG,DT,AFLAG,DELTA,LF,HF,TSHIFT) plots a seismogram section
% of seismograms in 2D array SEIS. BEG is begin time of section, DT is sample
% interval and AFLAG determines amplitude scaling. If AFLAG < 0 each trace is
% scaled to its maximum amplitude, if AFLAG = 0 each trace is scaled to the
% maximum amplitude of the entire section, and if AFLAG > 0 then each trace is
% scaled to that amplitude (note this option allows direct comparison of plots
% produced by different calls to SECTION). COLOR controls the color of the
% record section (e.g., 'k' for black). DELTA is and array containing the
% position of the geophones (can be left empty []). LF and HF are low and high
% cutoff frequencies for bandpass filtering (no filtering is applied if they
% are left blank). TSHIFT is a time shift that is be applied to the entire
% section (no time shift is applied is TSHIFT=0 or []).
% S.R. 1/20/08
 
ny=size(seis,1);
nt=size(seis,2);
if nargin < 4
  aflag=-1;
  color='k';
  delta=[];
  lf=[];
  hf=[];
  tshift=0;
end
if isempty(tshift)
   tshift=0;
end

if isempty(delta)
  delta=[1:ny];
end

ddelta=min(delta-[0 delta(1:end-1)]);

% precondition seis
for iy=1:ny
    seis(iy,:)=seis(iy,:)-mean(seis(iy,:));
    seis(iy,:)=detrend(seis(iy,:));
    seis(iy,:)=taper(seis(iy,:),0.001,dt,0.0011,nt*dt-0.0011);
end
if ~isempty(lf)
    seis=bpfilt(seis,dt,lf,hf);
end
if (tshift~=0)
    seis=ttshift(seis,dt,tshift);
    if tshift>0
       seis=taper(seis,0.001,dt,tshift+0.001,-1);
    else
       seis=taper(seis,0.001,dt,-1,nt*dt+tshift-0.001);
    end
end
for iy=1:ny
    seis(iy,:)=seis(iy,:)-mean(seis(iy,:));
    seis(iy,:)=detrend(seis(iy,:));
    seis(iy,:)=taper(seis(iy,:),0.001,dt,0.0011,nt*dt-0.0011);
end

yaxe=[1:ny];
if aflag < 0
  for iy=1:ny
    xymat(iy,:)=delta(iy)-ddelta*seis(iy,:)/max(abs(seis(iy,:))+0.0000001);
    cxymat(iy,:)=delta(iy)-ddelta*( (sign(seis(iy,:))+1)/2 ) .* seis(iy,:) /max(abs(seis(iy,:))+0.0000001);
  end
elseif aflag == 0
  for iy=1:ny
    xymat(iy,:)=delta(iy)-ddelta*seis(iy,:)/max(max(abs(seis))+0.0000001);
    cxymat(iy,:)=delta(iy)-ddelta*( (sign(seis(iy,:))+1)/2 ) .* seis(iy,:) /max(max(abs(seis))+0.0000001);
  end
else
  for iy=1:ny
    xymat(iy,:)=delta(iy)-ddelta*seis(iy,:)/aflag;
    cxymat(iy,:)=delta(iy)-ddelta*( (sign(seis(iy,:))+1)/2 ) .* seis(iy,:) /aflag;
  end
end
time=[0:nt-1]*dt+beg;
plot(xymat,time,[color,'-']);
hold on
for iy=1:ny
  hh=fill(cxymat(iy,:),time,color);
  set(hh,'LineStyle','none')
  set(hh,'EdgeColor',[1 1 1])
end
hold off
ylabel('Time [seconds]')
xlabel('Distance [meters]')