Miraged Ships in the Straight of Juan de Fuca just south of the entrance to Victoria Harbour, British Columbia, Canada imaged by Craig Clements (gallery). Images ©Craig Clements, shown with permission.
   
An inverted ship sails above the lower vessel. The lower picture has parts of a third upright ship above the inverted one! These are 'superior' mirages - superior because the images are above the miraged object.   The Fata Morgana is an extreme superior mirage.   More everyday 'inferior' or hot road mirages have the image below the object creating them.

Craig comments, "It was an unusually hot day in July and a very distinct temperature inversion formed between the colder water and warm atmosphere."   The inversion layer, colder air below warmer, is the key to the mirages. The lower air is visible as the dark band.

Light rays passing between the dense colder air and the upper warm air are refracted so that ray paths become curved and concave to the horizon level.    I.e. they tend to curve downward. The ray curvature is strongest where the vertical temperature gradient is greatest.

In the diagram (below) the ray 'b' from the ship mast is slightly curved making the mast appear to be at a point above the 'real' ship. Ray 'c' from the hull encounters a higher region of even greater temperature gradient and is more strongly refracted. Where ray crossing occurs the resulting image is inverted - an upside down ship sails above the lower one.

When the inversion layer is thick enough, rays from the mast have a third route 'd' through upper warmer air towards the eye or camera. They form a third image - this time the right way up. Traces of it show in the second picture where the hull is doubled and parts of superstructure appear just below the dark band boundary..