Rendering Ghost Ships and Other Phenomena in Arctic Atmospheres

Abstract

The unique characteristics of the arctic atmosphere make for very interesting effects that cannot be seen anywhere else in the planet. The extremely cold temperatures, along with the existence of inversion layers in the temperature gradients, make the medium highly inhomogeneous. Its properties, including the index of refraction that rules the behavior of light, are no longer constant. As a consequence, light rays get bent while traversing the atmosphere, and the result is some spectacular phenomena; several examples are the arctic mirages (that have probably given rise to numerous ghost ship legends), the Fata Morgana or the Novaya-Zemlya effect. We present here an implementation of a ray tracer that can render all these effects, thus depicting phenomena never ray-traced before, as far as the authors know. We first build an accurate temperature profile for the arctic atmosphere, based on experimental data, then calculate the curved paths of the light rays as the index of refraction changes as a function of temperature, by solving the physically-based differential equation that describes their trajectory. The scenes are modelled using real data for the Earth and Sun dimensions and relative distance, thus maintaining accuracy in the results obtained.