Discovery mapping and interpretation of buried cultural resources non-invasively with ground-

penetrating radar

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IOP PUBLISHING JOURNAL OF GEOPHYSICS AND ENGINEERING

J Geophys Eng 8 (2011) S13ndashS22 doi1010881742-213283S02

Discovery mapping and interpretation ofburied cultural resources non-invasivelywith ground-penetrating radarLawrence B Conyers

Department of Anthropology University of Denver 2000 E Asbury St Denver CO 80208 USA

E-mail lconyersduedu

Received 23 October 2010Accepted for publication 11 February 2011Published 23 August 2011Online at stacksioporgJGE8S13

AbstractGround-penetrating radar is an extremely useful tool for the mapping and interpretation ofburied cultural remains within 2ndash3 metres of the surface especially when the stratigraphy iscomplex Standard reflection profiles can be processed to correct for depth and distance andalso filtered and processed to make cultural features visible When many profiles are collectedin closely spaced transects in a grid reflections can be re-sampled and displayed in amplitudeslice-maps and isosurface renderings to make buried features visible Sometimes howeverthe abundance and complexity of subsurface reflections is so complex that each individualprofile must be interpreted manually which necessitates an understanding of radar wavepropagation reflection refraction and attenuation in the ground In order to differentiatereflections from cultural features this understanding of radar energy must be merged with anunderstanding of the chemistry of the ground soil and geological stratigraphy and how thosevariables affect radar reflections When taken as a package of visualization tools GPR can beused as an effective tool for interpreting aspects of history and culture at buried sites in waysnot possible using traditional archaeological methods

Keywords ground-penetrating radar cultural resources

(Some figures in this article are in colour only in the electronic version)

Introduction

Ground-penetrating radar (GPR) is a near-surface geophysicaltechnique that allows scientists to discover and map buriedcultural features in ways not possible using traditional fieldmethods It is the most widely used near-surface geophysicalmethod to produce three-dimensional images and maps ofthe ground The method consists of measuring the elapsedtime between when pulses of radar energy are transmittedfrom a surface antenna reflected from buried discontinuitiesand then received back at the surface When the distributionand orientation of those subsurface reflections can be relatedto aspects of buried cultural features such as the presenceof buried architecture human use areas or other associatedremains high definition three-dimensional maps and otherimages of buried sites can be produced GPR is a near-surface

geophysical technique that is most effective with buried siteswhere artefacts and features of interest are located within 2ndash3 m of the surface but has occasionally been used for moredeeply buried deposits

A growing community of archaeologists has beenincorporating GPR as a routine non-invasive field procedure(Conyers 2004a Gaffney and Gater 2003) Their maps andimages can act as primary data that can be used to guide theplacement of excavations define sensitive areas containingcultural remains to avoid place archaeological sites within abroader environmental context and study human interactionwith and adaptation to ancient landscapes (Conyers 2010Conyers and Leckebusch 2010 Kvamme 2003)

Usually in archaeological GPR studies radar antennas aremoved along the ground in transects and two-dimensionalprofiles of a large number of reflections at various depths

1742-213211030013+10$3300 copy 2011 Nanjing Geophysical Research Institute Printed in the UK S13

L B Conyers

Figure 1 GPR reflection profile of Roman remains at AshkelonIsrael When profiles cross walls perpendicularly point-sourcereflection profiles are produced and when they parallel lines the topof the wall produces a complex series of high amplitude planar andpoint-source reflections

are created producing profiles of subsurface stratigraphyand buried archaeological features along lines (figure 1)Many closely spaced two-dimensional profiles within a gridcan then be processed to produce horizontal amplitude slicemaps (figure 2) and isosurface renderings (figure 3) thatproduce images of reflections of certain amplitudes in three-dimensional space Recently systems have been developedthat can simultaneously transmit and receive from numerousantennas in an array which are still in the developmental

Figure 2 Many reflection profiles can be processed into horizontal slices with the placement of reflection amplitudes coloured rainbowshades This map of an Inca site from Ecuador shows the location of adobe and stone walls of a royal residence enclosure Each slice isdefined in two-way travel times in nanoseconds which can be converted to depth when velocities are calculated

stage but which have the potential of producing even moreaccurate three-dimensional images (Conyers and Leckebusch2010 Leckebusch and Rychener 2007 Leckebusch et al2008)

While three-dimensional images are often effectiveat producing interesting and useful images when buriedarchaeological features produce distinct reflections within asomewhat homogeneous matrix (figures 2 and 3) Howeverwhen associated stratigraphy is complex each of the individualreflection profiles must be analysed individually Many GPRpractitioners have recently tended to rely a great deal on slicemaps and isosurface images as they simplify the hundredsand thousands of reflections within many profiles into a fewuseful images However the individual reflection profilesoften contain important information that can potentially befiltered out during the production of these slice maps andisosurfaces and therefore the profiles need to be individuallyanalysed also

There are a number of software programs that are usefulat making amplitude slice maps from numerous reflectionprofiles in a grid All GPR hardware manufacturers have theirown programs for this type of analysis each produced for theneeds of their customers Some are very good for pipe andutility location others for environmental and civil engineeringapplications and others for a wider variety of applicationsWhile the exact algorithms that are used in each are usuallynot available the results of the product of each can be viewedvisually Three amplitude maps of the same horizontal slice inthe ground using three different amplitude analysis programs

S14

Discovery mapping and interpretation of buried cultural resources with GPR

Figure 3 Isosurface image of the highest amplitude reflections from a pit-house floor preserved within sand dunes along the Oregon CoastUSA Random stones probably related to human activity that occurred in the dunes can be seen as small reflections scattered above andaround the buried house floor

Figure 4 Comparison of amplitude slice images from three different software programs with different re-sampling algorithms On the leftis GPR slice (httpwwwgpr-surveycom) the middle is GPR process (httpmysiteduedusimlconyer) and on the right is EKKO mapper(httpwwwsensoftca) The features in the image are circular bases of historic brick kilns in Ohio (data courtesy of Jarrod Burks)

are shown in figure 4 The three buried features visible inthe maps are the bases of historic kilns in Ohio USA whichgenerate very high amplitude reflections The image on the leftis very useful for identifying the features as a whole but tendsto average reflections somewhat The middle map producesan image of almost each and every brick within these featuresbut tends to produce less distinct overall maps The map onthe right is much less distinct in all respects and appears tohave produced a map of features that are not found in the otherimages for unknown reasons

