geosciences

Article Applications of Geophysical Surveys for Archaeological Studies in Urban and Rural Areas in Czech Republic and Armenia

Jaroslav Bárta 1,*, Tomáš Belov 1, Jan Frolík 2 and Jaroslav Jirk ˚u 1

1 G IMPULS Praha Ltd., J. Nerudy 232, 252 61 Jenec, Czech Republic; [email protected] (T.B.); [email protected] (J.J.) 2 Institute of Archaeology of the CAS, Prague, Letenska 123/4, 118 01 Praha, Czech Republic; [email protected] * Correspondence: [email protected]; Tel.: +420-724-066-550



Received: 8 August 2020; Accepted: 1 September 2020; Published: 5 September 2020


Abstract: The authors of the presented paper tested the possible use of geophysical methods in the field of archaeological and constructional-historical research. It focused on the historical center of Prague, where we took measurements in the built-up areas covered by cobble stones and asphalt. The works were carried out mainly at the Old Town Square, HradˇcanySquare, Charles Square and Lesser Town Square. Field conditions were completely different at the Armenia sites (intact agricultural areas). We used the methods of shallow geophysical survey, namely geoelectrical methods, gravimetry, seismics and magnetometry. Measurement results from the built-up areas were affected by presence of engineering networks, transportation and field obstacles. Working in the rural areas is generally less demanding in terms of implementation and evaluation, but our results show that proper selection of geophysical methods brings positive results even in urban areas. The research proved that good results can be expected if one uses multiple geophysical methods measuring various physical properties of an environment. The application of only one, albeit sophisticated method, is usually not enough. There is a necessity to improve interpretational software for the purposes of archaeological object detection. The objects are mainly buried within the first meters and are relatively small. Contrast of physical properties between searched objects and their surrounding environment does exist but typically is small and, therefore, it is necessary to measure multiple physical parameters simultaneously. The presented projects aimed not only to archaeology, but the results also had practical outputs for public administration and development.

Keywords: near surface geophysics; shallow geophysical survey; archaeology; interpretation; urban area; rural area; COST Action SAGA (CA17131)

1. Introduction This paper deals with using a set of geophysical methods for archaeological or constructional- historical research (for examples of the cooperation between both disciplines, see Frolík [1] and Reynolds [2]). Geophysical methods in archaeology have being carried out widely for decades (Conyers [3], Deiana [4], Gad Ej-Oedy [5] and Oswin [6]). The electrical resistivity tomography (ERT) method in archaeology shows (Ekincy [7]) who uses the 3D display of ERT results. Another possible method may be the ground penetrating radar (GPR), like in (Beresneva [8]). The success rate of routinely carried out magnetometry in archaeology is evaluated in (Almutari [9]). Brion [10] compares geophysical data with archaeological conclusions with respect to spatial analysis. For successful use of geophysics in archaeology, it needs to be based on the deeper theoretical basics of geophysical methods—one

Geosciences 2020, 10, 356; doi:10.3390/geosciences10090356 www.mdpi.com/journal/geosciences Geosciences 2020, 10, x FOR PEER REVIEW 2 of 26 geophysical methods—one cannot rely only on the superficial manuals of the geophysical instruments’ manufacturers to operate an instrument. Currently, the very topical issue of shallow seismic reflection is described in detail in Baker [11]. The basics of geophysical methods in the level of current knowledge are described by Butler [12] and Everett [13].

The authorsGeosciences of2020 the, 10 presented, 356 paper state the findings use of geophysical methods2 at of 26four squares in the historical downtown of Prague and at historically important sites in Armenia (Armavir province). Whilecannot rely the only Armenian on the superficial sites manuals were placed of the geophysical in country instruments’ areas manufacturers with practically to operate no buildings, transportationan instrument. nor engineering Currently, thenetworks, very topical the issue Prague of shallow sites seismic are coveredreflection is with described cobblestones in detail and are affected by instrong Baker [transportation11]. The basics of geophysicaland underground methods in theengineering level of current networks knowledge (cables, are described pipelines by , etc.). Butler [12] and Everett [13]. The resultsThe of authors the of Armenianthe presented paper and state Pragu the findingse research use of geophysical works weremethods presented at four squares as separate presentationsin the(described historical downtown in detail) of Prague within and the at historically SAGA importantWorksh sitesop inPrague Armenia-Czech (Armavir Republic province). (2019) and more detail Whilecan be the found Armenian in sitesthe werepresentations placed in country of Barta areas with[14], practically Barta [15] no buildings,and Jirku transportation [16]. nor engineering networks, the Prague sites are covered with cobblestones and are affected by strong The maintransportation goal of and the underground works in engineeringthe Prague networks center (cables, was pipelines, bringing etc.). findings via non-destructive methods, workingThe results not of only the Armenian for one and particular Prague research piece works of werearchaeological presented as separate research presentations, but to make an information(described database in detail)for other within city the SAGA development Workshop Prague-Czech-related activities, Republic (2019) i.e., andrevitalization more detail can of be free spaces, mapping outfound historically in the presentations valuable of Barta sections [14], Barta that [15 should] and Jirku not [16]. be destroyed via building activities in The main goal of the works in the Prague center was bringing findings via non-destructive methods, future, etc. Theworking Armenia not only works for one aimed particular mainly piece of to archaeological optimize the research, projects but, toleading make an to information documentation and preservationdatabase of archaeolog for other cityically development-related important sites activities, which i.e., are revitalization currently of endangered free spaces, mapping by an on-going industrializationout historically and vivid valuable housing sections development. that should not Thanks be destroyed to extensive via building field activities measurements in future, etc. , extensive The Armenia works aimed mainly to optimize the projects, leading to documentation and preservation experience wasof archaeologically gained, which important allowed sites whichevaluation are currently of multiple endangered geophysical by an on-going techniques industrialization in various field conditions andand vividgetting housing a picture development. of pros Thanks and to cons extensive of these field measurements, techniques. extensive experience was gained, which allowed evaluation of multiple geophysical techniques in various field conditions and 2. Materialsgetting and Methods a picture of pros and cons of these techniques. 2. Materials and Methods 2.1. Study Areas 2.1. Study Areas In Prague Infour Prague main four large main largesquares squares in inthe the historical historical center center were were chosen chosen (Figure 1().Figure All sites 1) are. All sites are characterizedcharacterized by a strong by a transpor strong transportationtation and and business business and and touristic touristic activities. activities.

Figure 1. FigureThe historical 1. The historical center center of ofPrague Prague with position position of studied of studied areas (squares). areas (squares).

2.1.1. Charles Square (Karlovo Náměstí) The main goal of the works at the Charles Square was to detect potential remains of the Holy Body Chapel and check the existence of a graveyard in its vicinity (Podliska [17]). The gothic building of the chapel worked for safekeeping and exhibiting of the crown jewels during the reigning of the emperor Charles IV (1346–1378 AD). There were assumptions that the chapel’s foundations may lay under a frequent road with a strong tram and car transportation. The road is mainly covered by asphalt; additionally, there are rails of the tram track in the road (Figure 2). The geophysical works were carried out due to proposed pedestrian subway within the revitalization project. The city

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2.1.1. Charles Square (Karlovo Námˇestí) The main goal of the works at the Charles Square was to detect potential remains of the Holy Body Chapel and check the existence of a graveyard in its vicinity (Podliska [17]). The gothic building of the chapel worked for safekeeping and exhibiting of the crown jewels during the reigning of the emperor Charles IV (1346–1378 AD). There were assumptions that the chapel’s foundations may lay under a frequent road with a strong tram and car transportation. The road is mainly covered by asphalt; additionally, there are rails of the tram track in the road (Figure2). The geophysical works were carried Geosciences 2020, 10, x FOR PEER REVIEW 3 of 26 out due to proposed pedestrian subway within the revitalization project. The city council conditioned councilthe building conditioned of a subway the building to prevent of from a subway any potential to prevent collisions from any with potential the chapel’s collisions foundations with the or chapellocal burial’s foundations area. or local burial area.

