use of remote sensing data for archaeological landscapes

8/9/2019 Use of Remote Sensing Data for Archaeological Landscapes

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1 INTRODUCTION

The practice of using remote sensing techniques for visualising archaeological sites and

landscapes has traditionally been based on lo altitude aerial photography using film

sensitive at optical and sometimes near infrared avelengths! In the 1"#$s O!%!&!

Craford' the archaeological officer of the (ritish Ordnance %urvey' demonstrated that

archaeological structures could be delineated from shado' soil and crop mar)ings on

panchromatic aerial photography *Craford 1"#+' 1"#,' 1"#"' Craford and -eiller

1"#,.! %ince that time' both oblique and vertical aerial photography have been used e/0

tensively for archaeological reconnaissance and mapping all over the orld! mong the

very first practitioners of aerial archaeology ere Craford and llen' ho undertoo)e/tensive surveys in (ritain and the 2iddle 3ast' and the 4renchman ntoine 5oidebard

ho surveyed a large part of %yria! These pioneers helped to refine the instruments and

establish methods that are still in use today! Craford in particular established methods

of site classification and rote about the effects of eather' season' soil moisture and

crop type on photographic return *Craford 1"#+' 1"#,' 1"#".! 5oidebard undertoo)

e/periments to evaluate the influence of photographic scale' illumination effects and in0

frared film as he surveyed hundreds of miles of %yrian desert landscape *5oidebard

1"#"' 1"+6.! Today' aerial photography is accepted as a cost0effective' non0invasive

technique for the reconnaissance and survey of monuments! Interpretation is guided by

classification schemes that distinguish beteen description and interpretation of ob0

served features *3dis et al ! 1",".! 7oever' remote sensing should not be seen 8ust as

The use of remote sensing data for visualising and interpretingarchaeological landscapes

D! Donoghue' ! (ec)' N! &aliatsatos 9 -! 2c2anus

Department of Geography, University of Durham, Durham, UK

&! 5hilip Department of Archaeology, University of Durham, Durham, UK

(%TRCT: Remote sensing is a ell established technique that has been employed in

archaeological research for nearly a century! Until recently the technique as limited tosite specific aerial photography focused solely in the visual and near infra0red compon0

ents of the electromagnetic spectrum! Improvements in sensor technology mean that ar0

chaeologists can e/ploit remotely sensed imagery from different electromagnetic

avelengths and platforms! This has the potential to increase the area of study and e/0

tend the indo of opportunity hen archaeological residues can be detected! This pa0

per e/amines the fitness for purpose of modern remote sensing techniques for archae0

ological research from both aerial and satellite platforms! 3/amples are cited from

3uropean and 2iddle 3astern conte/ts!


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an image for visual interpretation! dvances in sensor technology have led' over the

past fe decades' to a range of ground' airborne and spaceborne imaging instruments

that can be applied to archaeological and heritage management problems! ssociated

advances in spatial and visualisation softare' particularly &eographical Information

%ystems *&I%. and image processing systems' allo the sophisticated manipulation of

remotely sensed imagery hich can improve its interpretation! %ignificantly' these ad0vances' coupled ith global positioning technologies' mean that the ma8ority of modern

imagery comes pre0rectified! This paper uses e/amples of landscape reconstruction

here remote sensing imagery has provided valuable information hich ould have

been difficult to obtain by other means!

# IR(ORN3 R32OT3 %3N%IN&

rchaeological structures such as buildings' alls and ditches can usually be seen on

conventional air photography at an appropriate scale and vieing angle! On the other

hand' crop and soil mar)s are more difficult to detect ith certainty! The visibility ofcrop mar)s often depends on vegetation type' soil conditions' sun0sensor geometry and

film sensitivity and so it is e/tremely difficult to obtain photographs under optimal con0

ditions! 2ultispectral sensors address some of these problems because they are able to

loo) simultaneously at a ide range of different avelengths' many of hich are more

sensitive to vegetation and soil status than either the human eye or photographic film!

The limited spectral range of photographic film *+;$ 0 11$$ nm. is overcome by the use

of photoelectric sensing devices here image data is recorded in a digital form! These

devices are able to separate electromagnetic radiation into a number of discrete narro

avebands' hence the term multispectral ! Narro band spectral imaging can often help

to enhance or distinguish different features on the ground according to their particular

absorption and reflectance properties! 2ultispectral scanners *2%%. ma)e it possible tostudy avelength bands that are particularly sensitive to vegetation groth' soil vari0

ations' moisture and temperature! nother ma8or advantage of multispectral imaging is

that the data is produced in a digital form that can be modified using computer0based

image processing techniques! The effect of image enhancement is to allo the user to

e/periment ith different ays of ad8usting the contrast' in an interactive ay' in differ0

ent parts of the image to assist interpretation!