Very much the same type of variation in the visualizingsoftware for reflection profiles is true for differing softwaremanufacturers (figure 5) The most important aspect forgenerating images of these profiles is the ability to changethe gains filter out noise adjust scales for depth (in timeand distance) and produce distance measurements along thetransect accurately Often archaeologists tend to bypass basicinterpretation of reflection profiles as these images tend tobe complex and sometimes difficult to interpret without adetailed understanding of what generates reflections in theground Accurate and useful profile interpretation ability only

comes with experience and knowledge of not only of how radarenergy moves reflects refracts and is attenuated in the groundbut also the background in soil and sediment stratigraphy andthe physical and chemical properties of the ground

As an example of the differences in software imagesthat are available figure 5 shows a standard output andthe same profile that has been processed in a way wherethe buried features are more visible The upper image hashad background noise removed but the axes have not beenmodified and the reflections gained to make the features morevisible and interpretable In the lower profile the distincthyperbolas which are individual graves are much more easilydistinguishable as reflection hyperbolas Shallow roots whichproduce the less distinct hyperbolas also become visible inthe lower profile

Complexities in the GPR method

The success of GPR surveys is to a great extent dependent onsoil and sediment mineralogy clay content ground moisturedepth of burial surface topography and vegetation (Conyers

S15

Discovery mapping and interpretation of buried cultural resources with GPR

Figure 3 Isosurface image of the highest amplitude reflections from a pit-house floor preserved within sand dunes along the Oregon CoastUSA Random stones probably related to human activity that occurred in the dunes can be seen as small reflections scattered above andaround the buried house floor

Figure 4 Comparison of amplitude slice images from three different software programs with different re-sampling algorithms On the leftis GPR slice (httpwwwgpr-surveycom) the middle is GPR process (httpmysiteduedusimlconyer) and on the right is EKKO mapper(httpwwwsensoftca) The features in the image are circular bases of historic brick kilns in Ohio (data courtesy of Jarrod Burks)

are shown in figure 4 The three buried features visible inthe maps are the bases of historic kilns in Ohio USA whichgenerate very high amplitude reflections The image on the leftis very useful for identifying the features as a whole but tendsto average reflections somewhat The middle map producesan image of almost each and every brick within these featuresbut tends to produce less distinct overall maps The map onthe right is much less distinct in all respects and appears tohave produced a map of features that are not found in the otherimages for unknown reasons

Very much the same type of variation in the visualizingsoftware for reflection profiles is true for differing softwaremanufacturers (figure 5) The most important aspect forgenerating images of these profiles is the ability to changethe gains filter out noise adjust scales for depth (in timeand distance) and produce distance measurements along thetransect accurately Often archaeologists tend to bypass basicinterpretation of reflection profiles as these images tend tobe complex and sometimes difficult to interpret without adetailed understanding of what generates reflections in theground Accurate and useful profile interpretation ability only

comes with experience and knowledge of not only of how radarenergy moves reflects refracts and is attenuated in the groundbut also the background in soil and sediment stratigraphy andthe physical and chemical properties of the ground

As an example of the differences in software imagesthat are available figure 5 shows a standard output andthe same profile that has been processed in a way wherethe buried features are more visible The upper image hashad background noise removed but the axes have not beenmodified and the reflections gained to make the features morevisible and interpretable In the lower profile the distincthyperbolas which are individual graves are much more easilydistinguishable as reflection hyperbolas Shallow roots whichproduce the less distinct hyperbolas also become visible inthe lower profile

Complexities in the GPR method

The success of GPR surveys is to a great extent dependent onsoil and sediment mineralogy clay content ground moisturedepth of burial surface topography and vegetation (Conyers

S15

L B Conyers

Figure 5 Comparison of reflection profiles produced from different software in a historic cemetery in Georgia USA The upper profileincludes the complete time window and has background removed but no re-gaining of the amplitudes The lower profile has had reflectionsre-gained and then spatially averaged within a smaller time window to make the reflection hyperbolas from burials more visible Shallowroots are also visible in the lower profile as low amplitude hyperbola reflections in the 5ndash6 ns time range

2004a p 28) While some studies suggest that GPR is onlysuccessful in areas where soils and underlying sediment aredry (Annan and Davis 1992) radar wave penetration willoccur in any type of ground that is not highly electricallyconductive (Conyers 2004b) Radar energy becomes bothdispersed and attenuated as it radiates into the ground Whenportions of the original transmitted waves are reflected backtowards the surface they will suffer additional attenuation bythe material through which they pass before finally beingrecorded at the surface Therefore to be detected as reflectionsimportant subsurface interfaces must not only have sufficientelectrical contrast at their boundary (which is what creates thereflections) but must also be located at a shallow enough depthwhere sufficient radar energy is still available for reflectionAs radar energy is propagated to increasing depths the energyalso becomes weaker as it spreads out over more surfacearea and is absorbed by the ground making less available forreflection

Post-acquisition frequency filtering and reflectionamplification techniques can sometimes be applied toreflection data after acquisition that will enhance some verylow amplitude reflections in order to make them more visiblebut in all ground conditions all radar energy is lost at a certaindepth and in certain materials The depth of complete energyattenuation is often difficult to predict in advance of a surveybut can be readily determined once antennas are moved overthe ground in a prospective area and the depth (as measuredin two-way radar travel time) of coherent reflected waves isdetermined While in some cases greater depth penetrationcan be obtained using lower frequency antennas often allradar energy is attenuated at a certain depth no matter whatfrequency antenna is used (Conyers 2004a)

The complexity of radar travel paths in the ground isan additional variable that is sometimes difficult to predictin advance and also interpret in GPR reflection profiles oncedata are visible in amplitude slice maps and isosurface images

Figure 6 Reflection profile crossing a prehistoric irrigation canal insouthern Arizona The highest amplitude reflections are generatedfrom the base of the canal while the edges of the canal are loweramplitude reflections that are difficult to discern from thebackground

Radar waves not only are transmitted in the ground in a conicalpattern from the surface antenna but will also be reflectedand refracted in complex ways when interfaces of differentthickness and orientation are encountered An example of thiscomplexity is a prehistoric irrigation canalrsquos edges which areonly faintly visible in a reflection profile (figure 6) The highestamplitudes are generated from the base of the channel becausea layer of mud was deposited there in a small lsquobowl-shapedlayerrsquo which acted as a highly reflective focusing surfaceThis interface is displayed as a point-source radar reflectorthat generated a very distinct series of hyperbolic-shapedreflections The edges of the channel itself produce onlyvery faint reflections because sediment of similar chemicaland physical properties occurs in the both the channel fill

