Mirage & eye height

 

The recent cold outbreak has produced striking mirages on the Lake. The water being above freezing and the air being well below produces a large temperature gradient in the lowest few centimetres of air and a more gentle one a bit above. This is an ideal setup to give an inferior mirage, and they abound. 

The Harrop cable ferry appears as an inferior mirage as seen from Kokanee Creek Park. The distance is 4.5 km and the intervening water is too rough to give a simple reflection. The appearance of the mirage depends upon the height of the eye above the lake’s surface, which for this picture is about two metres. The water upon which the ferry sits and the bottom of the hull have vanished only to be replaced by an inverted image of the upper portions of the ferry.

When the eye level is lowered to a metre above the lake’s surface, only the superstructure is seen, both right way up and upside down. (In the intervening time the ferry moved across the narrows.) If the eye is moved within a few centimetres of the lake’s surface, the whole ferry vanishes.

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One Response to Mirage & eye height

  1. Claire says:

    How fascinating.

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