Ground fog, also known as radiation fog or valley fog, is a type of fog that occurs in low-lying areas during calm and clear nights. It is caused by the cooling of the air close to the ground, resulting in the condensation of water vapor and the formation of a thick mist that hovers close to the surface. Some synonyms for ground fog include dew fog, pond fog, valley mist, low-lying cloud, and sea smoke. These terms are used to describe the same weather phenomenon, but differ in their geographic or contextual connotations. Regardless of the name used, ground fog can make for a picturesque and eerie landscape, especially in woodland or rural settings.