S16

Discovery mapping and interpretation of buried cultural resources with GPR

Figure 7 Amplitude slice map of prehistoric irrigation canals insouthern Arizona USA Changes in the sediment types preserved inthe base of the channels are producing changes in radar reflectionamplitudes along the canals Associated small feeder canals andagricultural fields are also visible

and the adjacent material In addition the channel edgesdip in a way such that much of the radar energy that strikesthem is reflected away from the surface-receiving antennaand therefore not recorded If many profiles in a grid wereprocessed into amplitude slice maps the channel (that is thetarget of the GPR survey) would tend to be obscured bythe high amplitude reflections that were produced from onlythe base of the channel The high amplitude reflectionsvisible in an amplitude slice map will mimic the location ofthe channel but they are recorded in the time window belowthe base of the channel itself Also as only the high amplitudesare usually mapped in slice maps the image of the channelactually displays changes in the sediment types preservedin the base of the channel not the channel itself (figure 7)An understanding of what has produced the reflections wouldtherefore be necessary before an accurate interpretation of the

amplitude maps is possible The slice maps are still accuratelymapping portions of the channels but it is actually changes inthe sediment types preserved in the base of the channel thatare being displayed and those are recorded below the actualdepth (as recorded in time) of the canal

As a way to help understand or predict in advancehow radar energy will move in the ground and what typesof reflections might be recorded predictive models can beproduced (figure 8) These models (Goodman 1994) takeinto account the electrical properties of the ground andarchaeological features as well as their orientation and radarfrequency and transmission geometry in two dimensionsThe resulting models can be extraordinarily helpful ininterpretation as they can generate images of what reflectionswould be produced from those features in the ground giventhose parameters and a view of their orientation and recordedtime Those models can then be used as a guide to whatequipment should be used and the collection parameters priorto going to the field and also for interpreting and processingreflection profiles after collection (figure 8) When thismodelling procedure was conducted in Tunisia the ceilingand floor of an underground church can be seen as highamplitude reflections while the vertical walls are modelled asinvisible The ceiling produces a very prominent reflection andis accurately located in space while the model shows that theflat floor would produce an upward bowing reflection due to thelsquopull uprsquo created by faster velocities of waves travelling withinthe overlying void space The reflection profiles collectedin the field showed almost exactly what the model predicted(figure 8)

Processing and interpretation methods for complexsites

Surface topography and the subsurface orientation of featuresand stratigraphy of a site may sometimes necessitate theconstruction of slices that are neither uniform in thicknessnor horizontal (Conyers 2004a 2010) At the site of Petrain Jordan much is known about the late Nabataean andRoman occupation of this impressive desert valley the remainsof which are located within 2 m of the ground surface(figure 9) There is also subtle and potentially importantevidence of an earlier occupation of the valley prior to thistime by people who originally lived in much more humbledwellings These structures were likely razed and covered overduring the first-century urbanization episode which created acity layout that can be seen at or near the surface of Petratoday (Conyers 2010) One site at Petra was tested with GPRto look at the deepest architectural remains below about 2 mdepth (Conyers et al 2002) Reflection profiles within thegrid show a very subtle sloping reflection that is correlativeto an ancient living surface visible in nearby excavationsThis reflection was hypothesized to have been generated fromthe living surface on the valley floor prior to the first-centuryurbanization construction episode

In order to produce images of the buried surface andremaining features built on it the amplitudes of all GPRreflections in all profiles within the grid were digitized gridded

S17

L B Conyers

Figure 8 Synthetic reflection profile generation of an underground church in Tunisia (httpwwwgpr-surveycomgprsimhtml) Only theceiling floor and walls of the church were simulated producing reflections that accurately depicted the upward bowing ceiling and apronounced upward bowing floor The floor reflection distortion is created by a velocity lsquopull uprsquo as energy is transmitted at the speed oflight within the church cavity but at much slower rates elsewhere in the ground The walls are invisible as transmitted energy is passedparallel to them and if reflections occurred the resulting waves were transmitted away from the surface antennas and not recorded

Figure 9 Reflection profile showing the subtle reflection surface with variable amplitudes under first-century fill

and mapped in slices parallel to this sloping surface (figure 10)The highest amplitude reflections correspond to either standingarchitecture or architectural rubble on and directly above thisburied surface Areas with no significant reflection are openspaces or pathways between buildings on that pre-first-centurysurface This type of GPR analysis produces horizon-specificmaps showing the remains of simple buildings (Conyers 2010)and possible pathways between them The pathways areidentifiable as linear zones of no reflection which led from thehighlands to the south towards the water drainage to the north(figure 10) The orientations of early buildings along thesepathways show that they were built in various orientations andlikely placed on land that was suitable for building at that timeThis type of informal construction likely functioned only aspart-time living quarters Only later in the late first century BC

when the Nabataeans had established control over trade routesfrom south Arabia to the eastern Mediterranean did socialdifferentiation and monumental construction take place Theremains of these later more formal buildings (figure 10) fromthat construction period are in stark contrast to these earliesthabitations In the upper GPR slice the structures withinwhat became a formal garden were invariably oriented tothe cardinal directions consistent with Hellenistic influencedbuilding practices from later Nabataean times

In deep and stratigraphically complex areas amplitudemaps and isosurface images are of little value as slices willoften cross-cut reflections or those reflections will clutterisosurfaces creating distorted and inaccurate images Whenthis is the case only manual interpretation of each individualreflection profile can produce accurate interpretations

S18

Discovery mapping and interpretation of buried cultural resources with GPR

Figure 7 Amplitude slice map of prehistoric irrigation canals insouthern Arizona USA Changes in the sediment types preserved inthe base of the channels are producing changes in radar reflectionamplitudes along the canals Associated small feeder canals andagricultural fields are also visible

and the adjacent material In addition the channel edgesdip in a way such that much of the radar energy that strikesthem is reflected away from the surface-receiving antennaand therefore not recorded If many profiles in a grid wereprocessed into amplitude slice maps the channel (that is thetarget of the GPR survey) would tend to be obscured bythe high amplitude reflections that were produced from onlythe base of the channel The high amplitude reflectionsvisible in an amplitude slice map will mimic the location ofthe channel but they are recorded in the time window belowthe base of the channel itself Also as only the high amplitudesare usually mapped in slice maps the image of the channelactually displays changes in the sediment types preservedin the base of the channel not the channel itself (figure 7)An understanding of what has produced the reflections wouldtherefore be necessary before an accurate interpretation of the

amplitude maps is possible The slice maps are still accuratelymapping portions of the channels but it is actually changes inthe sediment types preserved in the base of the channel thatare being displayed and those are recorded below the actualdepth (as recorded in time) of the canal