Figure 2. CenterCenter of of the the Cha Charlesrles Square with St. Ignac Ignac Church. Remains Remains of of the the Holy Holy Body Body Chapel were situated under tram rails and tram stop.

2.1.2. Old Town Square (Staromˇestsk(Staroměstskéé NNáměstíámˇestí)) The Old Town SquareSquare representsrepresents a a relatively relatively free free space space with with a a large large memorial memorial of of Jan Jan Hus Hus (one (one of ofthe the first first reformers reformers of of the the Church) Church) in in its its center center (Figure (Figure3). 3) Nearby,. Nearby the, the memorial memorial a a recently recently built-upbuilt-up replica of the Maria Pillar stands (was built on thethe originaloriginal building’sbuilding’s foundations). The The Old Town Square has a long history mainly connected to the era ofof gothicgothic architecturearchitecture (Figure(Figure4 4)).. TheThe olderolder cultculturalural layerslayers areare interfered interfered by by younger younger activities activities (Havrda (Havrda [18 ]).[18]). During During the 20ththe 20th century, century a tram, a tracktram wastrack passing was passing through through the center the of center the square of the but square was removed but was in removed the 50th. Thein the site 50th. was intersected The site was by intersectedthe excavation by worksthe excavation for a concurrent works for water a concurrent pipeline, sewage water andpipeline, cable sewage lines. The and tubes cable of lines. the metro The tlineubes and of the technical metro tunnelsline and lietechnical deeper tunnels under the lie deeper cultural under layers. the The cultural main layers. reason The for carryingmain reason out thefor carryinggeophysical out measurementsthe geophysical was measurements to identify the was current to identify state of the geological current bedrockstate of viageological non-destructive bedrock viamethods non-destructive with respect methods to potential with respect historical to potential objects. These historical findings objects. are These being findings used by are archaeologists being used byand archaeologists the city council’s and membersthe city council for planning’s members technical for planning activities technical at the square. activities at the square.

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Figure 3.Figure The Old 3. The Town Old Town Squa Square,Square, monumentre, monument of of Jan Jan Hus,Hus, Church Church of Motherof Mother of God of beforeGod before TTýnýn and Týn in and in foregroundforeground the Magneto thethe MagnetoMagneto MXPDA MXPDAMXPDA magnetometry magnetometrymagnetometry systemsystem (Sensys).(Sensys). (Sensys).

Figure 4. The map of the Old Town Square (“Altstädter Ring”) from 1842 (by CUZK, the State Administration of Land Surveying and Cadastre).

2.1.3. Hradčany Square (Hradčanske Náměstí) The Hradčany square lies in a close proximity of the Prague Castle (Figure 5) and, since the Figure 4.Figure The 4. mapThe map of of the the Old Town Town Square Square (“Altstädter (“Altstädter Ring”) from Ring”) 1842 (by CUZK, from the 1842 State (by Administration CUZK, the State 1980s, has been extensively archaeologically researched. The square has not been exposed to any Administrationof Land Surveying of Land and Surveying Cadastre). and Cadastre). remarkable building activity in the modern age. Apart from the rescue archaeological survey in the central part in 1944, no significant spatial outcrops were carried out, but only documentation of the 2.1.3. Hradčanyengineering Square networks (Hradčanske’ linear outcrops Náměstí (Blažková) [19], Mašterová [20]). From a geophysicist’s point Theof Hradčany view, we can square consider lies the insquare a close as a mainly proximity non-built of -theup area Prague with a Castle park in its(Figure middle. 5) The and most, since the important activity changing the original state-of-manner of the square is probably the fire water pool 1980s, has been extensively archaeologically researched. The square has not been exposed to any remarkable building activity in the modern age. Apart from the rescue archaeological survey in the central part in 1944, no significant spatial outcrops were carried out, but only documentation of the engineering networks’ linear outcrops (Blažková [19], Mašterová [20]). From a geophysicist’s point of view, we can consider the square as a mainly non-built-up area with a park in its middle. The most important activity changing the original state-of-manner of the square is probably the fire water pool

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2.1.3. HradˇcanySquare (HradˇcanskeNámˇestí) GeosciencesThe 20 Hradˇcanysquare20, 10, x FOR PEER liesREVIEW in a close proximity of the Prague Castle (Figure5) and, since the 1980s,5 of 26 has been extensively archaeologically researched. The square has not been exposed to any remarkable made in 1944, providing water in the end of World War II. During its construction, a Romanesque building activity in the modern age. Apart from the rescue archaeological survey in the central part living house was found and partly disrupted (Frolík [21]). After World War II, the pool was in 1944, no significant spatial outcrops were carried out, but only documentation of the engineering destroyed. networks’ linear outcrops (Blažková [19], Mašterová [20]). From a geophysicist’s point of view, we can The square is being visited by tourists during the day (Figure 5); hence, most of the works were consider the square as a mainly non-built-up area with a park in its middle. The most important carried out in night. The main goal of the geophysical measurements at the square was verification activity changing the original state-of-manner of the square is probably the fire water pool made in of the presence of several assumed archaeological objects, mainly stone buildings from the 12th and 1944, providing water in the end of World War II. During its construction, a Romanesque living house 13th centuries (and also medieval trenches). Gaining findings for newly planned construction was found and partly disrupted (Frolík [21]). After World War II, the pool was destroyed. activities was not crucial here, as there are no ongoing plans for the square’s revitalization.

Figure 5. The HradˇcanyHradčany Square. Square. In theIn the foreground foreground is our is geophysicist our geophysicist with the with CMD-MiniExplorer the CMD-MiniExplorer instrument. instrument. The square is being visited by tourists during the day (Figure5); hence, most of the works were 2.1.4.carried Lesser out in Town night. Square The main (Malostranské goal of the Náměstí geophysical) measurements at the square was verification of the presenceThe Lesser of severalTown Square assumed is archaeologicalcomposed of so objects,-called mainly Upper stone and Lower buildings square from (Figure the 12ths 6 and and 13th 7). Thecenturies Lower (and one also makes medieval the eastern trenches). and the Gaining Upper findings one the forwestern newly part. planned The lower construction square is activities intersected was bynot the crucial city tram here, lines. as there There are noare ongoingextensive plans transportation for the square’s and tourist revitalization. activities at the square. The last significant action within the square was the fire water tank built in the end of World War II, covering 2.1.4. Lesser Town Square (Malostranské Námˇestí) approximately half of the Lower square. The goal Lesser of Townthe measurements Square is composed was to bring of so-called an overall Upper geophysical and Lower picture square of (Figuresthe square6 and in 7the). limitsThe Lower of local one makes technical the eastern and transport and the Upper conditions. one the The western findings part. The are lower intended square for is the intersected needs by of archaeologicalthe city tram lines. research There arebut extensive also for preparing transportation the andrevitalization tourist activities of these at theareas. square. The last significant actionThe within area the of squarethe Lesser was Town the fire Square water tankbelongs built, from in the an end archaeological of World War II,point covering of view approximately, to the key areashalf of of the the Lower oldest square. settlement of the left-bank suburb of the Prague castle. The settlement of current Lesser Town is proved to be older than of the inhabitants of the opposite bank of the Vltava river, i.e., the current Old Town (Čiháková [22,23] a Cymbalak [24]).

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Figure 6. Lesser Town Square with a gravimeter. Figure 6. Lesser Town Square with a gravimeter.