In former etland environments such as the 4enlands of eastern 3ngland and the


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and ground based surveys' see figure 1! 2orton 4en is a reclaimed etland environment

here land drainage and deep ploughing are causing rapid destruction of the archaeolo0

gical record! 2%% data may provide a rapid and cost0effective tool for monitoring

change in such environments!

4igure 1! Daedalus 2ultispectral imagery from 2orton 4en' U- shoing crop mar)s in multispectral im0age data e/tending across the landscape through different crop types *Copyright N3RC.!

more recently study in the


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square barros on a gravel ridge is lin)ed to the dry land by a ditched trac)ay' see fig0

ure #!

Note: image will be supplied later. ormatting has been set accordingly

4igure #! eicester0

shire here an e/periment is being conducted to quantify the value of TI data!


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4igure +! Day and night time thermal imagery from (osorth (attlefield' >eicestershire shoing formerfield boundaries and possible ditch structures in the vicinity of the heritage centre *Copyright N3RC ir0 borne Remote %ensing 4acility.!

+ %T3>>IT3 I2&3R@

Optical space photography dates bac) to the first manned space flights! 7oever' regu0

lar coverage of the 3arth is obtained from sensors on orbiting satellites that use conven0

tional film or digital imaging devices! Until very recently' the optical satellite imagery

available to the public has been of lo spatial resolution and of limited use for archae0

ological prospection and interpretation *llan and Richards 1",+.! lthough' there have

been several studies that have demonstrated the capability of satellite imagery to derive

important environmental information that is of considerable value in archaeological

landscape assessment *for e/ample Co/ 1""#.! 7oever' the last decade has seen to

significant changes: the declassification of military satellite photography and the com0

mercial availability of high resolution satellite imagery!merican Corona and Russian -


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nadir thus offering stereoscopic data! 5resumably due to the cost of their imagery these

sensors have not received as much archaeological attention *although see Campana and

4rancovich #$$+ 4oler #$$1.!

The %ettlement and landscape development in the 7oms Region' %yria *%7R. pro8ect

based around has been evaluating the Corona and I)onos satellite sensors since 1"""

*Donoghue et al. #$$$ 5hilip et al. #$$#a 5hilip et al. #$$#b (ec) et al. #$$+ (ec)et al. in press 5hilip et al. in press.! The satellite imagery is an important component of

this archaeological survey pro8ect! It has framed the ay the landscape has been inter0

preted and has been used to direct the ground survey! 7ence' in a fe seasons field0

or) the pro8ect team has garnered an understanding of the archaeological repertoire

and its broad scale settlement dynamic that ould have ta)en many more seasons of

study if no remote sensing had been employed!

The Corona imagery is the earliest imagery and has recorded an effectively intact land0

scape ith minimal destruction' disturbance or mas)ing of archaeological residues by

modern agricultural or settlement e/pansion! 7oever' this photographic archive is not

georeferenced and there is obviously no fle/ibility in determining hen the photo0

graphy as collected! The I)onos imagery can be collected on demand ithin a collec0tion indo commonly covering 1$ days! This imagery comes in a geo0referenced

format and is therefore ready to use in a digital environment!

This pro8ect encompasses to discontiguous application areas that totals over ?;$

square )ilometres! The study area broadly consists of to different types of environ0

mental Fone: basalt and marl! The archaeological residues in each Fone are mar)edly

different and have been sub8ect to different formation and deformation processes! The

panchromatic and multispectral data ere enhanced using standard image processing

routines such as contrast stretching' density slicing' colour composite production' be0

spo)e contrast enhancement and pan sharpening techniques! The I)onos imagery has a

dynamic range of 11bits and ithout image processing techniques much of the import0

ant information in the structure of the data ould not have been recognised!

rchaeological residues in the basalt Fone are recognised as a palimpsest of field

boundaries' structures and cairns ith structures ranging in siFe from $!;m to ,m! The

spatial resolution of the sensor is the most important aspect in this Fone! The Corona

imagery at #m is high enough for mapping purposes' hoever' the I)onos panchromatic

imagery' at 1m' produces a more readily interpretable product' see figure 6! 4inally' and

most importantly' the Corona imagery requires e/tensive geo0referencing! 3ven ithout

the I)onos imagery as a geo0referencing base the Corona imagery ould still have high0

lighted many residues but locating them on the ground ould have been very difficult!