As a way to help understand or predict in advancehow radar energy will move in the ground and what typesof reflections might be recorded predictive models can beproduced (figure 8) These models (Goodman 1994) takeinto account the electrical properties of the ground andarchaeological features as well as their orientation and radarfrequency and transmission geometry in two dimensionsThe resulting models can be extraordinarily helpful ininterpretation as they can generate images of what reflectionswould be produced from those features in the ground giventhose parameters and a view of their orientation and recordedtime Those models can then be used as a guide to whatequipment should be used and the collection parameters priorto going to the field and also for interpreting and processingreflection profiles after collection (figure 8) When thismodelling procedure was conducted in Tunisia the ceilingand floor of an underground church can be seen as highamplitude reflections while the vertical walls are modelled asinvisible The ceiling produces a very prominent reflection andis accurately located in space while the model shows that theflat floor would produce an upward bowing reflection due to thelsquopull uprsquo created by faster velocities of waves travelling withinthe overlying void space The reflection profiles collectedin the field showed almost exactly what the model predicted(figure 8)

Processing and interpretation methods for complexsites

Surface topography and the subsurface orientation of featuresand stratigraphy of a site may sometimes necessitate theconstruction of slices that are neither uniform in thicknessnor horizontal (Conyers 2004a 2010) At the site of Petrain Jordan much is known about the late Nabataean andRoman occupation of this impressive desert valley the remainsof which are located within 2 m of the ground surface(figure 9) There is also subtle and potentially importantevidence of an earlier occupation of the valley prior to thistime by people who originally lived in much more humbledwellings These structures were likely razed and covered overduring the first-century urbanization episode which created acity layout that can be seen at or near the surface of Petratoday (Conyers 2010) One site at Petra was tested with GPRto look at the deepest architectural remains below about 2 mdepth (Conyers et al 2002) Reflection profiles within thegrid show a very subtle sloping reflection that is correlativeto an ancient living surface visible in nearby excavationsThis reflection was hypothesized to have been generated fromthe living surface on the valley floor prior to the first-centuryurbanization construction episode

In order to produce images of the buried surface andremaining features built on it the amplitudes of all GPRreflections in all profiles within the grid were digitized gridded

S17

L B Conyers

Figure 8 Synthetic reflection profile generation of an underground church in Tunisia (httpwwwgpr-surveycomgprsimhtml) Only theceiling floor and walls of the church were simulated producing reflections that accurately depicted the upward bowing ceiling and apronounced upward bowing floor The floor reflection distortion is created by a velocity lsquopull uprsquo as energy is transmitted at the speed oflight within the church cavity but at much slower rates elsewhere in the ground The walls are invisible as transmitted energy is passedparallel to them and if reflections occurred the resulting waves were transmitted away from the surface antennas and not recorded

Figure 9 Reflection profile showing the subtle reflection surface with variable amplitudes under first-century fill

and mapped in slices parallel to this sloping surface (figure 10)The highest amplitude reflections correspond to either standingarchitecture or architectural rubble on and directly above thisburied surface Areas with no significant reflection are openspaces or pathways between buildings on that pre-first-centurysurface This type of GPR analysis produces horizon-specificmaps showing the remains of simple buildings (Conyers 2010)and possible pathways between them The pathways areidentifiable as linear zones of no reflection which led from thehighlands to the south towards the water drainage to the north(figure 10) The orientations of early buildings along thesepathways show that they were built in various orientations andlikely placed on land that was suitable for building at that timeThis type of informal construction likely functioned only aspart-time living quarters Only later in the late first century BC

when the Nabataeans had established control over trade routesfrom south Arabia to the eastern Mediterranean did socialdifferentiation and monumental construction take place Theremains of these later more formal buildings (figure 10) fromthat construction period are in stark contrast to these earliesthabitations In the upper GPR slice the structures withinwhat became a formal garden were invariably oriented tothe cardinal directions consistent with Hellenistic influencedbuilding practices from later Nabataean times

In deep and stratigraphically complex areas amplitudemaps and isosurface images are of little value as slices willoften cross-cut reflections or those reflections will clutterisosurfaces creating distorted and inaccurate images Whenthis is the case only manual interpretation of each individualreflection profile can produce accurate interpretations

S18

L B Conyers

Figure 8 Synthetic reflection profile generation of an underground church in Tunisia (httpwwwgpr-surveycomgprsimhtml) Only theceiling floor and walls of the church were simulated producing reflections that accurately depicted the upward bowing ceiling and apronounced upward bowing floor The floor reflection distortion is created by a velocity lsquopull uprsquo as energy is transmitted at the speed oflight within the church cavity but at much slower rates elsewhere in the ground The walls are invisible as transmitted energy is passedparallel to them and if reflections occurred the resulting waves were transmitted away from the surface antennas and not recorded

Figure 9 Reflection profile showing the subtle reflection surface with variable amplitudes under first-century fill

and mapped in slices parallel to this sloping surface (figure 10)The highest amplitude reflections correspond to either standingarchitecture or architectural rubble on and directly above thisburied surface Areas with no significant reflection are openspaces or pathways between buildings on that pre-first-centurysurface This type of GPR analysis produces horizon-specificmaps showing the remains of simple buildings (Conyers 2010)and possible pathways between them The pathways areidentifiable as linear zones of no reflection which led from thehighlands to the south towards the water drainage to the north(figure 10) The orientations of early buildings along thesepathways show that they were built in various orientations andlikely placed on land that was suitable for building at that timeThis type of informal construction likely functioned only aspart-time living quarters Only later in the late first century BC

when the Nabataeans had established control over trade routesfrom south Arabia to the eastern Mediterranean did socialdifferentiation and monumental construction take place Theremains of these later more formal buildings (figure 10) fromthat construction period are in stark contrast to these earliesthabitations In the upper GPR slice the structures withinwhat became a formal garden were invariably oriented tothe cardinal directions consistent with Hellenistic influencedbuilding practices from later Nabataean times

