Introduction

AERIAL ARCHAEOLOGY AND AIR PHOTO MAPPING IN BRITAIN

Introduction

The published papers of the fourth Ciclo di Lezioni at Siena in January 1991 already contain a general description – from the British viewpoint – of the basic principles and practice of oblique and vertical air photography for archaeological research and conservation (MUSSON, WHIMSTER 1992). Only a few points need further emphasis here, as an introduction to an up-dated de scription of procedures for the mapping and documentation of information from air-photographs in Wales (and, in passing, in other parts of Britain). The merits of vertical air photography for the discovery, recording, mapping and documentation of archaeological sites and landscapes, of all periods, have long been recognised, and this source of information has been extensively exploited in northern Europe, and to a certain extent at least in Italy. The particular value of overlapping, and therefore stereoscopic, images covering the whole of any landscape under study, needs no emphasis, com pared with the more partial record provided by targeted oblique photogra phy. But archaeologists often experience problems in gaining access to the vertical archives, and quickly come to recognise that vertical photography taken for military purposes, for survey or for monitoring has all too rarely been taken in conditions of lighting or crop-development that favour the rendering of archaeological detail. These shortcomings will always limit the power of vertical photography if applied in isolation. The papers given at Siena in the 1999 symposium, moreover, made it abundantly clear that high-resolution satellite imagery, at 1m or better dis crimination and with passes every few days over any part of the globe, will very soon supplement the information available from traditional vertical pho tography, and may in some respects (in time) replace it. In theory, at least, tomorrow’s archaeologist will be able to choose from repeated coverage of any desired target area, and will enjoy a greater chance of identifying im agery which shows cropmarks, soilmarks, earthworks or built remains to best advantage. Progress in this area will surely be rapid in the coming years, not least through the opportunity to experiment with a wide variety of dig ital data, readily capable of manipulation to enhance archaeological detail or context.

©2003 Edizioni all’Insegna del Giglio - vietata la riproduzione e qualsiasi utilizzo a scopo commerciale – 1 That said, experience from Britain and other parts of Europe suggests that relatively traditional oblique air-photography, undertaken preferably by archaeologists and in any case specifically for archaeological purposes, will continue to be a fruitful – indeed essential – component in the effective ex ploitation of the aerial viewpoint for the discovery, recording, interpreta tion, mapping and documentation of the historic environment (see MUSSON 1994). While digital cameras (soon but not quite yet) and increasingly so phisticated in-flight aids (like GPS and digital displays of the known archae ology of the flight area) may enhance the efficiency of the air-borne opera tion – and to some extent the time-consuming post-flight procedures – the advantages of such purpose-made air photography will remain the same. – The photography will from the outset benefit from clear archaeological objectives, whether in primary reconnaissance (the first search over areas of sus pected but as-yet unrealised potential) or in problem-oriented research (such as the definition of road-lines or agricultural patterns round Roman or later settlements). – The objectives will be directly understood by the archaeologist-photographer, through years of archaeological and aerial experience, so that every part of the landscape will be examined, with understanding, for its archaeological potential. – Recording will be done at the time of year, time of day or state of crop development best capable of revealing archaeological information, and the angle of view will be chosen to provide the most striking, most informative or most ‘mappable’ presentation of the evidence available by the camera. – While the information in the photographs will best reach other archaeologists, planners and conservators through mapped and documented transcrip tions, the photographs themselves will still have an intrinsic value. Powerful images – whether of ‘new’ sites or of known monuments, landscapes or townscapes – will (on British experience) figure prominently in the public pres entation of archaeology and hence in raising awareness of the historic environ ment and of the need to protect it from unnecessary damage or destruction. The more ‘remote’ forms of aerial recording (by vertical photography, satellite imagery and the like) will never replace these characteristics of archaeologically-directed low-level air photography, taken by well-informed aerial archaeologists who know the current state of recording and research in their area, who appreciate the kind of information needed for research and conservation, and who have an eye for the striking image (along with the experience to capture it on film). Equally essential, however, will be the capacity to find practical ways of getting into the air (at reasonable cost, within the local context), and of over coming bureaucratic or other restrictions on the practice of aerial photography. While experience elsewhere may provide helpful examples, the lesson from re-