Figure 7. Lesser Town Square (aerial photograph) with the eastern and western parts. Figure 7. Lesser Town Square (aerial photograph) with the eastern and western parts. Figure 7. Lesser Town Square (aerial photograph) with the eastern and western parts. 2.1.5. Armenian Sites 2.1.5. Armenian Sites The goal of the Armenia-based activities was to help in developing the Armavir province, The goal of the Armenia-based activities was to help in developing the Armavir province, namely in the field of tourism and ecology. Three joint geophysical and archaeological expeditions namely in the field of tourism and ecology. Three joint geophysical and archaeological expeditions were organized. The geophysical investigation was arranged as preliminary study which can open were organized. The geophysical investigation was arranged as preliminary study which can open

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The goal of the measurements was to bring an overall geophysical picture of the square in the limits of local technical and transport conditions. The findings are intended for the needs of archaeological research but also for preparing the revitalization of these areas. The area of the Lesser Town Square belongs, from an archaeological point of view, to the key areas of the oldest settlement of the left-bank suburb of the Prague castle. The settlement of current Lesser Town is proved to be older than of the inhabitants of the opposite bank of the Vltava river, Geosciences 2020, 10i.e.,, x the FOR current PEER Old REVIEW Town (Cihˇ áková [22,23] a Cymbalak [24]). 7 of 26

2.1.5. Armenian Sites bigger next projects in Armenia. During these expeditions, the survey works were carried out at pre- The goal of the Armenia-based activities was to help in developing the Armavir province, namely chosen archaeologicallyin the field of tourisminterested and ecology. sites (Simonyan Three joint geophysical [25] and and Avestisyan archaeological expeditions[26]). While were doing this, the first business negotiatorganized.ions The geophysical were conducted investigation (heads was arranged of the as preliminaryprovince, study Ministry which can of openthe biggerculture of Armenia next projects in Armenia. During these expeditions, the survey works were carried out at pre-chosen and Institute ofarchaeologically the archaeology interested and sites (Simonyanethnography [25] and Avestisyanof the National [26]). While academy doing this, the of first science business of the Republic of Armenia). negotiations were conducted (heads of the province, Ministry of the culture of Armenia and Institute The Armavirof the archaeologyprovince andlies ethnography in the western of the National rim of academy the country of science of(Fig theure Republic 8). Studied of Armenia). settlement sites The Armavir province lies in the western rim of the country (Figure8). Studied settlement sites were preliminarywere preliminarydated to datedthe Bronze to the Bronze Age Age or or Iron Iron Age. Age. The The sites weresites made were of themade volcanic of rocksthe volcanic rocks (Figure 9). (Figure9).

FigureFigure 8. Map 8. Map of ofArmenia, Armenia, Armavir Armavir province. province.

Figure 9. Armenia, Armavir province, Aygeshat site with traces of Iron Age cemetery.

2.2. Methodology Within the geophysical research works, a set of geophysical methods, adapted to given tasks and technical possibilities, was used.

Geosciences 2020, 10, x FOR PEER REVIEW 7 of 26 bigger next projects in Armenia. During these expeditions, the survey works were carried out at pre- chosen archaeologically interested sites (Simonyan [25] and Avestisyan [26]). While doing this, the first business negotiations were conducted (heads of the province, Ministry of the culture of Armenia and Institute of the archaeology and ethnography of the National academy of science of the Republic of Armenia). The Armavir province lies in the western rim of the country (Figure 8). Studied settlement sites were preliminary dated to the Bronze Age or Iron Age. The sites were made of the volcanic rocks (Figure 9).

Geosciences 2020, 10, 356 8 of 26 Figure 8. Map of Armenia, Armavir province.

FigureFigure 9. 9. Armenia,Armenia, Armavir Armavir province, province, Aygeshat Aygeshat site with traces of I Ironron Age cemetery.

2.2. Methodology Methodology Within thethe geophysicalgeophysical research research works, works a, seta set of of geophysical geophysical methods, methods, adapted adapted to given to given tasks tasks and Geosciencesandtechnical technical 20 possibilities,20, 10possibilities,, x FOR PEER was REVIEWwas used. used. 8 of 26

2.2.1. Magnetometry Magnetometry The magnetometric magnetometric measurements measurements were were carried carried out inout the in form the of form observing of obser theving vertical the gradient vertical of the magnetic field. All Armenian sites and a part of the Old Town Square were measured via the gradient of the magnetic field. All Armenian sites and a part of the Old Town Square were measured viaproton the proton PGM-1 PGM (manufacturer-1 (manufacturer SatisGeo, SatisGeo, Brno, Brno, Czech Czech Republic) Republic gradient) gradient meter meter (Figure (Figure 10). 10) For. For the theother other tasks, tasks the, Magnetothe Magneto MXPDA MXPDA by Sensys by Sensys was was used used (Figure (Figure2). In 2). the In most the most di ffi cultdifficult places places to pass to passthrough through the field, the thefield Magneto, the Magneto system system enables enables the single-channel the single-channel mode as mode well. as The well. Magneto The Magneto MXPDA MXPDAis also a gradientis also a metergradient system meter but system with fluxgate but with sensors. fluxgate The sensors. motion The of bothmotion instruments of both instruments in the field wasin the mapped field was via mapped GPS. In via some GPS. cases, In some we encountered cases, we encountered a loss of the a GPS losssignal of the andGPS the signal geophysical and the geophysicalprofiles had toprofiles be leveled had to via be classic leveled geodetic via classic techniques. geodetic techniques.

Figure 10. Armenia,Armenia, Armavir province. PGM PGM-1-1 gradient gradient meter. meter.

The MXPDA system allows very dense measurement, works mainly in the grid of 20 × 20 cm. The measurements network of the PGM-1 was mainly 1 × 1 m.

2.2.2. DEMP (Dipole Electromagnetic Profiling) The DEMP measurements were carried out via the CMD-MiniExplorer instrument by GF Instruments, measuring in one transmitting frequency on the three pairs of measuring coils (with their central spacings of 0.32, 0.71 and 1.18 m). The results are in the form of frequency-dependent resistivity in ohmmeters in approximate depths that are based on the manufacturer’s (GF Instruments testing base) calibrations and equal to 0.5, 1 and 1.8 m. Gained data were (after downloading) mainly displayed in the form of the 2D apparent resistivity and magnetic gradient maps. In several cases, the DEMP data had to be filtered, as the high resistivities of the volcanic rocks caused erroneous values due to collapse of the factory calibration and recalculation into the apparent resistivities. The DEMP method was being routinely used at the Armenian sites (Figure 11). In Prague, this method was used at the Old Town Square and Hradčany Square.

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The MXPDA system allows very dense measurement, works mainly in the grid of 20 20 cm. × The measurements network of the PGM-1 was mainly 1 1 m. × 2.2.2. DEMP (Dipole Electromagnetic Profiling) The DEMP measurements were carried out via the CMD-MiniExplorer instrument by GF Instruments, measuring in one transmitting frequency on the three pairs of measuring coils (with their central spacings of 0.32, 0.71 and 1.18 m). The results are in the form of frequency-dependent resistivity in ohmmeters in approximate depths that are based on the manufacturer’s (GF Instruments testing base) calibrations and equal to 0.5, 1 and 1.8 m. Gained data were (after downloading) mainly displayed in the form of the 2D apparent resistivity and magnetic gradient maps. In several cases, the DEMP data had to be filtered, as the high resistivities of the volcanic rocks caused erroneous values due to collapse of the factory calibration and recalculation into the apparent resistivities. The DEMP method was being routinely used at the Armenian sites (Figure 11). In Prague, this method was used at the Old Town Square and HradˇcanySquare. Geosciences 2020, 10, x FOR PEER REVIEW 9 of 26

Figure 11. Armenia,Armenia, Armavir Armavir province. province. CMD CMD-MiniExplorer.-MiniExplorer.