In deep and stratigraphically complex areas amplitudemaps and isosurface images are of little value as slices willoften cross-cut reflections or those reflections will clutterisosurfaces creating distorted and inaccurate images Whenthis is the case only manual interpretation of each individualreflection profile can produce accurate interpretations

S18

Discovery mapping and interpretation of buried cultural resources with GPR

Figure 10 Example of an amplitude slice-map showing columns and walls of a buried late-Nabataean temple at Petra Jordan The slice onthe left is showing the buildings constructed on the fill after the first-century urbanization project On the right (deeper slice) is the image offeatures built on the living surface prior to the filling episode

Figure 11 Reflection profile using the 400 MHz antennas in front of a rock shelter in Queensland Australia Bedrock and tree roots arevisible as planar and hyperbolic reflections respectively Probable cultural features such as the distinct planar floor or work surface werealso visible in individual profiles

A large grid of reflection profiles was collected in frontof a rock shelter in Queensland Australia The area mappedappears from its surface expression to be a small basin thatwould have collected not only naturally deposited sedimentbut also remains of a very long human occupation spanning asmany as 30 000 years Reflection profiles were quite complexbut a very high amplitude reflection from the sandstonebedrock was visible (figure 11) Core holes confirmed theorigin of this reflection and allowed for accurate timendashdepth

conversions Many shallow tree roots were visible in allprofiles and could be ignored during interpretation Theorigin of other reflections above the bedrock is speculativebut is likely hard-packed floors or work surfaces (figure 11) infront of the rock shelter

A map of the depth to bedrock in this small basin in frontof the shelter was possible but only after velocity analysis hadconverted all radar travel times to depth and each individualprofile was interpreted (figure 12) This image shows bedrock

S19

L B Conyers

Figure 12 Depth to bedrock map at a rock shelter in QueenslandAustralia produced from interpreting individual reflection profilesin a large grid

Figure 13 Reflection profile from the Oregon Coast USA showinghyperbolic reflections from roots and animal burrows but also ahigh amplitude planar reflection from a pit house Many profiles ofthis sort within a grid were used to create the isosurface image infigure 14

protuberances and the edge of the basin and small sub-basinsthat might contain sites of varying ages In this case only adetailed analysis of each individual profile in the grid allowedfor the production of this map of the small natural basin infront of the rock shelter

When many closely spaced reflection profiles arecollected in a grid the amount of information in everyprofile can be overwhelming in terms of mapping featuresin the ground in a timely fashion When this is the casethe amplitudes of reflected waves in all profiles in a grid canbe visualized in an isosurface and certain amplitudes illustratedand shaded with artificial sunlight in order to produce imagesof buried features Figure 13 shows reflection profiles

collected using the 900 MHz antennas in transects spaced only20 cm apart each of which showed many reflections from rootsand animal burrows Within these complex reflections was aplanar reflection that was produced from some features in apit house In any one profile this feature could be identified ascultural but its actual shape in three dimensions was difficultto discern

All reflection profiles within the grid were then sampledand only the high amplitude reflections were coloured andshaded to produce an isosurface image (figure 14) Thisimage illustrates only the very high amplitudes and shows twoedges of the pit feature that are composed of very differentmaterial from the matrix of the site These appear to belsquobenchesrsquo or work areas within the structure which werenot immediately visible in individual reflection profiles Theutility of producing these types of images from many profilesthat record reflections in three-dimensional space is apparent

There are times when the highest amplitude radarreflections are not the target of a GPR survey but instead areasof no reflection are important In southern Arizona the ancientHohokam people who inhabited the area from about AD 200to 1400 constructed many buildings from compacted adobeThe mud used to construct the adobe walls was usually quarriedvery near where the buildings were constructed and thereforethere is often little if any chemical or physical differencebetween the architectural features and the surrounding groundAs a result walls bounded by undisturbed sediments and soilhave no lithological changes that would reflect radar wavesAt best walls are visible as areas of no reflection at all becausethe adobe mixture used to construct them were homogenizedduring their construction In addition the adobe often containsa high amount of clay When moist this material can attenuateradar energy that is transmitted through it creating areas of noreflection when visible in GPR reflection profiles (figure 15)

As these adobe walls deteriorated and were eroded overtime the mud tended to lsquomeltrsquo adjacent to the walls duringrainstorms Between melting episodes wind-blown sand andsilt were deposited which produced interbedded layers ofadobe melt and coarser sediment adjacent to the lower portionof the walls that remained standing The melt-sediment layersproduce sedimentary layers that are capable of reflecting highamplitude radar energy These layers adjacent to the wallsproduced high amplitude sloping reflections which are visiblein profiles (figure 15) In this case areas of no reflectionbounded by high amplitude reflections indicate the presenceof adobe walls with the areas of no reflection being the actualwalls of interest

When many GPR reflection profiles are sliced and viewedin horizontal slices the high and low amplitudes are visible andcan be used to map the location of the walls (figure 16) In thiscase the areas of high amplitude contain the remains of wallsthat have eroded over time and the areas of no reflection arethe intact walls themselves

GPR technology to test ideas about the human past

An important re-direction in the use of geophysics forarchaeology is the GPR methodrsquos ability to test cultural models

S20

Discovery mapping and interpretation of buried cultural resources with GPR

Figure 14 Isosurface image of benches or work areas within a pit house on the Oregon Coast USA In this image only the highestamplitudes of the reflections were used to create the image

Figure 15 Reflection profile that crosses an adobe wall ofcompacted mud The wall is non-reflective because it is composedof homogenized clay-rich material which has no boundaries thatwould reflect radar energy Its composition also attenuates energyproducing areas of no reflection

about the human past Most archaeological geophysics is stillfocused on its application of finding buried objects or featuresthat can later be excavated using traditional archaeologicalmethods The GPR processing and image production methodsillustrated here are becoming routine and most practitionerscan now produce accurate three-dimensional images of theground If they are correctly interpreted GPR images cannow be used to test hypotheses about human activity suchas social organization and other anthropological questionsFor instance if models of historic human activity can berelated to the placement orientation shape and clustering ofburied architecture then GPR mapping is capable of accuratelytesting these hypotheses or developing new ideas about thepast (Conyers 2010 Conyers and Osburn 2006) In this wayGPR can potentially tell a great deal about archaeological siteswithout ever having to excavate which will be of great benefitin the future as traditional archaeological digging becomesmore expensive and is often curtailed due to preservationissues

