Changing temperature gradients cause the horizon to move up and down behind the 7 mtr light tower on Aylmer Island(4.5 km). Cold air pools over night bending light toward the earth to create an image of other wise unseen ice surface.

A casual observer could easily miss the whole effect which amounts to a movement of 6 minutes. The obsessive observer can get a winters entertainment watching,photographing and modelling the effect

The dip of the horizon for a given height of eye (7.8 mtr)is a classic problem. The result of refraction is represented by considering light to travel in a straight line over and earth of a slightly increase radius(15% larger). In a constant gradient all objects at a given distance experience exactly the same refraction so there is no magnification or distortion. Every part of the image of a specific object is displaced the same amount.

In general the temperature gradient near the surface is far from constant.The animation represents the more typical case where the bottom of the an objects is lifted more than the top; giving a highly squashed image of the fishing hut. The temperature gradient must be decreasing rapidly within the 3 mtr height of the hut located at 8.5 km.