nx=100;ny=120;
x=[1:1:nx];
y=[1:1:ny];
v=ones(ny,nx);
S=[10 20;80 80];
t = fast_fd_2d(x,y,v,S);

dt=t(:,:,1)+t(:,:,2);
dt=dt-min(dt(:));
F = munk_fresnel_2d(1,dt);
subplot(1,3,1);imagesc(x,y,t(:,:,1));axis image;title('Source')
subplot(1,3,2);imagesc(x,y,t(:,:,2));axis image;title('Receiver')
subplot(1,3,3);imagesc(x,y,F);axis image;title('Fresnel')