(y contrast' residues in the marl Fone are recognised as lighter areas in comparison to

the bac)ground soil colour! The ma8ority of the archaeological residues are tells and ploughed out settlements ith a minimum diameter of appro/imately #$m! The in0

creased dimension of residues in the marl Fone increases the range of imagery hich is

effective for prospection! The spectral resolution of the sensor is more important for in0

terpretation in this Fone' see figure ;! The I)onos multispectral allos the creation of

colour composites that improve visual detection! 7oever' modern modifications *i!e!

infrastructure building' settlement e/pansion and deeper ploughing. have increased im0

age comple/ity in the I)onos imagery!


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4igure 6! Comparison of the resolving characteristics of the Corona and I)onos imagery in the basaltFone!

4igure ;! Comparison of the resolving characteristics of the Corona and I)onos imagery in the marl Fone!%ite numbers are labelled in the Corona imagery!


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7oever' due to recent landscape modification the I)onos imagery may not articulate as

much of the archaeological resource as the Corona! Ghen the I)onos and Corona im0

agery are used in con8unction ith one another further benefits are realised as one data

source can be used to validate the other! 4rom a CR2 perspective the analysis of both

data sources provides an overvie of the archaeological residues and the range of de0

structive modifications over the past thirty years! The I)onos imagery provides a mod0ern day snapshot of a landscape under destruction and can therefore be used to determ0

ine the level of threat to the landscape! The introduction of heavy earth moving equip0

ment' particularly the bulldoFer and the mechanical plough' has had a significant impact

on the landscape' see figure ?! This is also demonstrated in figure ; here building and

deep ploughing have altered the structure of the landscape! The I)onos imagery displays

a range of responses that one might interpret as archaeological: in fact they are artefacts

of anthropogenic practices over the last thirty years!

4igure ?! n e/ample of the affects of bulldoFing in the basalt Fone!

6 I%%U3% O4 2U>TI0%3N%OR R32OT3 %3N%IN&

Remote sensing is increasingly important to many areas of archaeological enquiry from

prospection through to management! It is therefore essential that it is not applied inap0

propriately! The e/amples used in this paper have covered a number of differentsensors' in different geographical locales and under different environmental conditions!

3ach sensor has demonstrated its on particular benefit! 7oever' the inappropriate ap0

plication of a single sensor could produce minimal results or the dogmatic application of

that sensor ill have diminishing archaeological returns! The combination of different

sensors ith different characteristics can produce profound interpretative synergies!

2ultiple sensors should be evaluated on the basis of Bfitness for purpose! 4itness for

purpose in this conte/t refers to the costHbenefit returns of each sensor and ould be

based upon an understanding of the nature of the archaeological residues' the sensor

characteristics and the environmental characteristics of the landscape!

The nature of the archaeological residues and their relations ith the immediate matri/

determine ho easily the archaeological remains can be identified! 4or e/ample' it is re0


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latively easy to identify a grave feature hich has been cut into chal) and the bac)0

filled ith soil hereas it can be much more difficult to identify a grave feature hich

has been cut into soil and immediately bac)filled ith the same soil! It is this very con0

trast beteen an archaeological feature and its surrounding matri/ that one is hoping to

identify ith a remote sensing sensor!

The sensor characteristics are determined by the spatial' spectral' radiometric and tem0 poral a/es of resolution! Different combinations of sensor characteristics can be used to

identify different archaeological contrasts! In the e/ample of the grave cut into soil and

bac)filled ith the same soil the application of visual remote sensing on bare soil may

prove to be unproductive! 7oever' magnetometry or 2%% over crop' at the appropriate

period of groth' could identify the contrast more easily!

The environmental characteristics are determined by a range of comple/ natural and

cultural variables that can change over time' sometimes quite rapidly! Cultural actions

such as bulldoFing or ploughing can disrupt or destroy any contrast beteen the archae0

ological residues and their local matri/! >ong term natural actions' such as soil forma0

tion' can also lead to a loss of archaeological contrast! 2uch more difficult to ascertain

are the periodic or seasonal contrast variations that can occur through such mechanismsas changes in soil moisture or crop vigour! 4or e/ample' in the marl environment of

%yria' discussed above' the archaeological residues are identified through differential

soil colour! This soil colour difference is due to variations in soil structure associated

ith the residues! The different soil structures have different ater retention properties

hich result in different reflectance characterics! The contrast in soil colour is increased

at periods of pea) aridity and loered' or even negated' after periods of heavy rainfall!

