Archaeologists use new methods to research antiquity
The Airborne Laser Scanning (ALS) method, which scans terrain precisely and contact-free for mapping purposes and then shows it as a 3D model – is providing archaeologists with entirely new findings in connection with ancient sites. The journal "PNAS" contains a report on the use of the new remote sensing technique in the ancient city of Jerash, in Jordan, written by archaeologist Prof. Achim Lichtenberger from the University of Münster and his Danish colleague Prof. Rubina Raja from the University of Aarhus. This ALS technique, which is highly promising for archaeology, primarily facilitates new findings in reconstructing the conditions existent in urban areas of antiquity which were not only densely populated, but which also developed rapidly.
In their work, the researchers worked together with geoscientists David Stott and Søren Munch Kristiansen, superimposing the aerial laser-scan images of the Jordanian excavation site onto historical aerial photographs, the oldest of which dates back to 1917. This enabled them to compare topographical peculiarities and changes and to project the ancient remains onto a precise model of the terrain. "It’s a bit like turning back the clock. We discovered aqueducts on the images, for instance, which had been unknown up to now. Thanks to ALS, we can say today for example where and how water supplies were managed in antiquity."
What is novel about the method is the linking-up of several sources and the data relating to them: on the one hand, aerial photographs dating from World War One; on the other, the modern 3D laser scanning, accurate to within a few millimetres; and, in addition, data from scattered archaeological excavations. "This makes it possible to draw up a very precise map of an entire ancient city", says the archaeologist.
Jerash was considered to be especially suitable for ALS because it was an area of economic and social life which enjoyed strong and rapid growth. "An additional factor is that for many centuries between late antiquity and the modern age the area was only very sparsely populated, if at all", says Lichtenberger. The consequence of this was that large parts of the ancient city were initially preserved from destruction or from having building work carried out on top of them. At the same time, however, archaeological features there bearing testimony to antiquity threatened to be lost as a result of the urban expansion which has occurred in the last few decades.
The new mapping method is part of a Danish-German research undertaking – the "Jerash Northwest Quarter Project", in which excavation work began in 2011. It is largely being funded by the German Research Foundation (DFG) and the Danish Carlsberg Foundation.
Achim Lichtenberger and his colleagues are hoping for a new impetus from the ALS method as regards excavations planned for the future and dealing with cultural heritage sites all over the world, because, in many parts of the world, population growth and climate change represent an acute risk for such sites. "Often it is a race against the clock", says Lichtenberger, "to document and understand life in earlier societies before the historical remains are irreversibly destroyed."
Original publication in the journal "PNAS":
"One hundred years of remote sensing and urban sprawl: Multi-temporal, multi-sensor mapping of a historic city in the Middle East"; DOI 10.1073/pnas.1721509115