Digital photogrammetry for the documentation of structural damage in earthen archaeological sites: The case of Ajina Tepa, Tajikistan

Ajina Tepa is one of the most important archaeological sites in central Asia and it was fully excavated in the 1960s using modern documentation techniques. The UNESCO/Japan Trust Fund project ‘Preservation of the Buddhist Monastery of Ajina Tepa, Tajikistan’ started in 2005 and will be completed in 2008. Scientific documentation being one of the project aims, three-dimensional mapping of the walls and geomorphological mapping of the whole site were carried out. Digital stereo-photogrammetric techniques were applied to record the surface morphology of the earthen walls. At present, the walls are heavily eroded, especially when compared with their outlines as recorded in the 1960s. The top parts of the damaged walls are rounded and the basal parts typically show the erosion pattern known as coving. Rain and wind cause decay of the top parts and have created their rounded shape. At the bottom of the walls, erosion is caused by salt attack in combination with abrasion from wind and windblown silt. When the walls lose strength under their own load, the upper and middle parts of the walls may collapse suddenly. Digital photogrammetric techniques are extremely useful for documenting such phenomenon and in determining the shape of the walls before collapse. It is shown here that such a monitoring system supplies the basic data which enables measures to be taken to prevent collapse.