Updated images.

docs/source/gprmodelling.rst

@@ -29,7 +29,7 @@ temporal :math:`\Delta t` steps play a very significant role -- since the smalle
 
 .. _yeecell3D:
 
-.. figure:: images/yeecell3D.png
+.. figure:: images/yeecell3d.png
     :width: 500px
 
     Single FDTD Yee cell showing electric (red) and magnetic (green) field components for 3D transverse electromagnetic (TEM) mode.
@@ -40,7 +40,7 @@ gprMax is fundamentally based on solving Maxwell's equations in 3D using the FDT
 
 .. _yeecell2DTMz:
 
-.. figure:: images/yeecell-blank.png
+.. figure:: images/yeecell2dTMz.png
     :width: 500px
 
     Single FDTD Yee cell showing electric (red), magnetic (green), and zeroed out (grey) field components for 2D transverse magnetic (TM) z-direction mode.