2.2.3. GPR GPR (Ground (Ground Penetrating Radar) The radar measurementsmeasurements were were carried carried out out via via the the SIR-20 SIR- (GSSI)20 (GSSI) instrument instrument with with 100- 100 and- 400-MHzand 400- MHzantennas. antennas. The profile The profile spacing spacing was mainlywas mainly 2.5 m. 2.5 The m. in-lineThe in-line scanning scanning frequency frequency was was mainly mainly 10 cm. 10 cm.The qualityThe quality of the of records the records was controlled was controlled by an operator by an operator while measuring while measuring on the PC on screen the (Figure PC screen 12). (DetailedFigure 12) data. Detailed processing, data their processin filtration,g, their gaining, filtration, etc., wasgaining carried, etc. out, was afterwards carried in-oout ffiafterwardsce. in- office.

Figure 12. Old Town Square. Geological radar SIR 20 with 400- and 100-MHz antenna systems.

2.2.4. ERT (Resistivity Tomography) For the ERT measurements the ARES II. instrument was used (GF Instruments, Brno, Czech Republic). Multielectrode measurements were mostly carried out using 48 electrodes; their spacing was mainly 2 m. While measuring in the Prague downtown, we encountered issues with electrodes fixation in the cobblestones. This issue was solved by using thin electrodes placed into slits (Figure 13).

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Figure 11. Armenia, Armavir province. CMD-MiniExplorer.

2.2.3. GPR (Ground Penetrating Radar) The radar measurements were carried out via the SIR-20 (GSSI) instrument with 100- and 400- MHz antennas. The profile spacing was mainly 2.5 m. The in-line scanning frequency was mainly 10 cm. The quality of the records was controlled by an operator while measuring on the PC screen Geosciences(Figure 12)2020. ,Detailed10, 356 data processing, their filtration, gaining, etc., was carried out afterwards10 of in 26- office.

FigureFigure 12.12. Old Town Square.Square. Geological radar SIR 2020 withwith 400-400- andand 100-MHz100-MHz antennaantenna systems.systems.

2.2.4.2.2.4. ERT (Resistivity Tomography)Tomography) ForFor thethe ERT ERT measurements measurements the the ARES ARES II. instrument II. instrument was used was (GF used Instruments, (GF Instruments Brno, Czech, Brno, Republic). Czech MultielectrodeRepublic). Multielectrode measurements measurements were mostly were carried mostly out usingcarried 48 out electrodes; using 48 their electrodes spacing; their was spacing mainly 2was m. mainly While measuring2 m. While in measuring the Prague in downtown, the Prague we downtown encountered, we issuesencountered with electrodes issues with fixation electrodes in the cobblestones.fixation in the This cobblestones. issue was solved This issue by using was thin solved electrodes by using placed thin into electrodes slits (Figure placed 13). into slits (Figure Geosciences 2020, 10, x FOR PEER REVIEW 10 of 26 13).

Figure 13. HradčanyHradˇcanySquare. Square. Geoelectrical Geoelectrical system system ARES ARES II II and and electrodes electrodes on the profile. profile.

2.2.5. Gravimetry Gravimetry Surveying Surveying For the microgravimetric measurementsmeasurements,, CG CG-5-5 and CGCG-6-6 (Scint(Scintrex)rex) instruments were used ((FigureFigure6 6)).. TheThe prevailingprevailing spacingspacing ofof thethe stationsstations waswas 22 m.m. TheThe altitudealtitude ofof thethe gravimetricgravimetric stationsstations waswas measured by the total levelling station Leice Sprinter 150 M. The position of the gravimetric gravimetric and other geophysical profiles profiles was set by the GNSS receiver TrimbleTrimble R8sR8s (Figure(Figure 14 14))..

Figure 14. Trimble R8s at the Lesser Town Square in the times of coronavirus.

2.2.6. Seismics For the seismic measurements, the Terraloc Mk-6 (Figure 15) and Terraloc Pro 2 48 channels instruments were used. The seismic shots were generated by the blows of a seismic hammer onto a plastic plate. The geophones spacing was mainly 2 m. The seismic methods were used only at the Prague sites. Measured data were gained so they could have been transformed into the forms of seismic refraction, reflection and tomography. At the Old Town Square, a less used time-term method was used.

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Figure 13. Hradčany Square. Geoelectrical system ARES II and electrodes on the profile.

2.2.5. Gravimetry Surveying For the microgravimetric measurements, CG-5 and CG-6 (Scintrex) instruments were used (Figure 6). The prevailing spacing of the stations was 2 m. The altitude of the gravimetric stations was Geosciencesmeasured2020 by, the10, 356 total levelling station Leice Sprinter 150 M. The position of the gravimetric and11 other of 26 geophysical profiles was set by the GNSS receiver Trimble R8s (Figure 14).

FigureFigure 14. TrimbleTrimble R8s at the Lesser Town Square in the times of coronavirus.

2.2.6.2.2.6. Seismics For the seismic measurements, the Terraloc Mk Mk-6-6 ( (FigureFigure 15)15) and Terraloc Pro 2 48 channels instruments were used. The The seismic seismic shots shots we werere generated by the blows of a seismic hammer onto a plastic plate. The The geophones spacing was mainly 2 m.m. The The seismic seismic methods methods were used only at the Prague sites.sites. MeasuredMeasured data data were were gained gained so theyso they could could have have been been transformed transformed into the into forms the offorms seismic of seismicrefraction, refraction, reflection reflection and tomography. and tomography. At the Old At Town the Old Square, Town a Square, less used a less time-term used time method-term was method used. Geosciences 2020, 10, x FOR PEER REVIEW 11 of 26 was used.

FigureFigure 15. SeismicSeismic instrument instrument Terraloc Terraloc Mk Mk-6-6 at the Old Town Square.

2.2.7. Data Processing For the data processing, the following software was used:  Reflex W (seismic data processing);  Rayfract 386 (seismic data processing);  Radan (GPR);  Res2DInv (resistivity tomography);  Fast Grav (gravity data processing);  Mag (gravity data processing);  Geosoft (databases);  Excel (databases);  Voxler 4 (4D processing);  Surfer 17 (3D pictures);  Grapher 16 (2D and 3D graphs). The abovementioned software can be found under their names on websites with a more detailed description of their features. An exception is the Mag program (gravity measurements), which is installed only on G IMPULS Prague computers. During the data processing and the subsequent evaluation, a set of programs was used which has proven its qualities to our team for a long time. The Reflex W program enables the export of seismic data from the seismic instrument to a computer, when the format is changed to the Seg2 format, which is standardly used in seismic processing programs. After frequency analysis, filtration and adjustment of the gain of individual seismic traces, one can chose processing by the method of seismic reflection or refraction. Seismic data were measured in the field so that both basic processing methods could be used, i.e., reflection and refraction. The space between the individual seismic profiles was examined by the method of seismic tomography, i.e., seismic sensors were placed on one profile and seismic sources were excited on the adjacent profile. The program for seismic tomography is a part of the Reflex W software package, but for comparison you can also use the Rayfract 386 program, which works with slightly different velocity models. Experience shows that the Rayfract 386 program works very well for environments with a continuously increasing velocity gradient to depth. For tasks related to depths up to the first meters (which is typical for archeology), mainly waves with higher frequencies (up to hundreds of Hz) were used and mainly transverse waves were monitored. The Reflex W program was also used to process radar records, because radar waves have essentially similar behavior to seismic waves; the change is only in the frequency and velocity of

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2.2.7. Data Processing For the data processing, the following software was used:

