The Center Members Education ScienceLabs

Archaeo- geophysics lab.Dept. of Physics, Sofia University, James Bourchier 5, Sofia 1164,

Bulgaria, YYShopov@phys.uni-sofia.bg,www.phys.uni-sofia.bg/bul/departments/ucsrt/agpl/

index.html

Dr. Yavor Shopov- supervisor

Members:Dr. Diana StoykovaDr. Ludmil Tsankov Dr. Milen TsekovValentin Vasilev

Introduction ArchaeologicalGeophysics lab of Department ofPhysics of Sofia University is theonly one in Bulgaria which developsnew geophysical methods and equipmentfor study of archaeological objectsand their dating (Shopov et al.,1993, Dermendjiev et al, 1996). Thislab has equipment and specialists forusing of broad range ofarchaeogeophysical methods. Here wedemonstrate possibilities of thesetechniques for solving of variousarchaeological tasks.

Archaeogeophysical MethodsThis lab uses followingarchaeogeophysical methods forexploration and non- destructiveinvestigation of archaeologicalobjects:I. Radar Methods 1. Ground penetrating radar (GPR) –

This method was developed by NASA tostudy the lunar ground. Introductionof these space technology toarchaeology makes GPR the mostpowerful archaeogeophysical technique

(Conyers, 2004), but interpretation ofGPR data is most complicated andrequires very complex data computing.It is the most complicated and complexarchaeogeophysical technique. GPRallows registration of so finearchaeological objects that are hardto see by eye and can be missed duringarchaeological excavations (Conyers,2004). Advantages: а. GPR is the only

archaeogeophysical method which allowspreparation of 2D slices (maps) ofunderground objects from variousdepths under the surface without theirexcavation (Conyers et al., 2004),(fig.1).b.It is the only archaeogeophysical

method which allows preparation of 3Dreconstructions of the precise shapesand depths of underground objects(Conyers et al., 2004), (fig.2).c.It allows precise determination of

depths of the underground objectsunder the surface.d.It allows visualization of the

underground objects as radar images inreal time during the measurements.

e.It allows simultaneousgeophysical exploration andarchaeological excavation of theregistered anomalies.

Fig.1. Amplitude Slice Map 100-150 cm. underthe surface demonstrating foundations of abuilding and a possible Roman water line (up)by (Conyers et al., 2004).

Fig.2. Three- Dimensional Rendered Surfaceof the foundations of the building on fig.1constructed from Amplitude Slice Maps likethis on fig.1 from various depths under thesurface. (Conyers et al., 2004). Even separatestones are visible.f.It has highest resolution from

all geophysical techniques. g.It can be used for scanning of

vertical walls and localization ofunhomogeneities in it.h.Registered signal can undergo

further computing for extraction ofinvisible details from the raw scanand graphic display of the results. i.It allows fast scanning of large

area. It is effective for large scale

exploration with high horizontalresolution.j.It allows connecting of different

archaeological excavations by GPRexploration of the space between them.k.GPR exploration can be done

through ice, asphalt, concrete etc.(Archaeological Geophysics labwebsite, 2007).l.On rough terrains can be done

step-by-step measurements which allowsdeeper penetration of the radarsignal. Disadvantages: а. Interpretation of

the signal is extremely complicated(Conyers, 2004) and requires years ofexperience of GPR studies ofarchaeological sites. b.Very high cost of the equipments. c.It can not be used in conductive

environment (like sea water) or saltysoils. d.Limited penetration depth which

depend on the soil humidity. Usuallyit varies from 1 meter in wet soil to17 m in buildings (ArchaeologicalGeophysics lab website, 2007)e.Archaeological applications of GPR

require an expert of very unusualtraining in specific fields ofgeophysics, geology and statisticalphysics. Experience in other GPRapplications can not be applied onarchaeological sites and experts onthem can not be easily trained inarchaeological applications of GPRGPR applications in archaeology

(Archaeological Geophysics labwebsite, 2007) are nondestructivelocalization and mapping of culturallayers in following buriedarchaeological objects:-tombs and burials -tunnels, catacombs, mud- huts and

underground channels-walls of buildings-fire places -metal and ceramic artifacts and

coatings-cavities and defects in buildings -caves, bunkers, caverns and karstic

futures

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-underground reservoirs and buriedpipes.Nondestructive stratification of: -sediments, river and lake

deposits;-soil layers including ancient

arable lands;-water table;-faults and land slides.Nondestructive study and monitoring

of archaeological objects, culturalheritage and undergroundcommunications.

Experimental partCalibration Experiments: Largenumbers of calibration experimentswere made inside the building ofDepartment of Physics of SofiaUniversity (fig.3) and surroundinggrounds with known undergroundcommunications (pipes, canals,tunnels, etc) before the start of thefield GPR measurements. Theydemonstrated that this equipmentworks perfectly on open ground andinside buildings and visualize allknown futures of the studied terrains(fig.3, 4). It can work 17 metersdeep in dry environment (fig.4). Thisdepth is 70 % deeper than the claimsof the producer of this GPR unit andantenna.

