Evaluating visibility at sea: Instrumental data and historical nautical records. Mount Etna from the Calabrian Ionian coast (Italy)

Visibility has an encompassing importance in humans' perception of the landscape, since the first encounter with a new environment normally occurs through sight. In historical and archaeological studies, two main methods (i.e., the geometric method and the Geographical Information System [GIS] computation) have been employed to determine the distance from which an object can be recognized. However, neither is exhaustive when applied to a maritime context, where the main factor affecting the visibility radius is weather. To establish how far at sea an object can be seen, and how its visibility would have changed in different weather conditions, we adopted a method from Aerosol Optics based on a well-established mathematical model of the light scattering phenomena. We applied this method to compute the visibility radius in historical studies. To demonstrate its application, we choose to examine the visibility of a key point in both historical and current seafaring, namely Mount Etna (Sicily, Italy), from the Ionian coast of Calabria (Italy). The results obtained by the application of this method have been validated by comparing them with mentions of Mount Etna in both written sources and on-the-ground records.