Use of Remote Sensing In Archaeological Research
December 5, 2000
This project is a partial requirement for ES 771, which is taught by
Dr. James Aber of Emporia State University, Emporia, Kansas.
Remote sensing techniques have proven to be very useful in the search for archaeological sites. Techniques such as aerial photography, color-infrared photography, thermal infrared multispectral scanning (TIMS), and radar imaging have successfully been used to locate potential archaeological sites and add questions to known sites. This project will focus on the applications of aerial photography to archaeological prospecting, and how aerial photography has aided in locating archaeological sites which would never have been discovered at ground-level.
AERIAL PHOTOGRAPHY USED IN ARCHAEOLOGICAL RESEARCH
Types of aerial photography commonly used for archaeological prospecting are black-and white film photography, color photography, and color-infrared photography. Black-and- white aerial photography records around twenty-two shades of gray in the visible spectrum, and is limited by atmospheric conditions such as cloud cover, haze, and must operate during daylight hours. Normal color photography records electromagnetic energy in the region from 0.4 to 0.7 um, and captures the terrain in the same colors as our eyes perceive the landscape. Color film has an advantage over black-and-white film in that crop color variations can be seen from the air. Color-infrared film records reflected energy in the region just below 0.3 um to just above 0.9 um, (ultraviolet to near-infrared energy) and the energy on the film is portrayed as false color (Jensen, 2000). CIR film is sensitive to slight variations in vegetation, and since archeological features can affect the plants that grow above them, these features can become visible in CIR photography (NASA Archeological Remote Sensing website).
Archaeological sites show up in aerial photos depending on their state of preservation, by light-shadow contrasts, differences in the soil, or by differences in height and color of cultivated crops (Aerial Archive website, University of Vienna). Color changes and faint lines visible from the air but invisible on the ground can be caused by buried cultural remains. These visual indicators are referred by aerial archaeologists as crop, soil, and shadow marks (GIS and Remote Sensing for Archaeology, Burgundy, France website).
CLick Here To View Examples of Aerial Archaeology
Cropmarks are formed by variations in the subsoil, which are caused by buried archaeological features that cause differential crop growth. As crops begin to ripen in early Summer, the walls, pits, and ditches of past settlements affect the rate at which crops change color and also affect the speed and height to which they grow. For example, crops growing over a buried ditch would be taller and larger, since the ditch contains additional moisture, compared to the soils around it, and are considered to be "positive" crop marks (Figure 1). Crops growing over the buried remains of a wall will tend to be smaller since the wall encourages water to drain away from the soil, and root growth could be interrupted, and these are considered to be "negative" crop marks (Figure 2). The appearance of cropmarks is enhanced by dry conditions, such as during times of drought, where differences in the ripening crop's condition can become very noticeable with aerial photography. Certain crops such as wheat, barley, and cereal crops produce especially good crop marks with good definition and resolution (Aerial Archaeology Research Group (AARG) website, 2000).
Figure 1. Positive Crop Marks (Source: GIS and Remote Sensing for Archaeology, Burgundy, France website).
Figure 2. Negative Crop Marks (Source: GIS and Remote Sensing for Archaeology, Burgundy, France website).
Soil marks are formed whenever a different soil is used to fill in a ditch or road, and this
"filler" soil is different enough in composition to distinctly contrast with the in-situ soil (Figure 3). Also, differences in soil moisture between the different soils also can aid in viewing the soil marks from an aerial perspective (Burgundy, France website).
Figure 3. Soil Marks (Source: GIS and Remote Sensing for Archaeology, Burgundy, France website).
Shadow marks are caused by small variations in topography, which create shadows early or late in the day (Burgundy, France website). This light-shadow contrast might not be discernable during
mid-day, but only when the sun angle is low (Aerial Archive, University of Vienna). Figure 4 illustrates this phenomena.
Figure 4. Pueblo She', Gallisteo Basin, New Mexico. Illustrating concept of shadow marks. This pueblo is only visible during dawn or sunset, when sun angle is low (Source: Aerial Archaeology Newsletter website, Photo: Tom Baker, 1996).
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