Shadow marks (shadow relief) are a form of

archaeological Archaeology or archeology is the scientific study of human activity through the recovery and analysis of material culture. The archaeological record consists of artifacts, architecture, biofacts or ecofacts, sites, and cultural landscap ...

feature visible from the air. Unlike

cropmarks Cropmarks or crop marks are a means through which sub-surface archaeological, natural and recent features may be visible from the air or a vantage point on higher ground or a temporary platform. Such marks, along with parch marks, soil marks an ...

frost marks Frost is a thin layer of ice on a solid surface, which forms from water vapor in an above-freezing atmosphere coming in contact with a solid surface whose temperature is below freezing, and resulting in a phase change from water vapor (a gas) ...

and

soil mark Soil marks are differences in soil colour as a result of archaeological features. They can be seen when a ploughed-out earthwork has left hard dry material of a former bank and damper wetter material from a former ditch. They can also occur when ...

s they require upstanding features to work and are therefore more commonly seen in the context of extant sites rather than previously undiscovered buried ones. They are caused by the differences in height on the ground produced by archaeological remains. In the case of ancient, eroded

earthworks Earthworks may refer to: Construction *Earthworks (archaeology), human-made constructions that modify the land contour * Earthworks (engineering), civil engineering works created by moving or processing quantities of soil *Earthworks (military), m ...

these differences are often small and they are most apparent when viewed from the air, when the sun is low in the sky. This causes long shadows to be cast by the higher features, which are illuminated from one side by the sun, with dark shadows marking hollows and depressions. Artificial shadow marks can be created easily by constructing a virtual model of a site by merging aerial images (

Photogrammetry Photogrammetry is the science and technology of obtaining reliable information about physical objects and the environment through the process of recording, measuring and interpreting photographic images and patterns of electromagnetic radiant ima ...

) and then vectoring in a virtual light source from any direction and at any angle.

References

Methods in archaeology Archaeological features {{Archaeology-stub

See also

References