Fig.3. (up) Amplitude Slice Map of thereflection of the radar radiation from theconcrete bars on the ceiling of the 4-rd floormeasured on 35-62 cm depth through theconcrete foundation of the 5th floor, by Y.Shopov & D. Stoykova. Dimensions of X and Yaxis are in meters.(Down) Photo of the same concrete bars on theceiling of the 4-rd floor of building “B” of

Dept. of Physics of Sofia University scannedby GPR.

Fig.4. (up) Amplitude Slice Map of thereflection of the radar radiation from thetwo concrete bars supporting the ceiling ofthe basement measured on 17,11- 17,38 metersdepth from the 5th floor through five concretefoundations with total thickness of 3.25meters by Y. Shopov & D. Stoykova.(Down) Photo of the same concrete bars on theceiling of the basement (-1-st floor) ofbuilding “B” of Dept. of Physics of SofiaUniversity scanned by GPR.

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GPR measurements of Bulgarian archaeological sites. First GPR measurements on Bulgarian

archaeological site (fig.5) were madein 2007 in the tomb “GolyamataKosmatka“ (Shopov, in press). 60scans of the walls and floor of thetomb were measured with resolutionvarying from 1,3 to 1,7 cm. Fourgroups of 5 parallel scans each weremeasured on the walls of the tomb onheight from 0 to 250 cm. They weresummed in a 3D data base. Then it wassliced in 15 slices (fig.6) of 20nanoseconds (corresponding to athickness of 75 cm if the radar beampass through soil but to 3 m throughair)

Fig.5. Vertical Amplitude Slice Maps of theintensity of the radar radiation reflected byobjects around the tomb “GolyamataKosmatka“(fig.6) measured through the wall ofits round camera. (Up) A vertical slice 100-150cm behind the wall of the camera. External wallof another unknown round building isintersected In the middle of the scans.(Middle) A vertical slice 150-225 cm behind thewall of the camera. In the beginning and theend of the scans are intersected external wallsof the other round building. (Down) A verticalslice 450- 525 cm behind the wall of thecamera. In the beginning and the end of thescans are intersected external walls of theother round building. Three vertical structuresbetween them can be internal columns. Colorcodes of the intensity of the reflected radarradiation are given to the right. Obtained slices have resolution of

0.1 m. in horizontal, but 0.5m. invertical direction. Scanned tombcamera was round, so obtained slicesare segments of a circle (fig.6). Soobtained 2D maps looks as prints ofcylindrical seals (fig.5). Theydemonstrate that second unexcavatedcamera is located behind the west wallof the tomb. It is twice bigger thanthe camera in the excavated tomb.

Fig. 6. Scheme of the tomb, distribution ofthe radar radiation during its scanning andpositions of the 15 slices of 20 nanosecondseach (corresponding to a thickness of 75 cm ifthe radar beam passes through soil but to 3 mthrough air). It was unusually complicatedbecause all important scans are vertical due tothe great depth of the tomb, which makesimpossible to measure it from the surface ofthe mound by GPR .

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Fig. 7.А (up) A scan of the walls of thevestibule of the tomb 0- 50 сm above the floorsuggesting that the radar radiation penetratestrough homogeneous material et least 16 metersin all directions. Fig. 7.B (down) A scan ofthe walls of the vestibule of the tomb 200- 250сm above the floor. It demonstrates that theradar radiation penetrates through the granitewall of the tomb in the homogeneous soilfilling of the mound outside the tomb wall.

Scans of the walls of the tomb inthe lowest scanning position suggestthat the radar radiation penetratestrough homogeneous material (Fig. 7.А)at least 16 meters in all directions.Material of the walls is granite. Itmeans that the whole tomb is embeddedat least 50 centimeters deep in agranite square at least 35 meters indiameter. This does not mean that thesquare is circled. It can be extendedin all directions but radar radiationcan not reach its edges. The soilfilling of the mound is detectedthrough the granite wall of the tomb(Fig. 7.B) everywhere at over 50 cmabove the floor.

GPR measurements of prehistoric archaeological sites. Prehistoric sites are the mostdifficult archaeological objects forarchaeogeophysical survey due to lackof metal objects in them. Most of theartifacts have the same chemicalcomposition and physical properties asthe surrounding ground. Especiallystone artifacts have same propertiesas stones aground. So GPR is the mostappropriate archaeogeophysicaltechnique for survey of Neolithicsettlements (fig.8) and is the only

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one usable for survey of Paleolithicsites.

Fig.8. Amplitude Slice Map, 252– 261.5 cmunder the surface of an archeological site insouth Bulgaria demonstrating foundations of apossible stone wall (up) of a potentialNeolithic building measured by Y.Shopov, A.Petrova, D. Stoykova and V. Vasilev.Dimensions of X and Y axis are in meters. GPR is most suitable geophysical

technique for solving of most of thetasks of archaeological exploration.Before its development it wasconsidered impossible to locateunderground objects like plastic,terracotta, concrete and asphalt. GPRbecame the main technique forlocalizing and mapping of non-conductive, non-metal and non-magnetic objects. It can be used evenfor exploration of under-waterobjects in fresh water basins(Archaeological Geophysics labwebsite, 2007).Therefore in the lastyears it is the main focus of work ofArchaeological Geophysics lab ofSofia University.