The temporal aspects of the imagery can be particularly important for archaeological in0

terpretation! number of the most archaeologically threatening issues are related to

modern land management and development practices! Githin this conte/t archived aeri0

al or satellite photography provides a unique tool to model past landscapes prior to de0

structive modification' see figure ?!

2ulti0sensor approaches should provide the greatest costHbenefit return for any area of

archaeological enquiry! 7oever' in order to capitalise on these benefits the ne sensor

technologies need to be evaluated for the effects of eather' season' soil moisture' crop

type and illumination! This ill reinvigorate the theoretical foundations of aerial photo0

graphy developed by Craford and 5oidebard and move the discipline firmly into the

#1st century! This ill be particularly beneficial for the trans0national approaches to her0

itage management in the e/panding 3uropean Union and to those areas of the orld

here the archaeological resource is poorly understood or not inventoried!

; CONC>U%ION%

Remote sensing can provide an impressive picture of the archaeological landscape

ithout the need for invasive or e/pensive survey methods! On the other hand' it can be

used inappropriately' it can be rongly interpreted and it is not necessarily a substitute

for ground0based investigation! The true potential of multispectral remote sensing' in0

cluding thermal imaging' is still not clear and it needs to be evaluated to test responsive0

ness under a broad range of climatic and ground conditions! 4urther research is li)ely to

produce sensors capable of resolving small features such as post0holes and shallo pits!

dvances in thermal imaging ill hopefully help to distinguish sub0surface features as0

sociated ith shallo ground disturbance such as graves' hich are particularly difficult

to detect! Ghen used appropriately' remote sensing provides a basis for testing hypo0


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theses of landscape evolution that may be tested by ground survey' geophysical survey

or e/cavation! >arge0scale airborne and satellite surveys can provide the frameor) on

hich planning policy and e/cavation strategies can be established!

R343R3NC3%llan' A! ! and Richards T! %! 1",+! Use of %atellite Imagery in rchaeological %urveys! !ibyan "tudies 14: 60,!(ec) ! R!' 5hilip &!' Donoghue D! N! 2! and &aliatsatos N! *#$$+.! The archaeological evaluatio of integrated high and medium

scale satellite imagery in %yria! GC' Gashington!(ec) ! R!' 5hilip &!' Donoghue D! N! 2! and &alliatsatos N! *in press.! &eo0locating declassified CORON satellite photography

for archaeological surveys and cultural resource management applications: an interim paper! Gor)shop on erial rchaeologyand Remote %ensing' %iena!

(ellerby TA' Noel 2 and (ranigan - 1""$! thermal method for archaeological prospection: preliminary investigations! Archaeo#metry 32:1"10#$+!

(eley R7' Donoghue DN2' &affney es revelations archaeologiques de la photographie aerienne 0 une nouvelle methode de recherches et dobserva0

tion en region de steppe !1/llustration #; 2ay: ??$0#!5oidebard 1"+6! >a trace de Rome dans le desert de %yrie! >e limes de Tra8an a la conquete arabe! Recherche aeriennes *1"#;0

1"+#.! 5aul &euthner: 5aris!5olesland D and Donoghue D 1""+! multi0sensor approach to mapping the prehistoric landscape! In $roceedings of the 2th

N)%+ Airborne "ymposium! N3RC: %indon' ,,0"?!5olesland D' >yall A and Donoghue DN2 1""=! 3nhancing the record through remote sensing! The application and integration of

multi0sensor' non0invasive remote sensing techniques for the enhancement of the %ites and 2onuments Record! 7eslerton 5arish5ro8ect' N! @or)shire' 3ngland. /nternet Archaeology 2 *http:HHintarch!ac!u)H8ournalHissue#Hpldtoc!html.

%collar I' Tabbagh ' 7esse and 7erFog I 1""$! Archaeological $rospecting and %emote "ensing ! Cambridge University 5ress:Cambridge!

%hennan I and Donoghue DN2 1""#! Remote sensing in archaeological research! In 5ollard 2 *ed. New Developments in Ar#chaeological "cience. O/ford University 5ress: O/ford' ##+0+#!

Tabbagh 1"=?! >es proprietes thermiques des sols! Archaeo#$hysica 6:1#,06,!

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use of remote sensing data for archaeological landscapes

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