function plot_drifters(info, dirs)

% read dimensions
d       = xb_read_dims;
t       = [50 100 150 450];

% read output
xbo1    = xs_peel(xb_read_output(pwd, 'vars', {'zs' 'u' 'v'}, 'index', t));
xbo2    = xs_peel(xb_read_output(pwd, 'vars', 'drifter*'));

% read drifters
c       = struct2cell(xbo2);

% plot output
fh = figure;
sx = ceil(sqrt(length(t)));
sy = ceil(length(t)/sx);
for i = 1:length(t)
    subplot(sy,sx,i); hold on;
    
    pcolor(d.x,d.y,squeeze(xbo1.zs(i,:,:)));
    quiver(d.x,d.y,squeeze(xbo1.u (i,:,:)),squeeze(xbo1.v(i,:,:)),1,'w');

    for ic = 3:length(c)
        x = c{ic}(1:t(i),1); x(x<0) = nan;
        y = c{ic}(1:t(i),2); y(y<0) = nan;
        plot(x, y, '-ok', 'MarkerFaceColor', 'g', 'MarkerEdgeColor', 'k');
    end
    
    shading interp;
    axis equal;
    box on;
    
    title(sprintf('t = %ds', t(i)));
end

xb_write_plot(fh, dirs.output, 'fig1');