Reflex W (seismic data processing); • Rayfract 386 (seismic data processing); • Radan (GPR); • Res2DInv (resistivity tomography); • Fast Grav (gravity data processing); • Mag (gravity data processing); • Geosoft (databases); • Excel (databases); • Voxler 4 (4D processing); • Surfer 17 (3D pictures); • Grapher 16 (2D and 3D graphs). • The abovementioned software can be found under their names on websites with a more detailed description of their features. An exception is the Mag program (gravity measurements), which is installed only on G IMPULS Prague computers. During the data processing and the subsequent evaluation, a set of programs was used which has proven its qualities to our team for a long time. The Reflex W program enables the export of seismic data from the seismic instrument to a computer, when the format is changed to the Seg2 format, which is standardly used in seismic processing programs. After frequency analysis, filtration and adjustment of the gain of individual seismic traces, one can chose processing by the method of seismic reflection or refraction. Seismic data were measured in the field so that both basic processing methods could be used, i.e., reflection and refraction. The space between the individual seismic profiles was examined by the method of seismic tomography, i.e., seismic sensors were placed on one profile and seismic sources were excited on the adjacent profile. The program for seismic tomography is a part of the Reflex W software package, but for comparison you can also use the Rayfract 386 program, which works with slightly different velocity models. Experience shows that the Rayfract 386 program works very well for environments with a continuously increasing velocity gradient to depth. For tasks related to depths up to the first meters (which is typical for archeology), mainly waves with higher frequencies (up to hundreds of Hz) were used and mainly transverse waves were monitored. The Reflex W program was also used to process radar records, because radar waves have essentially similar behavior to seismic waves; the change is only in the frequency and velocity of wave propagation. Simultaneously with the interpretation using the Reflex program, the radar records were also processed using the Radan 6 radar program. The implementation outputs from both programs were roughly identical. The program Res2Dinv was used for resistivity measurements. It is a set of processing and interpretation programs focused mainly on multielectrode measurements, which are evaluated in the form of resistivity tomography (ERT). The final output is resistivity cross-sections compiled from the values of the interpreted actual resistivities. In practice, however, it is necessary to realize that the interpretation of real resistivities is always, to some extent, influenced by our initial concept of the structure of the studied environment. Hence, the resistivity cross-sections are models whose reliability is affected by the operator’s experience and basic knowledge of the composition of the investigated environment and its physical properties. In some cases, it is possible to prefer sections composed of directly measured data (apparent resistivities) that are not affected by a subjective approach to interpretation. Geosciences 2020, 10, 356 13 of 26

For dipole electromagnetic profiling, a program supplied by the instrument manufacturer (GF Instruments, Brno, Czech Republic) was used for processing. GF Instruments’ devices are calibrated at the company’s test base, and thus the depth ranges of penetration of electromagnetic waves into the rock environment and their behavior in a layered or otherwise arranged environment are also tested by field practice. This is important because the reliability of laboratory model tests or theoretical calculations have their limits in electromagnetic fields. For gravity measurements, the Mag evaluation program was preferably used, as it enables the creation of both layered gravity models and monitoring of the influence of spatially limited formations (sphere, cone, etc.). This program was created in the DOS environment and is, therefore, being gradually replaced by the Fast Grav program, which is fully compatible with the Windows 10 environment. Programs of the Golden Software series (Grapher, Surfer, Voxler) were used for graphic processing. The Oasis Montaje program (Geosoft) was used to manage large volumes of data.

2.3. Project Management Sites in Prague were measured via a wide spectrum of methods. Geophysical campaign was carried out by a team of approximately seven persons which allowed simultaneous measuring using several methods. The work shift was mainly in the nighttime with less traffic going on on-site. In several cases, the measurements were assisted by the municipal police stopping the traffic completely. After each shift, the measured data were downloaded off the instruments and primarily checked. After the data were uploaded into the office server, the data processing and evaluation could have started. Entire raw data and other outputs are archived and are permanently available for the needs of authorized users. Each particular project (site) has its own concluding report. The report represents current assignments of the contractor and its actual needs. However, the way of archiving the measured data and their processing allows consequent use of the results reinterpretation in the later stages so the results can be updated upon new requests of the database’s users. Different approach was chosen for the Armenia expeditions. Limited budgets of the international expeditions, declare limitations, etc., would not allow the use of wider complex of geophysical methods in the initial projects. The used methods were mainly magnetometry and DEMP. With respect to favorable geological and physical properties (volcanic rocks on the sites), even the limited methodology brought necessary findings for further development of the works. For each field day, a schedule of geophysical works was planned according to the time constraints and field conditions. Every evening after finishing the field works, the data were downloaded and primarily processed. After discussion on the preliminary results, the work plan for the next days was made. Final data processing and reporting were finished after coming back to the Czech Republic.

3. Results

3.1. Charles Square In the central part of the Charles Square, the spatial GPR survey, seismic refraction measurement, ERT and gravimetry were carried out. The complex of methods allowed to roughly map out zones with remains of the chapel and graveyard which were partly proved by the sounding works (Figure 16). From a methodological point of view, we found that the ERT method is able to detect Middle Age burial areas as the graves with the mortal remains manifest as smaller objects of low resistivity (Figure 17). After excavation of the tomb, this fact was explained as the influence of decomposed soft tissues of a body (organic material has low resistivity). Geosciences 2020, 10, x FOR PEER REVIEW 13 of 26

Geosciences 2020, 10, x FOR PEER REVIEW 13 of 26 3. Results

3. Results3.1. Charles Square

3.1. Charles InSquare the central part of the Charles Square, the spatial GPR survey, seismic refraction Geosciencesmeasurement,2020, 10, 356 ERT and gravimetry were carried out. The complex of methods allowed to 14roughly of 26 map out zones with remains of the chapel and graveyard which were partly proved by the sounding works (Figure 16). In theThe results central of partmeasurements of the Charlesat the Charles Square Square, the could spatial be verified GPR by survey, a limited seismic archaeological refraction measurement,survey (Podliska ERT [and17]). gravimetry The location were of the masonrycarried out. of the The defunct complex chapel of was methods confirmed, allowed as well to as roughly the map identificationout zones with of graves remains detected of the geophysically chapel and graveyard (Figure 18). which The preparation were partly of a proved pedestrian by underpass the sounding in this place was stopped. works (Figure 16).

Figure 16. Charles Square. The archival map with the foundation of the chapel (Helgert, 19th Century) with principal geophysical anomalies indicating single graves or tombs. Archaeological test pits are marked in red.

From a methodological point of view, we found that the ERT method is able to detect Middle Age burial areas as the graves with the mortal remains manifest as smaller objects of low resistivity (Figure 17). After excavation of the tomb, this fact was explained as the influence of decomposed soft FigureFigure 16. Charles 16. Charles Square. Square. The The archival archival map map with with the the foundation of of the the chapel chapel (Helgert, (Helgert, 19th 19th Century) Century) tissues of a body (organic material has low resistivity). withwith principal principal geophysical geophysical anomalies anomalies indicating indicating single gravesgraves or or tombs. tombs. Archaeological Archaeological test test pits pits are are marked in red. marked in red.

From a methodological point of view, we found that the ERT method is able to detect Middle Age burial areas as the graves with the mortal remains manifest as smaller objects of low resistivity (Figure 17). After excavation of the tomb, this fact was explained as the influence of decomposed soft tissues of a body (organic material has low resistivity).

Figure 17. Charles Square. The resistivity cross-section (ERT) with indications of the graves (see small crosses). Figure 17. Charles Square. The resistivity cross-section (ERT) with indications of the graves (see small crosses).