II. Electrical resistivity methods. 2. Electrical profiling. It

measures profiles of the electricresistivity (fig.9). It alloweddeepest geophysical exploration of aBulgarian archaeological site at 19meters below the surface (Shopov,2007) but such measurements can bedone even on 40 m. depth. It is mostappropriate for searching of tombs,caves, tunnels or bunkers. 3. Vertical Electrical Probing-

detects the same objects aselectrical profiling serving fordetermination of the depth of thedetected anomalies. 4. Electrical tomography

(continuous electrical probing)-allows visualization of anomalies of

the electric resistivity and of theobjects creating it.Although its great depth of

operation these methods are extremelyslow, laborious and expensive, havemany limitations and interferences. Sonow Archaeological Geophysics lababandons these methods except ofVertical Electrical Probing whichsometimes can help GPR fordetermination of the depth of thedetected anomalies.

Fig.9 Map of the electric resistivity ofOmurtag tomb. Vertical axis is in units ofOmh/m. (Shopov, 2007)

III. Induction methods- usemilitary technologies for location ofmines.5. Pulse induction- Allows

localization of large metal objects ondepth up to 6 meters. Its equipmentemits powerful electromagnetic pulsesand measures the inducted current inthe underground objects between thepulses (Aittoniemi et al., 1986). Itworks through walls and stones. Itallows very fast scanning and highprecession of localization of theobjects, but it doesn’t allow precisedetermination of the depth of theanomalies. Underground cables, rebaror metal nets mask objects and makeimpossible its use.

6. Electromagnetic Induction- Allowsprecise localization of small metalobjects and determination of the metalbuilding them by its conductivity(Gardiner, 1967). Works on shallowdepth which varies from 0.3 up to 1

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meter depending on the size of thefound object. Its equipment emitselectromagnetic field and measuresthe inducted current in theunderground objects passing betweenits coils. It doesn’t allowdetermination of the depth of theanomalies. Underground cables, rebaror metal nets mask objects and makeimpossible its use.Due to the limitations of each

method in some cases is necessary touse several methods and apparatus tosolve a specific task.

All geophysical explorations are non-destructive and harmless for the archeologicalobjects unlike of the coring which damage theobject in some degree.

Acknowledgements. We express specialthanks to V. Mutafov, A. Koichev andM. Purvin for their help in theterrain measurements, to Dr. D.Gergova, G. Kitov and K. Leshtakovfor the helpful data, discussions andproviding of technical support ontheir excavation sites. We thank toHydroloc Ltd. for providing of theirequipment for field research. Wethank to prof. G. Tenchov for thediscussions.

References:.Aittoniemi et al. (1986) US

Pattent 4,605,898, 7p..Archaeological Geophysics lab

website, (2007) www.phys.uni-sofia.bg/bul/departments/ucsrt/agpl/index.html.Conyers L. B. (2004) Ground-

penetrating radar for archaeology. Altamirapress, Oxford, 201p..Dermendjiev V., Shopov Y. Y.,

Buyukliev G. N. (1996) High-Precision Method of Cave DepositsDating and an Implication for

Archeometric Study. - Physical andChemical Techniques (PACT) Journal, 45, IV.7,pp. 307-312.Gardiner F. G. (1967) US Pattent 3,

355,658, 4p..Kitov G., Purvin M., Shopov Y. Y.

(2008) GPR exploration of the moundGolyamata Kosmatka near Shipkavillage. Archeological findings and excavations(AOR) for 2007., pp.291-292 (inBulgarian).Shopov Y. Y, Dermendjiev V,

Buyukliev G. (1993) A New Method forDating of Natural Materials withPeriodical Macrostructure. B. Patent51012 from v.8 1, 1990, Patent officebulletin, 1993, 1, p.20-21 (inBulgarian).Shopov Y. Y. (2007) Electrical

profiling of the Omurtag tomb.- Avant-garde Research of Ancient Bulgarians, v.1, pp.57-58; Archeological findings and excavations(AOR) for 2006. (in Bulgarian).Shopov Y. Y., (2008) Potential and

limitations of the Archaeogeophysicaltechniques: in “Along the Path of thePast”- Jubilee book in honour of 65-thanniversary of Dr.George Kitov. Editedby D.Dimitrova, IK Aros pp. 204-209 .Shopov Y., Diana Stoykova, A.

Petrova, Valentin Vasilev, LudmilTsankov (2008) Potential andlimitations of the archaeo-geophysicaltechniques. - Geoarchaeology andArchaeomineralogy (Eds. R. I. Kostov,B. Gaydarska, M. Gurova). Proceedingsof the International Conference, 29-30October 2008 Sofia, Publishing House“St. Ivan Rilski”, Sofia, pp. 320-324..Shopov Y. Y. (2009) The secret of

the success of Dr. Georgi Kitov. AviTohol, v.31, pp.3-4 (in Bulgarian)

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