The ship is mirrored along a line just below the ‘Unity Line’ lettering on its hull. A red buoy is similarly miraged and appears to be hanging in the air. The true horizon is invisible having been replaced by miraged sky. The apparent very choppy ‘horizon’ is purely the lower edge of the mirage.
This ‘inferior mirage’ was produced by a lower layer of air heated by contact with the relatively warm Baltic at 6C overlain by much colder air at -2C.
Light passing at low angles across the layers is refracted so that rays from the ship’s hull appear to be coming upwards from beneath it. Our brain interprets that as a reflection from water.
The horizon and water line is missing. This is a 'vanishing-line' effect.
The ray diagram grossly exaggerates the vertical scale and ray curvature in order to portray the effects. Two rays from the upper hull (A) reach the eye. The upper one is slightly curved downwards towards the warmer air. The lower ray is sharply curved and appears to the eye to come from a reflection in the water. Rays from lower down (B) do the same. Position (C) is different. Only one ray reaches the eye. Rays from beneath (C) cannot reach the eye at all - that part of the hull and water is invisible.
The level (C) is the level of the mirage "vanishing-line". The 'real' view and inverted mirage view join at the vanishing line and the eye can see no details of the scene that are below it. The more distant the object, the higher is the vanishing line
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