Aerial archaeology
Aerial prospection is one of the archaeological methods that only became possible in Saxony after reunification. It requires a very flexible use of a small sport airplane that is dependent on plant growth and weather conditions and can be planned at short notice. In the 1990s, Otto Braasch, the veteran expert in German aerial archaeology, took on this task for Saxony. In just a few years, he discovered more than 3,000 new sites and thus considerably expanded our knowledge of archaeological landscapes.
Since 2001, the State Office for Archaeology has been carrying out the photo flights itself. An ultralight aircraft is chartered for this purpose and the archaeologist, equipped with maps and cameras, goes in search of sites at an altitude of 300-400 meters. The objectives are the inspection and photographic recording of archaeological monuments visible above ground, the documentation of current large-scale excavations and the prospection of previously unknown sites. The aerial image archive of the Saxony State Office for Archaeology currently has more than 120,000 aerial images, which are available as color slides or black and white negatives for the older years, but have been available as digital images for more than 10 years.
Aerial prospection (exploration of as yet unknown monuments) is based on the fact that human intervention in the earth changes the soil structure. Where there are now backfilled ditches and pits, the soil stores slightly more water and provides good growing conditions for plants; where paths compact the soil or foundations create a stony subsoil, plant growth is inhibited. These small-scale differences in the growth cycle of the plants can be seen from the air as differences in color or height. The characteristics are particularly evident in annual plants, especially cereals, maize and beet, whereby the individual growth behavior of each plant behaves like the pixel of a digital image.
The characteristics of the vegetation are not the same every year, but depend on a variety of variable circumstances. These include, for example, the extent of frost stress on winter cereals and drought or moisture in the important growing months of April and May. Accordingly, the “drought years“ has recently led to exceptionally good results. In extremely dry conditions, the outlines of prehistoric buildings could be detected even in maize and even in grass – generally poor indicator plants.
In Saxony, aerial prospection can be used to document fortifications and moats or the course of historical paths very well. Today, leveled burial mounds or trapezoidal tombs are among the other common observations. Very good conditions are required for prehistoric house floor plans in which every single post is recognizable.
The flight route is recorded using GPS (Global Positioning System). On the one hand, this makes it easier to find certain monuments during the flight and, on the other hand, to localize the discovered and photographed vegetation features. The photos are georeferenced afterwards. This allows the findings to be reconciled with the map sheet. The photographed locations are precisely described in a database and a geographic information system (GIS). The archived data is used both for scientific purposes and to protect the recorded archaeological and historical sites. The targeted collection, evaluation and archiving of aerial photographs of known or previously unknown sites is part of the activities of Department 31, which is responsible for the inventory of monuments at the Saxon State Office for Archaeology. In ArchaeoSN, the aerial images can be used as overview images of the sites. They also help to classify a site in the landscape and show changes.