Figure 16 Amplitude slice map that shows adobe walls as areas ofno reflection bounded by layers of eroded adobe from the wallsinterbedded by wind blown sand The eroded areas are highlyreflective as these interfaces produce a good deal of radar energyreflection

Conclusions

Ground-penetrating radar has the unique ability of near-surfacegeophysical methods to produce three-dimensional maps andimages of buried architecture and other associated cultural andnatural features for landscape analysis Using high-definitiontwo-dimensional reflection profiles three-dimensional maps

S21

L B Conyers

of amplitude changes can define physical and chemicalchanges in the ground that are related to the cultural materialsof importance When these data and maps are used to test ideasabout human activities of all sorts they offer a powerful andtime-efficient way to study ancient human behaviour socialorganization and other important archaeological concepts

In the processing of GPR reflection data maps and imagesmust be generated and then integrated with information aboutsediments soils and the geometry and composition of buriedcultural features in order to make accurate interpretationsabout what is preserved in the ground This can be done byplacing these cultural data from excavations within horizontalamplitude maps that produce images of only certain amplitudeswithin a three-dimensional volume of radar reflections whichmight be high amplitudes from important buried features butalso could be areas of no reflection at all In some casesonly a detailed analysis of reflection profiles can differentiatenatural geological layers from cultural features especiallywhen the ground contains an abundance of reflections Inall cases the results of GPR reflection images must beidentified and mapped spatially in the ground When multipleimages that are both two and three dimensional in view areinterpreted they can provide a powerful tool for the integrationof archaeological sites within what are often complex groundconditions

References

Annan A P and Davis J L 1992 Design and development of a digitalground penetrating radar system Ground Penetrating Radar

ed J A Pilon (Ottowa Canada Geological Surveyof Canada) Geological Survey of Canada Paper 90-4pp 49ndash55

Conyers L B 2004a Ground-penetrating Radar for Archaeology(Walnut Creek CA Altamira Press)

Conyers L B 2004b Moisture and soil differences as related to thespatial accuracy of amplitude maps at two archaeological testsites Proc 10th Int Conf on Ground Penetrating Radar (DelftThe Netherlands 21 June 2004) pp 67ndash72

Conyers L B 2010 Ground-penetrating radar for anthropologicalresearch Antiquity 84 175ndash84

Conyers L B Ernenwein Eileen G and Leigh-Ann B 2002Ground-penetrating radar discovery at Petra Jordan Antiquity76 339ndash40

Conyers L B and Leckebusch J 2010 Geophysical archaeologyresearch agendas for the future some ground-penetrating radarexamples Archaeol Prospect 17 117ndash23

Conyers L B and Osburn T 2006 GPR Mapping to testanthropological hypotheses a study from comb wash UtahAmerican Southwest Proc 11th Int Conf onGround-penetrating Radar (Columbus OH USA 19ndash22 June2006) pp 245ndash9

Gaffney C and Gater J 2003 Revealing the Buried Past Geophysicsfor Archaeologists (Stroud UK Tempus)

Goodman D 1994 Ground-penetrating radar simulationin engineering and archaeology Geophysics59 224ndash32

Kvamme K L 2003 Geophysical surveys as landscape archaeologyAm Antiquity 63 435ndash57

Leckebusch J and Rychener J 2007 Verification and topographiccorrection of GPR data in three dimensions Near SurfGeophys 5 395ndash403

Leckebusch J Weibel A and Buhler F 2008 Semi-automaticfeature extraction from GPR data Near Surf Geophys6 75ndash84

S22

L B Conyers

Figure 12 Depth to bedrock map at a rock shelter in QueenslandAustralia produced from interpreting individual reflection profilesin a large grid

Figure 13 Reflection profile from the Oregon Coast USA showinghyperbolic reflections from roots and animal burrows but also ahigh amplitude planar reflection from a pit house Many profiles ofthis sort within a grid were used to create the isosurface image infigure 14

protuberances and the edge of the basin and small sub-basinsthat might contain sites of varying ages In this case only adetailed analysis of each individual profile in the grid allowedfor the production of this map of the small natural basin infront of the rock shelter

When many closely spaced reflection profiles arecollected in a grid the amount of information in everyprofile can be overwhelming in terms of mapping featuresin the ground in a timely fashion When this is the casethe amplitudes of reflected waves in all profiles in a grid canbe visualized in an isosurface and certain amplitudes illustratedand shaded with artificial sunlight in order to produce imagesof buried features Figure 13 shows reflection profiles

collected using the 900 MHz antennas in transects spaced only20 cm apart each of which showed many reflections from rootsand animal burrows Within these complex reflections was aplanar reflection that was produced from some features in apit house In any one profile this feature could be identified ascultural but its actual shape in three dimensions was difficultto discern

All reflection profiles within the grid were then sampledand only the high amplitude reflections were coloured andshaded to produce an isosurface image (figure 14) Thisimage illustrates only the very high amplitudes and shows twoedges of the pit feature that are composed of very differentmaterial from the matrix of the site These appear to belsquobenchesrsquo or work areas within the structure which werenot immediately visible in individual reflection profiles Theutility of producing these types of images from many profilesthat record reflections in three-dimensional space is apparent

There are times when the highest amplitude radarreflections are not the target of a GPR survey but instead areasof no reflection are important In southern Arizona the ancientHohokam people who inhabited the area from about AD 200to 1400 constructed many buildings from compacted adobeThe mud used to construct the adobe walls was usually quarriedvery near where the buildings were constructed and thereforethere is often little if any chemical or physical differencebetween the architectural features and the surrounding groundAs a result walls bounded by undisturbed sediments and soilhave no lithological changes that would reflect radar wavesAt best walls are visible as areas of no reflection at all becausethe adobe mixture used to construct them were homogenizedduring their construction In addition the adobe often containsa high amount of clay When moist this material can attenuateradar energy that is transmitted through it creating areas of noreflection when visible in GPR reflection profiles (figure 15)

As these adobe walls deteriorated and were eroded overtime the mud tended to lsquomeltrsquo adjacent to the walls duringrainstorms Between melting episodes wind-blown sand andsilt were deposited which produced interbedded layers ofadobe melt and coarser sediment adjacent to the lower portionof the walls that remained standing The melt-sediment layersproduce sedimentary layers that are capable of reflecting highamplitude radar energy These layers adjacent to the wallsproduced high amplitude sloping reflections which are visiblein profiles (figure 15) In this case areas of no reflectionbounded by high amplitude reflections indicate the presenceof adobe walls with the areas of no reflection being the actualwalls of interest

