July09 = rectify_surface(2009,7,'w');
December09 = rectify_surface(2009,12,'w');

close all
figure
subplot(2,1,1)
pcolor(July09.xi,July09.yi,July09.zi);
shading interp
colorbar
axis tight
title('Reference plot')

subplot(2,1,2)
pcolor(July09.xi,July09.yi,(December09.zi-July09.zi));
shading interp
caxis([-0.5 0.5])
colorbar
axis tight
title('Difference plot')