The results of measurements at the Charles Square could be verified by a limited archaeological survey (Podliska [17]). The location of the masonry of the defunct chapel was confirmed, as well as

Figure 17. Charles Square. The resistivity cross-section (ERT) with indications of the graves (see small crosses).

Geosciences 2020, 10, x FOR PEER REVIEW 14 of 26 theGeosciences identification2020, 10, 356 of graves detected geophysically (Figure 18). The preparation of a pedestrian15 of 26 underpass in this place was stopped.

Figure 18. Charles Square. Grave with skeleton which was detected by ERT. Figure 18. Charles Square. Grave with skeleton which was detected by ERT.

3.2. Old Old Town Town Square Within the the Old Old Town Town Square Square area, area, a detailed a detailed survey survey was was carried carried out, covering out, covering not only not the only square the squareitself but itself aimed but aimed also to also the areato the of area expected of expected remains remains of burned of burned down down gothic gothic revival revival town town hall wing hall wing(a consequence (a consequence of World of World War II).War From II). From a methodological a methodological point point of view, of view, we wouldwe would like like to stressto stress an anexperiment experiment with with measured measured magnetometric magnetometric data. data. Our experimentOur experiment was partly was inspired partly inspired by a common by a commonway of micro way gravimetryof micro gravimetry data processing data processing when the when regional the fieldregional is subtracted field is subtracted from the from Bouguer the Bougueranomalies. anomalies. For the interpretation,For the interpretation we then, we get then the residualget the residual anomalies, anomalies, locally locally limited, limited, which canwhich be canconsidered be considered as caused as bycaused local by objects local closeobjects to theclose surface. to the Figuresurface. 19 Figure shows 19 the shows unprocessed the unprocessed measured measureddata of the data vertical of the magnetic vertical gradient magnetic in gradient 3D and 2D. in 3D Figure and 20 2D. shows Figure the 20 map shows of magnetic the map valuesof magnetic made valuesby extraction made by of extracti the valueson of between the values+ and between100 gama. + and The−100 map gama. expresses The map low expres valuesses of low the values gradient of − theby greengradient color, by thegreen other color, areas the remain other areas white. remain This way white. of displayingThis way of allows displaying some allows sort of structuressome sort of or structuresdirections (blueor directions lines) to (blue be followed, lines) to which be followed, cannot bewhich explained cannot as be known explained objects as (sewage, known objects cables, (sewage,light poles, cables, etc.).The light determinedpoles, etc.).The values determined will be thevalues subject will ofbe archaeologicalthe subject of archaeological research in the research future, inwhich the future, is organizationally which is organizationally and technically and demanding technically due demanding to the intensive due to tratheffi intensivec in this publictraffic in area. this publicMeasured area. magnetic field is going to be further investigated via techniques of spatial analysis, whichMeasured is traditionally magnetic being field used is going for the to aerial be further geophysical investigated data processing. via techniques of spatial analysis, which is traditionally being used for the aerial geophysical data processing.

Geosciences 2020, 10, 356 16 of 26 Geosciences 2020, 10, x FOR PEER REVIEW 15 of 26

FigureFigure 19. 19.Old Old Town Town Square. Square. 2D 2D (above) (above) and and 3D 3D (bottom) (bottom) images images of of the the vertical vertical gradient gradient magnetic magnetic fieldfield in in the the unprocessed unprocessed measured measured data. data.

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Figure 20. Old Town Square. The map of areas with low intensity values ( 100 gamma). Low values ± ofFigure the gradient 20. Old are Town marked Square. by The green map color, of areas the otherwith low areas intensity remain values white. (± 1—Structure 100 gamma). isLow probably values an indicationof the gradient of so-far are undiscoveredmarked by green marketplace; color, the other 2, 3 andareas 4 areremain probably white. traces1—Structure of the activitiesis probably around an theindication defunct fountainof so-far undiscovered (4) and Maria marketplace memorial (2,; 2, 3). 3 and 4 are probably traces of the activities around the defunct fountain (4) and Maria memorial (2, 3). 3.3. HradˇcanySquare 3.3. Hradčany Square The non-destructive geophysical survey aimed to cover a whole area (if possible) of the square and accordingThe non- todestructive the complex geophysical geophysical survey methodology aimed to cover to a describe whole area in detail (if possible) the bedrock’s of the square state of mannerand according and totry to the to define complex and geophysical localize any methodology archaeological to des structures’cribe in detail indications. the bedrock The’s Hradˇcanystate of squaremanner has and not to been try exposedto define toand any localize construction any archaeological or research activitiesstructures in’ indications. present days. The Excluding Hradčany the rescuingsquare archaeologicalhas not been exposed 1944 survey to any inconstruction the central or part research no significant activities spatial in present outcrops days. haveExcluding been the made, onlyrescuing the linear archaeol trenches’ogical documentation 1944 survey in of the the central engineering part no networks. significant The spatial chosen outcrops methodology have been aimed mainlymade, to only identify the linear assumed trenches north–south’ documentation medieval of the trenches engineering going networks. across the The square. chosen methodology aimedWe usedmainly a setto identify of geophysical assumed methods north–south as follows: medieval trenches going across the square. We used a set of geophysical methods as follows: Spatial magnetometry; •  Spatial magnetometry; Spatial geological radar (GPR); •  Spatial geological radar (GPR);  SpatialSpatial dipole dipole electromagnetic electromagnetic profilingprofiling (DEMP);(DEMP); •  ProfileProfile gravimetry; gravimetry; •  ProfileProfile complex complex seismics; seismics; •  ProfileProfile resistivity resistivity tomography tomography(ERT). (ERT). • The medieval trenches were detected by several geophysical methods (DEMP, gravimetry, not The medieval trenches were detected by several geophysical methods (DEMP, gravimetry, not so so much strongly seismic measurements and ERT). In Figure 20, the map of the area of interest with much strongly seismic measurements and ERT). In Figure 20, the map of the area of interest with isolines of conductivity is shown (result of the dipole electromagnetic profiling) with interpretation isolines of conductivity is shown (result of the dipole electromagnetic profiling) with interpretation of the medieval trenches. Figure 21 shows profiles where gravity measurement was carried out. In ofFigure the medieval 22, the gra trenches.phs of Bouguer Figure (gravity)21 shows anomalies profiles are where presented gravity together measurement with the wasinterpretation carried out. Inof Figure medieval 22, the trenches graphs (ditch of Bougueres). (gravity) anomalies are presented together with the interpretation of medieval trenches (ditches).

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FigureFigureFigure 21.21. HradčanyHradčanyHradˇcanySquare. Square.Square. The The The mapmap map withwith with isolinesisolines isolines ofof of conductivity conductivity conductivity (by(by (by DEMP),DEMP), DEMP), gravitygravity gravity profilesprofiles profiles andand and interpretationinterpretationinterpretation of of of the the the medieval medieval medieval trenches. trenches.

Figure 22. Hradčany Square. Graphs of residual Bouguer anomalies. Profiles in direction W-E.

FrequentFigure 22. objects Hradčany of varying Square. ages Graphs were of residualdetected Bouguer at the Hradčany anomalies. Square.Profiles inWhat direction surprised W-E. us was Figure 22. HradˇcanySquare. Graphs of residual Bouguer anomalies. Profiles in direction W-E. the detection of the underground water reservoir which lies in place of the old removed fire reservoir of WorldFrequent War objects II. This of new varying reservoir ages hadwere to detected be built at-up the secre Hradčanytly during Square. the Cold What War, surprised as there us iswas no theexisting detection documentation of the underground about the water object. reservoir The reservoir which liesis clearly in place visible of the on old the removed GPR results fire reservoir and as a ofsmall World negative War II. gravity This new anomaly reservoir (Figure had 23) to .be built-up secretly during the Cold War, as there is no existing documentation about the object. The reservoir is clearly visible on the GPR results and as a small negative gravity anomaly (Figure 23).

