A technique of photographic observation and survey of the ground from an aircraft, spacecraft, or satellite which provides detailed information about sites and features without excavation. It is most important for locating archaeological sites before destruction of the landscape through building, road construction, or modern agricultural practices. When viewed from the air, sites may be revealed as crop marks, soil marks, shadow marks, or frost marks. For example, the plan of a site, ditches, walls, pits, etc. can be reflected in the way the crops grew (crop marks) or a pattern of dark occupation soil may show against a lighter topsoil or stone from walls may be just under the surface (soil marks). Oblique aerial photos, from lower altitudes, detect shadows created by earthworks and permit more detailed interpretations of known sites (shadow marks). Variations in the amount of frost retained on the ground may indicate the presence of buried archaeological features (frost marks). Though these can sometimes be recognized on the ground by careful fieldwalking and contour planning, much larger areas can be examined from the air and overall patterns will be clearer. The same site may not be susceptible every year to aerial photographs, as local climatic variation affects the nature of the feature fillings; a site may only be seen once in ten or twenty years. The use of false-color infrared photography has increased the versatility of aerial photography and the development of photogrammetry allows the accurate mapping of both archaeological and geographical information. Recording of thermographic and radar images complements photographic methods. Aerial photography has proved to be one of the most successful methods of discovering archaeological sites. Large areas of ground can be covered quickly, and the ground plan of a new site can be plotted from the photographs. Features can be revealed in extraordinary detail by these means. The pioneers of this technique were O.G.S. Crawford and Major Allen in Britain and Père Poidebard in Syria, though its first use goes back to 1906 at Stonehenge.