When many GPR reflection profiles are sliced and viewedin horizontal slices the high and low amplitudes are visible andcan be used to map the location of the walls (figure 16) In thiscase the areas of high amplitude contain the remains of wallsthat have eroded over time and the areas of no reflection arethe intact walls themselves

GPR technology to test ideas about the human past

An important re-direction in the use of geophysics forarchaeology is the GPR methodrsquos ability to test cultural models

S20

Discovery mapping and interpretation of buried cultural resources with GPR

Figure 14 Isosurface image of benches or work areas within a pit house on the Oregon Coast USA In this image only the highestamplitudes of the reflections were used to create the image

Figure 15 Reflection profile that crosses an adobe wall ofcompacted mud The wall is non-reflective because it is composedof homogenized clay-rich material which has no boundaries thatwould reflect radar energy Its composition also attenuates energyproducing areas of no reflection

about the human past Most archaeological geophysics is stillfocused on its application of finding buried objects or featuresthat can later be excavated using traditional archaeologicalmethods The GPR processing and image production methodsillustrated here are becoming routine and most practitionerscan now produce accurate three-dimensional images of theground If they are correctly interpreted GPR images cannow be used to test hypotheses about human activity suchas social organization and other anthropological questionsFor instance if models of historic human activity can berelated to the placement orientation shape and clustering ofburied architecture then GPR mapping is capable of accuratelytesting these hypotheses or developing new ideas about thepast (Conyers 2010 Conyers and Osburn 2006) In this wayGPR can potentially tell a great deal about archaeological siteswithout ever having to excavate which will be of great benefitin the future as traditional archaeological digging becomesmore expensive and is often curtailed due to preservationissues

Figure 16 Amplitude slice map that shows adobe walls as areas ofno reflection bounded by layers of eroded adobe from the wallsinterbedded by wind blown sand The eroded areas are highlyreflective as these interfaces produce a good deal of radar energyreflection

Conclusions

Ground-penetrating radar has the unique ability of near-surfacegeophysical methods to produce three-dimensional maps andimages of buried architecture and other associated cultural andnatural features for landscape analysis Using high-definitiontwo-dimensional reflection profiles three-dimensional maps

S21

L B Conyers

of amplitude changes can define physical and chemicalchanges in the ground that are related to the cultural materialsof importance When these data and maps are used to test ideasabout human activities of all sorts they offer a powerful andtime-efficient way to study ancient human behaviour socialorganization and other important archaeological concepts

In the processing of GPR reflection data maps and imagesmust be generated and then integrated with information aboutsediments soils and the geometry and composition of buriedcultural features in order to make accurate interpretationsabout what is preserved in the ground This can be done byplacing these cultural data from excavations within horizontalamplitude maps that produce images of only certain amplitudeswithin a three-dimensional volume of radar reflections whichmight be high amplitudes from important buried features butalso could be areas of no reflection at all In some casesonly a detailed analysis of reflection profiles can differentiatenatural geological layers from cultural features especiallywhen the ground contains an abundance of reflections Inall cases the results of GPR reflection images must beidentified and mapped spatially in the ground When multipleimages that are both two and three dimensional in view areinterpreted they can provide a powerful tool for the integrationof archaeological sites within what are often complex groundconditions

References

Annan A P and Davis J L 1992 Design and development of a digitalground penetrating radar system Ground Penetrating Radar

ed J A Pilon (Ottowa Canada Geological Surveyof Canada) Geological Survey of Canada Paper 90-4pp 49ndash55

Conyers L B 2004a Ground-penetrating Radar for Archaeology(Walnut Creek CA Altamira Press)

Conyers L B 2004b Moisture and soil differences as related to thespatial accuracy of amplitude maps at two archaeological testsites Proc 10th Int Conf on Ground Penetrating Radar (DelftThe Netherlands 21 June 2004) pp 67ndash72

Conyers L B 2010 Ground-penetrating radar for anthropologicalresearch Antiquity 84 175ndash84

Conyers L B Ernenwein Eileen G and Leigh-Ann B 2002Ground-penetrating radar discovery at Petra Jordan Antiquity76 339ndash40

Conyers L B and Leckebusch J 2010 Geophysical archaeologyresearch agendas for the future some ground-penetrating radarexamples Archaeol Prospect 17 117ndash23

Conyers L B and Osburn T 2006 GPR Mapping to testanthropological hypotheses a study from comb wash UtahAmerican Southwest Proc 11th Int Conf onGround-penetrating Radar (Columbus OH USA 19ndash22 June2006) pp 245ndash9

Gaffney C and Gater J 2003 Revealing the Buried Past Geophysicsfor Archaeologists (Stroud UK Tempus)

Goodman D 1994 Ground-penetrating radar simulationin engineering and archaeology Geophysics59 224ndash32

Kvamme K L 2003 Geophysical surveys as landscape archaeologyAm Antiquity 63 435ndash57

Leckebusch J and Rychener J 2007 Verification and topographiccorrection of GPR data in three dimensions Near SurfGeophys 5 395ndash403

Leckebusch J Weibel A and Buhler F 2008 Semi-automaticfeature extraction from GPR data Near Surf Geophys6 75ndash84

S22

Discovery mapping and interpretation of buried cultural resources with GPR

Figure 14 Isosurface image of benches or work areas within a pit house on the Oregon Coast USA In this image only the highestamplitudes of the reflections were used to create the image

Figure 15 Reflection profile that crosses an adobe wall ofcompacted mud The wall is non-reflective because it is composedof homogenized clay-rich material which has no boundaries thatwould reflect radar energy Its composition also attenuates energyproducing areas of no reflection

about the human past Most archaeological geophysics is stillfocused on its application of finding buried objects or featuresthat can later be excavated using traditional archaeologicalmethods The GPR processing and image production methodsillustrated here are becoming routine and most practitionerscan now produce accurate three-dimensional images of theground If they are correctly interpreted GPR images cannow be used to test hypotheses about human activity suchas social organization and other anthropological questionsFor instance if models of historic human activity can berelated to the placement orientation shape and clustering ofburied architecture then GPR mapping is capable of accuratelytesting these hypotheses or developing new ideas about thepast (Conyers 2010 Conyers and Osburn 2006) In this wayGPR can potentially tell a great deal about archaeological siteswithout ever having to excavate which will be of great benefitin the future as traditional archaeological digging becomesmore expensive and is often curtailed due to preservationissues

