Laboratories of the University Center for Space Research and Technologies
Supervisor: Dr. Yavor Shopov
The Archaeological Geophysics laboratory of Department of Physics of Sofia University is the only one in Bulgaria which develops new geophysical methods and equipment for study of archaeological objects and their dating. This lab has equipment and specialists for using of broad range of archaeogeophysical methods. Here we demonstrate possibilities of these techniques for solving of various archaeological tasks.
The lab uses following archaeo-geophysical methods for exploration and non-destructive investigation of archaeological objects.
- Radar Methods
- Ground penetrating radar (GPR) - this method was developed by NASA to study the lunar ground. Introduction of these space technology to archaeology makes GPR the most powerful archaeogeophysical technique (Conyers, 2004), but interpretation of GPR data is most complicated and requires very complex data computing. It is the most complicated and complex archaeogeophysical technique. GPR allows registration of so fine archaeological objects that are hard to see by eye and can be missed during archaeological excavations (Conyers, 2004).
- Electrical resistivity methods
- Electrical profiling - measures profiles of the electric resistivity. It allowed deepest geophysical exploration of a Bulgarian archaeological site at 19 meters below the surface (Shopov, 2007) but such measurements can be done even on 40m. depth. It is most appropriate for searching of tombs, caves, tunnels or bunkers.
- Vertical electrical probing - detects the same objects as electrical profiling serving for determination of the depth of the detected anomalies.
- Electrical tomography (continuous electrical probing) - allows visualization of anomalies of the electric resistivity and of the objects creating it.
- Induction methods
- Pulse induction - allows localization of large metal objects on depth up to 6 meters. Its equipment emits powerful electromagnetic pulses and measures the inducted current in the underground objects between the pulses (Aittoniemi et al., 1986). It works through walls and stones. It allows very fast scanning and high precession of localization of the objects, but it doesn’t allow precise determination of the depth of the anomalies. Underground cables, rebar or metal nets mask objects and make impossible its use.
- Electromagnetic induction - allows precise localization of small metal objects and determination of the metal building them by its conductivity (Gardiner, 1967). Works on shallow depth which varies from 0.3 up to 1 meter depending on the size of the found object. Its equipment emits electromagnetic field and measures the inducted current in the underground objects passing between its coils. It doesn’t allow determination of the depth of the anomalies. Underground cables, rebar or metal nets mask objects and make impossible its use.
The laboratory uses methods and equipment developed at the Physics Department. They are subject to three Bulgarian inventions, and one Canadian patent of our laboratory’s team. Some of the devices developed, and used by the laboratory have no analogues abroad, others are subject to numerous attempts of coping or modifing by other laboratories around the world.
The laboratory was created in 2001. In 2005 and 2006, a PhD student from the University of Bologna, Italy was trained for six months here within the European exchange program ERASMUS.
Scientific Fields and Experiments
- Study of global climate changes in the past - the team of our laboratory developed an indirect index of insolation, which is obtained from measurements of the distribution of the luminescence of the organic acids in flowstone calcites along the growth axis of their crystals. Absolute dating of these calcites allows measurement records of insolation in the last 250,000 years. So far these are the only experimental records of insolation. They are widely used in studies of global climate change in the past.
- Study of regional climate changes - study of regional climate changes using flowstone calcites as natural climatic stations. For this purpose, the laboratory has developed indirect indices of annual temperature and annual rainfall, which are obtained from measurements of the distribution of the luminescence of the organic acids in flowstone calcites.
- Using luminescence for search, field and laboratory diagnostics of minerals, oil and gas - includes (a) a development of a new method, techniques, and apparatus for registration of luminescence of minerals and its spectrum in the field conditions and (b) a research on the spectra of the luminescence of the minerals in the laboratory.
- Studies of records of contamination and migration of toxic metals and of groundwater acidity - the luminescence of some samples flowstone calcite is induced by toxic elements. Some of them even have annual zonality due to variations in the acidity of the groundwater, which causes variations in the solubility of some toxic elements such as uranium, lead, etc.
- Dating of fluorescent records - the apparent annual cyclicity of records allows calculating the average annual growth rate of the flowstone by determining the average annual period (in pixels) using time series analysis. This procedure was set at the base of a fundamentally new dating method called "Autocalibration dating."