©2003 Edizioni all’Insegna del Giglio - vietata la riproduzione e qualsiasi utilizzo a scopo commerciale – 2 cent experience in central and eastern Europe is that local people must find local solutions, not only to bureaucratic impediments but also to the definition and exploitation of an aerial archaeology adapted to local needs and conditions. There is no single kind of aerial archaeology to which people elsewhere should aspire (such as the rich cropmark archaeology of lowland Britain or, in Italy, of the Tavoliere). Regions without significant cropmark evidence may offer much by way of soilmark recording or earthwork archaeology. The traces of urbanisation or industry will almost always be susceptible to fruitful recording from the air. And everywhere there will be the broader landscape of topography and land-use which provides both the modern and the ancient context for archaeological remains of all periods. The contribution of aerial archaeology will inevitably vary from country to country, and from region to region. But, wherever it is applied, it will only realise its full potential when it mobilises low-level oblique photography along side vertical photography, satellite imagery and other remote-sensing techniques in a mutually supportive co-operation. Further, it will be at its most effective only when it forms part of an integrated approach to the discovery, recording, interpretation, presentation and conservation of the historic environment. In this pursuit individual photographs (to be sure) will still have their uses, but the key element will be the conversion of information from myriads of photo graphs into a smaller number of mapped and documented records, intelligible and accessible to archaeologists and other end-users, whether in research, edu cation, presentation, conservation or rescue and salvage work. If we were asked to name a single main advance in British aerial archae ology in the last decade it would be the progress made in the application of aerial evidence, through structured and progressively-digital mapping and record-creation, and through the routine inclusion of aerial evidence in the daily processes of local and national archaeological services. For air-photog- raphers one of the greatest satisfactions is to see their results used in other people’s research, through mapped and text-based information rather than through the photographs themselves. For example, air-photographic infor mation, mapped and documented by experts in the art, is now regularly used in many parts of Britain to identify the archaeological context of potentially destructive development projects, and hence to support protective measures or to assist salvage work when it becomes unavoidable. In the light of this and other applications British aerial archaeologists can feel some satisfaction that their particular skills and perspective are now finding a proper place in the mainstream practice of archaeological exploration, interpretation, pres entation and conservation. On this note of (not yet fully justified) optimism, we now turn to prac tical examples of air-photo mapping and documentation in Wales and other parts of Britain. C.R.M.

SUMMARY In Wales, air photo mapping by the Royal Commission the Ancient and Historical Monuments of Wales is increasingly playing a part in the record ing of a number of the country’s most important archaeological landscapes. This method of survey has been found to be extremely effective for creating a record both of plough-levelled lowland landscapes but also for preserved upland landscapes, as a preliminary to measured ground survey but also as a method of rapid survey in its own right (see http://rs6000.univie.ac.at/AARG/ worldwide/wales/wales.html). Air photo mapping is now increasingly being linked to the Uplands Initiative programme of field survey, funded by the Royal Commission. Since its inception in 1995 in Wales, this computer-based programme has been developed both through in-house work at the Royal Commission, and through limited regional funding to the Welsh Archaeo logical Trusts. This paper is intended to review the first five years of the programme and present some of the key results achieved for many different archaeological landscapes in Wales.

AIR PHOTO MAPPING IN BRITAIN Air photo mapping is now firmly established as a method of first level rapid survey – and detailed site survey – in many parts of Britain. The leading programme in Britain is the National Mapping Programme (NMP), devel oped by the Royal Commission on the Historical Monuments of England (RCHME), now English Heritage, in the mid-1980s and running as a full programme since 1992 (for a summary, see BEWLEY 1997; good examples of air photo mapping carried out by RCHME can be seen in WHIMSTER 1989). To date some 25% of England has been mapped. Earlier work had focussed on individual site plots or, more commonly, discrete landscape blocks. The NMP has a landscape approach whereby all artificial (man-made) features visible on oblique and vertical air photographs are transcribed onto 1:10,000 scale paper maps. Currently it has the equivalent of 13 staff working in Eng lish Heritage offices or funded positions in local authorities, and has been involved in over 20 projects. In recent years the work has increasingly em braced digital mapping receive technology. A system of air photo mapping in MapInfo GIS, combined with scanned, rectified images from AERIAL 5, has been in place at Northamptonshire Heritage for some years, developed by Phil Markham (MARKHAM 1998) The NMP has been involved in the mapping of some major English landscapes including Salisbury Plain, the Yorkshire Dales, and the Yorkshire Wolds, the latter the subject of a major book by Cathy Stoertz (STOERTZ 1997). In Scotland, the Royal Commission on the Ancient and Historical Monu-

©2003 Edizioni all’Insegna del Giglio - vietata la riproduzione e qualsiasi utilizzo a scopo commerciale – 4 ments of Scotland (RCAHMS) began its programme of mapping cropmarks in 1984, against 1:10,000 scale base maps. Since that time, the process has become entirely digital with plots forming an integral layer of information within the RCAHMS GIS. Unlike the approach in England and Wales, only cropmarks of plough-levelled archaeological sites are mapped and, in some instances, earthworks of ridge-and-furrow cultivation remains where these are difficult to survey on the ground. In all other instances, earthwork sites will be surveyed in the field rather than being mapped from air photographs. Air photo mapping is also carried out by companies specialising in aerial work, usually as a part of the standard planning process. One of the chief expo nents of high quality air photo mapping for a range of archaeological, planning and management uses is Air Photo Services Ltd whose website provides examples of photo interpretation and finished mapping (see www.airphotoservices.co.uk).