Figure 16 Amplitude slice map that shows adobe walls as areas ofno reflection bounded by layers of eroded adobe from the wallsinterbedded by wind blown sand The eroded areas are highlyreflective as these interfaces produce a good deal of radar energyreflection

Conclusions

Ground-penetrating radar has the unique ability of near-surfacegeophysical methods to produce three-dimensional maps andimages of buried architecture and other associated cultural andnatural features for landscape analysis Using high-definitiontwo-dimensional reflection profiles three-dimensional maps

S21

L B Conyers

of amplitude changes can define physical and chemicalchanges in the ground that are related to the cultural materialsof importance When these data and maps are used to test ideasabout human activities of all sorts they offer a powerful andtime-efficient way to study ancient human behaviour socialorganization and other important archaeological concepts

In the processing of GPR reflection data maps and imagesmust be generated and then integrated with information aboutsediments soils and the geometry and composition of buriedcultural features in order to make accurate interpretationsabout what is preserved in the ground This can be done byplacing these cultural data from excavations within horizontalamplitude maps that produce images of only certain amplitudeswithin a three-dimensional volume of radar reflections whichmight be high amplitudes from important buried features butalso could be areas of no reflection at all In some casesonly a detailed analysis of reflection profiles can differentiatenatural geological layers from cultural features especiallywhen the ground contains an abundance of reflections Inall cases the results of GPR reflection images must beidentified and mapped spatially in the ground When multipleimages that are both two and three dimensional in view areinterpreted they can provide a powerful tool for the integrationof archaeological sites within what are often complex groundconditions

References

Annan A P and Davis J L 1992 Design and development of a digitalground penetrating radar system Ground Penetrating Radar

ed J A Pilon (Ottowa Canada Geological Surveyof Canada) Geological Survey of Canada Paper 90-4pp 49ndash55

Conyers L B 2004a Ground-penetrating Radar for Archaeology(Walnut Creek CA Altamira Press)

Conyers L B 2004b Moisture and soil differences as related to thespatial accuracy of amplitude maps at two archaeological testsites Proc 10th Int Conf on Ground Penetrating Radar (DelftThe Netherlands 21 June 2004) pp 67ndash72

Conyers L B 2010 Ground-penetrating radar for anthropologicalresearch Antiquity 84 175ndash84

Conyers L B Ernenwein Eileen G and Leigh-Ann B 2002Ground-penetrating radar discovery at Petra Jordan Antiquity76 339ndash40

Conyers L B and Leckebusch J 2010 Geophysical archaeologyresearch agendas for the future some ground-penetrating radarexamples Archaeol Prospect 17 117ndash23

Conyers L B and Osburn T 2006 GPR Mapping to testanthropological hypotheses a study from comb wash UtahAmerican Southwest Proc 11th Int Conf onGround-penetrating Radar (Columbus OH USA 19ndash22 June2006) pp 245ndash9

Gaffney C and Gater J 2003 Revealing the Buried Past Geophysicsfor Archaeologists (Stroud UK Tempus)

Goodman D 1994 Ground-penetrating radar simulationin engineering and archaeology Geophysics59 224ndash32

Kvamme K L 2003 Geophysical surveys as landscape archaeologyAm Antiquity 63 435ndash57

Leckebusch J and Rychener J 2007 Verification and topographiccorrection of GPR data in three dimensions Near SurfGeophys 5 395ndash403

Leckebusch J Weibel A and Buhler F 2008 Semi-automaticfeature extraction from GPR data Near Surf Geophys6 75ndash84

S22

L B Conyers

of amplitude changes can define physical and chemicalchanges in the ground that are related to the cultural materialsof importance When these data and maps are used to test ideasabout human activities of all sorts they offer a powerful andtime-efficient way to study ancient human behaviour socialorganization and other important archaeological concepts

In the processing of GPR reflection data maps and imagesmust be generated and then integrated with information aboutsediments soils and the geometry and composition of buriedcultural features in order to make accurate interpretationsabout what is preserved in the ground This can be done byplacing these cultural data from excavations within horizontalamplitude maps that produce images of only certain amplitudeswithin a three-dimensional volume of radar reflections whichmight be high amplitudes from important buried features butalso could be areas of no reflection at all In some casesonly a detailed analysis of reflection profiles can differentiatenatural geological layers from cultural features especiallywhen the ground contains an abundance of reflections Inall cases the results of GPR reflection images must beidentified and mapped spatially in the ground When multipleimages that are both two and three dimensional in view areinterpreted they can provide a powerful tool for the integrationof archaeological sites within what are often complex groundconditions

References

Annan A P and Davis J L 1992 Design and development of a digitalground penetrating radar system Ground Penetrating Radar

ed J A Pilon (Ottowa Canada Geological Surveyof Canada) Geological Survey of Canada Paper 90-4pp 49ndash55

Conyers L B 2004a Ground-penetrating Radar for Archaeology(Walnut Creek CA Altamira Press)

Conyers L B 2004b Moisture and soil differences as related to thespatial accuracy of amplitude maps at two archaeological testsites Proc 10th Int Conf on Ground Penetrating Radar (DelftThe Netherlands 21 June 2004) pp 67ndash72

Conyers L B 2010 Ground-penetrating radar for anthropologicalresearch Antiquity 84 175ndash84

Conyers L B Ernenwein Eileen G and Leigh-Ann B 2002Ground-penetrating radar discovery at Petra Jordan Antiquity76 339ndash40

Conyers L B and Leckebusch J 2010 Geophysical archaeologyresearch agendas for the future some ground-penetrating radarexamples Archaeol Prospect 17 117ndash23

Conyers L B and Osburn T 2006 GPR Mapping to testanthropological hypotheses a study from comb wash UtahAmerican Southwest Proc 11th Int Conf onGround-penetrating Radar (Columbus OH USA 19ndash22 June2006) pp 245ndash9

Gaffney C and Gater J 2003 Revealing the Buried Past Geophysicsfor Archaeologists (Stroud UK Tempus)

Goodman D 1994 Ground-penetrating radar simulationin engineering and archaeology Geophysics59 224ndash32

Kvamme K L 2003 Geophysical surveys as landscape archaeologyAm Antiquity 63 435ndash57

Leckebusch J and Rychener J 2007 Verification and topographiccorrection of GPR data in three dimensions Near SurfGeophys 5 395ndash403

Leckebusch J Weibel A and Buhler F 2008 Semi-automaticfeature extraction from GPR data Near Surf Geophys6 75ndash84

S22