Geosciences 2020, 10, 356 19 of 26

Frequent objects of varying ages were detected at the HradˇcanySquare. What surprised us was the detection of the underground water reservoir which lies in place of the old removed fire reservoir of World War II. This new reservoir had to be built-up secretly during the Cold War, as there is no existing documentation about the object. The reservoir is clearly visible on the GPR results and as a small negative gravity anomaly (Figure 23). Geosciences 2020, 10, x FOR PEER REVIEW 18 of 26

Figure 23. Hradčany Square. GPR anomalies above the underground reservoir. Figure 23. HradˇcanySquare. GPR anomalies above the underground reservoir.

The data processing and preliminary interpretation of the magnetic measurement is shown in Figure 2424.. We start with original vertical gradients of the fieldfield data. The primal data are transformed into a regional regional field field,, i.e. i.e.,, the data data are are smoothed smoothed out out by by a a coarser coarser grid grid (see (see for for example example software software Surfer). Surfer). The final final analysis uses residual anomalies, i.e. i.e.,, a a difference difference between between measured measured data data and and regional regional data. data.

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FigureFigure 24. HraˇcanySquare. 24. Hračany Square. The analysis The analysis of the magnetic of the measurements magnetic measurements and preliminary and interpretation. preliminary interpretation.

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3.4. Lesser Town Square 3.4. Lesser Town Square At the Lesser Town Square, the contracting authority emphasized that the task of the At the Lesser Town Square, the contracting authority emphasized that the task of the measurement measurement is not only to discover clues that will be of interest to archaeologists, but that it is is not only to discover clues that will be of interest to archaeologists, but that it is important to important to obtain a summary of information that will also be used to plan the upcoming obtain a summary of information that will also be used to plan the upcoming revitalization of the revitalization of the square. When revitalizing the square, it is necessary to avoid objects that could square. When revitalizing the square, it is necessary to avoid objects that could be damaged by heavy be damaged by heavy mechanization and excavation work. For this reason, a comprehensive map of mechanization and excavation work. For this reason, a comprehensive map of significant geophysical significant geophysical anomalies was compiled (Figure 25). These places should not be disturbed by anomalies was compiled (Figure 25). These places should not be disturbed by deeper excavation deeper excavation work. Furthermore, the map contains hatched places where we expect a work. Furthermore, the map contains hatched places where we expect a consolidated environment consolidated environment in the first meters in depth. In these places, it is possible to store building in the first meters in depth. In these places, it is possible to store building material or park with material or park with construction mechanisms. construction mechanisms.

FigureFigure 25. Lesser 25. Lesser Town TownSquare. Square. Summary Summary of geophysical of geophysical results and results anomalies. and anomalies. G—gravity, G—gravity, M— magnetometry,M—magnetometry, E—resistivity, E—resistivity, I—underground I—underground utility. utility.

FigureFigure 26 shows 26 shows the radargrams, the radargrams, seismograms seismograms and andresistivity resistivity cross cross-section-section on the on profile the profile P155. P155. The The profile profile ran ran in in the the S S–N–N direction direction and and lies lies in in the the eastern eastern part part of the of square the square (the profiles (the profiles are numbered are numberedaccording according to the local to the network, local network, see Figure see Figure25). A red25). ellipsisA red ellipsis in Figure in Figure26 shows 26 shows correlated correlated anomalies anomaliesmanifested manifested via all via methods. all methods. This probablyThis probably equals equals to a disruptedto a disrupted area area after after the the excavation excavation works. works.Similarly, Similarly, one one can can observe observe other other anomalies, anomalies, too. too.

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Figure 26. Lesser Town Square. Summary of geophysical methods—ERT, seismic reflection and radar Figure 26. Lesser Town Square. Summary of geophysical methods—ERT, seismic reflection and radar onon thethe profileprofile P155.P155.

3.5.3.5. ArmeniaArmenia SitesSites DuringDuring three three expeditions, expeditions, about about 10 10 sites sites were were visited visited and and measured. measured. Almost Almost all all sites sites were were characterizedcharacterized by by the the fact fact that that the the foundations foundations of of buildings buildings and and other other archaeologically archaeologically interesting interesting objectsobjects werewere builtbuilt ofof volcanicvolcanic rockrock withwith increased magneticmagnetic susceptibility.susceptibility. OnOn thethe contrary, thethe fillingsfillings ofof gravesgraves or mounds were made of of very very fine fine-grained-grained soils soils with with high high conductivity. conductivity. For For this this reason, reason, it itwas was possible possible to to successfully successfully use use the the magnetometric magnetometric method method and and the DEMP (Dipole ElectromagneticElectromagnetic profiling)profiling) methodmethod for the reconnaissance reconnaissance phase phase of of the the work. work. For For the the detailed detailed stages stages of the of thesurvey, survey, we weplan plan a wider a wider complex complex of of geophysical geophysical measurements, measurements, which, which, however, however, requires more demanding demanding organizationalorganizational preparationpreparation andand financialfinancialsecurity. security.

3.5.1.3.5.1. GhanjyanGhanjyan BlurBlur SiteSite GhanjyanGhanjyan BlurBlur sitesite consistsconsists ofof thethe stonestone objectsobjects relicsrelics (shapes(shapes ofof medievalmedieval houseshouses oror prehistoricprehistoric graves)graves) coveredcovered byby remarkablyremarkably thickthick overlyingoverlying sediments.sediments. TheThe goalgoal ofof thethe measurementsmeasurements herehere waswas toto mapmap outout archaeologicalarchaeological featuresfeatures andand possiblypossibly guessguess onon thethe thicknessthickness ofof thethe sediments.sediments. TogetherTogether withwith geophysicalgeophysical measurements, measurements a, detaileda detailed sketch sketch and and sherd sherd analysis analysis of the of site the was site carried was carried out. We out. proved We existingproved largerexisting archaeological larger archaeological objects and objects detected and right-angleddetected right structures-angled structures (probably (probably walls—Figure walls 27—). Figure 27).

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Figure 27. Ghanjyan Blur. Example of the detailed measurement with indication of two 2D structures

(possibly walls). Figure 27.FigureGhanjyan 27. Ghanjyan Blur. Example Blur. Example of the detailed of the detailed measurement measurement with indication with indication of two 2D of structurestwo 2D structures 3.5.2.(possibly Lernamerdz(possibly walls). Site walls). 3.5.2. Lernamerdz Site Thus3.5.2. far, Lernamerdz the site is Site not researched sufficiently. However, the outcrops clearly show primitive figuresThus from far, the prehistoric site is not researched era (Figure su 28)ffi. ciently.Figure 29 However, shows the the geophysical outcrops clearly field measureme show primitivents on- Thus far, the site is not researched sufficiently. However, the outcrops clearly show primitive figuressite. from the prehistoric era (Figure 28). Figure 29 shows the geophysical field measurements on-site. figures from the prehistoric era (Figure 28). Figure 29 shows the geophysical field measurements on- site.

Geosciences 2020, 10, x FOR PEERFigure REVIEW 28. Lernamerdz. Manifestation of prehistorical activities. 23 of 26 Figure 28. Lernamerdz. Manifestation of prehistorical activities.

Figure 28. Lernamerdz. Manifestation of prehistorical activities.

