Aerial Photo Analysis and Aerial Survey


Archaeologists have been using aerial prospecting and photography since just after World War One to locate buried structure, roads, and other features of ancient landscapes. Several archaeologists who served in that air war noticed strange circles and square patterns from the air that were not visible on the ground and that were not parts of the trenches or modern landscape. After the war they returned to these locations to find that these were actually archaeological sites, ancient roads, and other features of buried ancient landscapes. Early pioneers of 'aerial archaeology' conducted the first such surveys in Europe and the Middle East in the 1920's. Charles Lindbergh also conducted similar surveys in Central America in the 1930's.

Aircraft used in aerial survey and photography

How is it possible to see ancient landscapes and the buried remains of structures that can be a thousand years old?

Faint lines and color changes visible from the air are often invisible on the ground, and can be caused by buried cultural remains. Aerial archaeologists refer to these as crop, soil, and shadow marks. Crop marks form because there can be noticeable variations in crop vigor, color, or height when crops or natural vegetation grows over buried walls or other cultural remains. These are called 'negative' crop marks, as the crop is less vigorous due to the lack of moisture or root vigor caused by the buried walls. The opposite are 'positive' crop marks, where the crops are taller or more virorous when growing over pits or postholes. There is more moisture and better root growth, so the crops grow better. These differences are heightened in times of crop stress, such as a draught. In the major French draught of 1976 thousands of new archaeological sites were discovered from the air. Soil differences also can be visible, such as where a road or ditch was filled in with soil from a different place. These are called 'soil' marks. Small variations in topography causing shadows that are visible early or late in the day, these are called 'shadow' marks.

Research in the applications of various remote sensing techniques has been conducted in the Arroux valley area since 1978, with many of hours of survey flights being flown over the years at different times of the year, different times of day, using different films, etc. Aerial surveys and aerial photography have been conducted from low-flying aircraft and several important sites, roads, and other features have been discovered. Manual interpretation and photogrammetric analysis of existing vertical mapping photographs has also been conducted.

Gallo-Roman villa/Aerial view

This is a Gallo-Roman villa rustica, that was discovered by aerial survey in 1979. It is located in an area where Gallo-Roman era pottery were located in field surveys conducted in 1977, but the nature and extent of the site was not evident from the ground. Click on the image above for a larger picture. You can clearly see the outline of individual rooms in this large villa. The villa is a large (~100m on a side) farm community structure, with stone and cement walls. The walls are now about 60 cm below the current surface. Individual rooms served as living quarters, workshops, granaries, etc. The green square is probably the remains of a wooden structure associated with the villa. We can assume this because it is on the same axis as the main structure. It may have been a storage building or an animal pen, as the soil there is more fertile, causing better modern soil and therefore more crop growth. The curving patterns at bottom right are where a tractor with a disk plow drove over a pile of building stones from the villa that have been piled up by the farmers. The structure continues into the next field above, but is very difficult to see, given the different vegetation cover. This is a good example of the difficulty of locating such structures from the air.

Ground view

This is a ground view of the villa, taken the same day. If you know it is there, you can clearly see the geometric pattern of the negative crop marks on the ground, but the farmer who owned this land never suspected that he had an entire Roman era villa complex in this field. Large amounts of Roman roof tile and ceramics were surface collected. Unfortunately, this villa complex, the first discovered in the Arroux valley, was destroyed by a gravel mining operation over the following winter, just before we were to start our initial investigation of the site.

Here is an outline map and reconstruction of a similar villa rustica complex that has been discovered, excavated, and partially rebuilt. The site is in southern Germany, south of Stutgart. You can visit their website, including virtual tours of the villa, etc.

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Note the similarity of the corner tower outline and interior plans with the aerial photo of our villa complex above.

Many other structures, road segments, and other features in the region have been photographed from the air and are then marked on maps for entry into the GIS database. More recently, we have used GPS units in the air to better locate the features.


~ Welcome and Project Background ~ Remote Sensing and GIS ~ The Research Area ~ Aerial Photo Analysis and Aerial Prospecting ~ Airborne Thermal Scanning ~ Archival Aerial Photographs ~ Satellite Remote Sensing ~ GIS ~ GIS Line-of-sight Analysis ~ GIS Predictive Modeling ~ Historic Map Digitization ~ Visualization ~ Recent Project Activities ~ Future Directions ~ Hi Tech Digs TV Documentary ~ Acknowledgements ~ Bibliography ~ Weblinks ~ Contact Information ~

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