Study of Erbil Al-Qala citadel time changes by comparison of historical and contemporary image data

The Erbil Al-Qala citadel is located on a distinct hill (“tell”) in the foothills north of Iraq, in Kurdistan. The citadel is a historical city centre of presently rapidly growing Erbil, which is the capital city of the autonomous region of Kurdistan. The citadel has been inscribed on the World Heritage List since 21 June 2014. The Erbil citadel dates back thousands of years to the first settlers of Erbil. The resulting shape is a large, oval hill, and is properly referred to as a “tell”, which means a large mound created by many generation buildings one on top of another. There are historical aerial photographs of Erbil citadel made by Bradford in 1951. These unique images are taken as a stereoscopic image pair configuration. A digital model and historical orthophoto has been created from this data set. A basic map of the citadel has been created based on modern VHR satellite data and field measurements. Bradford’s historical images were processed in Agisoft PhotoScan software. Satellite images taken by Ikonos (2003), QuickBird (2005) and Pleiades (2014) satellites represent the second data sets. The created orthophotos and digital models of the citadel were mutually compared. The result is a map of missing objects that were destroyed during the second half of the twentieth century. Results based on image data processing from a long-term project of the CTU in Prague dealing with Kurdish historical monuments represent the main content of the proposed article