Figure 29. Depiction of magnetic gradients registered at the Lernamerdz archaeological site. Figure 29. Depiction of magnetic gradients registered at the Lernamerdz archaeological site. 4. Discussion

Most geophysical works for archaeology, as we can see in the literature, focus on one small place of interest in order to specify the presence of objects whose physical properties can be assumed. The use of magnetometry prevails; the results were slightly less accurate using the GPR (geological radar). Successful measurements usually come from places where the work is not disturbed by the presence of engineering networks, stray currents, modern buildings, etc. From the literature and the authors’ own practice, it can be pointed out that geophysics is a valid help for archaeologists should the user of results asks right questions and presents a valid concept of the site of interest. For example, in Hrubec [27], an example of finding medieval marl walls is described. The geophysicist logically assumed that such objects were in the place of interest and mistakenly considered marl blocks of natural bedrock to be such objects. Geophysics monitors the physical properties of the environment and usually cannot comment on the historical age of the detected object. Budinský [28] provides an example that draws attention to changes in the physical properties of some rocks due to climate. Claystones, which seemed to be very solid and were characterized by high seismic velocities, became slurry due to wetting, and the originally measured high-velocity anomalies were no longer measurable. The examples presented here bring findings from research where geophysics is used less or is accepted with distrust. Measurements in paved squares and in places used for car and tram transport are very difficult for geophysical work. On the other hand, knowledge from such places provides information that can be used by archaeologists, historians, as well as experts preparing sensitive revitalizations of historic sites. The assignment of works, which we solved for the Prague urban area, represented the first phase of the work. By consistent and comprehensive measurement of the entire areas of interest, databases of direct geophysical data were obtained, which underwent initial data processing and the first interpretation. Our findings have mostly led to the fact that the density of information (geophysical anomalies) in areas of interest is considerable and their accurate qualitative interpretation is often possible only after a detailed discussion with other specialists. Thus, it is a teamwork-based activity in which archaeologists, historians, civil engineers can, in cooperation with geophysicists, use the measured geophysical database in future years (including reinterpretation of data, detailed geophysical surveys, etc.). Our work has shown that geophysical measurements in urban areas are possible with the right methodology. The experience of working in Armenia is contrasted in the present article. It is a measurement in natural, sparsely built-up terrain and, at the same time, under conditions of work with limited financial and material equipment. Work in Armenia provided the first experience that can be used for larger expeditions. On the basis of the good results using magnetometry and electromagnetic methods it is necessary to appeal for further research of this type as Armenia is very rich in historical monuments. In addition, it was the first measurement in Armenia at archaeological sites interpreted for prehistory and the Middle Ages as village settlements. Thus far, countless measurements have focused on prehistoric fortified sites. However, in addition to tourist attractions, these sites are

Geosciences 2020, 10, 356 24 of 26

4. Discussion Most geophysical works for archaeology, as we can see in the literature, focus on one small place of interest in order to specify the presence of objects whose physical properties can be assumed. The use of magnetometry prevails; the results were slightly less accurate using the GPR (geological radar). Successful measurements usually come from places where the work is not disturbed by the presence of engineering networks, stray currents, modern buildings, etc. From the literature and the authors’ own practice, it can be pointed out that geophysics is a valid help for archaeologists should the user of results asks right questions and presents a valid concept of the site of interest. For example, in Hrubec [27], an example of finding medieval marl walls is described. The geophysicist logically assumed that such objects were in the place of interest and mistakenly considered marl blocks of natural bedrock to be such objects. Geophysics monitors the physical properties of the environment and usually cannot comment on the historical age of the detected object. Budinský [28] provides an example that draws attention to changes in the physical properties of some rocks due to climate. Claystones, which seemed to be very solid and were characterized by high seismic velocities, became slurry due to wetting, and the originally measured high-velocity anomalies were no longer measurable. The examples presented here bring findings from research where geophysics is used less or is accepted with distrust. Measurements in paved squares and in places used for car and tram transport are very difficult for geophysical work. On the other hand, knowledge from such places provides information that can be used by archaeologists, historians, as well as experts preparing sensitive revitalizations of historic sites. The assignment of works, which we solved for the Prague urban area, represented the first phase of the work. By consistent and comprehensive measurement of the entire areas of interest, databases of direct geophysical data were obtained, which underwent initial data processing and the first interpretation. Our findings have mostly led to the fact that the density of information (geophysical anomalies) in areas of interest is considerable and their accurate qualitative interpretation is often possible only after a detailed discussion with other specialists. Thus, it is a teamwork-based activity in which archaeologists, historians, civil engineers can, in cooperation with geophysicists, use the measured geophysical database in future years (including reinterpretation of data, detailed geophysical surveys, etc.). Our work has shown that geophysical measurements in urban areas are possible with the right methodology. The experience of working in Armenia is contrasted in the present article. It is a measurement in natural, sparsely built-up terrain and, at the same time, under conditions of work with limited financial and material equipment. Work in Armenia provided the first experience that can be used for larger expeditions. On the basis of the good results using magnetometry and electromagnetic methods it is necessary to appeal for further research of this type as Armenia is very rich in historical monuments. In addition, it was the first measurement in Armenia at archaeological sites interpreted for prehistory and the Middle Ages as village settlements. Thus far, countless measurements have focused on prehistoric fortified sites. However, in addition to tourist attractions, these sites are threatened by unprofessional collection of historical artifacts and are also without protection against insensitive economic use of land (agriculture, industrial construction, etc.).

5. Conclusions Geophysical measurements proved to be beneficial even in urban, built-up terrains. For the reliability of such works, it is necessary to use a wider complex of geophysical methods (magnetometry, radar, ERT, DEMP, complex seismics and precise gravimetry are recommended). Magnetometry disturbed by the presence of engineering networks, iron objects (streetlights, cars, etc.) requires a modified processing procedure. It is recommended to subtract the measured data from the regional field and then work with residual anomalies. Further work is being done to clarify this methodology. A qualitative interpretation of geophysical anomalies is usually possible only in cooperation of a geophysicist with a given specialist (archaeologist, historian, and civil engineer). Geosciences 2020, 10, 356 25 of 26

Most of the measurements found underground were archaeological structures. Their interpretation and chronology are only probable without subsequent archaeological discovery. However, geophysical findings allow the identified structures to be focused on directly without their laborious search, possibly to select those that promise interesting results. For introductory work in developing countries (such as Armenia), a narrow complex of geophysical methods with instruments that do not require a large number of workers can be recommended. After obtaining basic knowledge from the site of interest, a more detailed project can be prepared. Armenia has a large number of archaeological sites, from prehistoric to early medieval. This is a great cultural asset, but it is often insufficiently legally protected from devastation. Continuation of work in Armenia could contribute to the protection of monuments in this regard (construction of a protected tourist site, etc.).

Author Contributions: Conceptualization, J.B. and J.F.; methodology, J.B., J.J. and T.B.; software, T.F.; validation, J.B. and J.F.; investigation, J.J. and J.B.; data curation, J.J. and T.B.; writing—original draft preparation, J.B. and J.J.; writing—review and editing, J.B., J.J. and J.F.; supervision, J.F.; project administration, J.B. All authors have read and agreed to the published version of the manuscript. Funding: This research received external funding of the Municipality of Prague, the Czech Development Agency and the Chironium Ltd. Company. Acknowledgments: We would like to express our thanks to the Municipality of Prague for financial support of our geophysical activities in Prague. We would like to express our thanks to the Czech Development Agency for financial support of our geophysical activities in Armenia. We would like to express our thanks to the Institute of Archaeology and Ethnography of the National Academy of Sciences of the Republic of Armenia for support of our geophysical activities in Armenia. We would like to express our thanks to the Chironium Ltd. Company for the financial support of the Apostolus project. We would like to express our thanks to TSK Praha a. s. (Road Authority of Prague) for actual technical information of the Old Town Square, HradˇcanySquare and Lesser Town Square. We also thank to our colleagues from the Institute of Archaeology in Prague for reasonable cooperation, technical advising and selflessness. Conflicts of Interest: The authors declare no conflict of interest.

References

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