DEVELOPING AIR PHOTO MAPPING IN WALES (Fig. 1) Since 1995 a programme of digital air photo mapping and record crea tion in Wales has begun to make a significant impact on the study of upland and plough-levelled lowland archaeological landscapes in the country (DRIVER 1996). The Welsh air photo mapping programme was started some 10 years after the Royal Commission in England began its NMP and to date some 5% of Wales has been mapped. It has a similar remit to rapidly record all redundant features of the built landscape from earliest times until the end of the Second World War, mapping and recording all sites for a 25 sq. km area in about 10 days. As a process of desk-based rapid survey, it is extremely effective in providing a first-level record and map of all visible features in a given landscape, often prior to follow-up programmes of ground survey and field work. The provision of grant-aid to fund air photo mapping in the regional archaeological Trusts, between 1996 and 1998, also allowed these bodies to improve their Sites and Monuments Records and respond more effectively to Development Control work. Crucially, the programme in Wales has always been computer-based and provides a digital plan of each and every site mapped. Since 1995 the work has developed enormously in terms of technology and technique, from the days of FastCAD and FastMAP GIS between 1995 and 1998, to the change over to ArcView GIS in 1999 and the appointment of a new air photo mapping officer.

AIR PHOTO RECTIFICATION IN WALES: SOFTWARE AND ACCURACY Neither photogrammetry nor orthophotography are employed during rectification from oblique and vertical air photographs as this is rapid survey. Digital terrain models are sometimes created within photo-rectification soft-

©2003 Edizioni all’Insegna del Giglio - vietata la riproduzione e qualsiasi utilizzo a scopo commerciale – 5 ware used to aid correction of landscapes with pronounced height distor tions for special mapping projects (eg: Blaenavon). At the same time, the ArcView 3D Analyst extension has been employed to aid the presentation of particular landscape projects. When the mapping programme began in 1995, the Bradford Aerial programme version 4 was used for rectification in the flat plane. Since that time, the work has developed to the point where AutoCAD Map (version 3) is used on a daily basis for photo-rectification to produce a vector plot of the archaeology, while the Bradford Aerial version 5 is used for rectification of complete scanned images where the archaeology is particularly dense or complex. With careful checking of the photo ‘control points’ against which air photo data is matched to the Ordnance Survey basemap, the accuracy levels we require for 1:10,000 first-level mapping are easily achieved. These are to within 5m on level terrain and between 5-15m in undulating or hilly terrain. For archaeological sites in level terrain, surrounded by good map ‘control’ (eg: intersections of mapped field boundaries) errors factors can be reduced to 2 or 3m on the ground. However, the actual accuracy of the base-map being used is an important factor to consider. With 1:10,000 Ordnance Sur vey base-maps only guaranteed accurate to 4-5m in remote terrain, any bet ter figure obtained from photo-rectification software may well be spurious.

PHOTO SOURCES AND THE MAPPING PROCESS The main air photographic source for the mapping programme has not been oblique but vertical air photographs. The Royal Commission holds an extensive archive of historic vertical air photographs, taken by the Royal Air Force and the Ordnance Survey for non-archaeological purposes from around 1945. During the course of air photo mapping this archive of air photogra phy has frequently yielded interesting information. Early prints can show landscapes prior to the effects of afforestation, urban expansion or intensive farming. Particular sorties may show sites and landscapes in exceptional weather or lighting conditions, rarely seen during more recent archaeologi cal aerial reconnaissance. Rectified site data is usually imported into ArcView GIS as a DXF, AutoCAD DWG file or rectified TIF image (from AERIAL 5). These rectified images are classed as raw data, and require subsequent drawing-up in ArcView, with reference to the original photo sources, to produce a finished plot. Data is entered into the ArcView tables providing immediate on-screen informa tion behind every line and polygon. However, full archaeological site records are also created for sites within the Extended National Database (END) for Wales. Incorporated into a GIS, the air photo plots can then be viewed against other datasets, such as the END databases, Upland Initiative field survey areas and vertical and oblique air photo databases.

Cors y Gedol – Prehistoric field systems and mapping accuracy The accurate mapping of archaeological features is essential to ensur ing a reliable record in the immediate term and for forming a basis for man agement in the longer term. Measured ground survey, as opposed to rapid field survey, is the ideal for the creation of an accurate plan, but can be costly and, all too often impractical to fund over large areas of several square kilo metres or entire landscapes. If air photo mapping is to be considered a use able and reliable method for creating a first-level but permanent record of archaeological sites, both in upland and lowland locations, questions of positional accuracy and accuracy of interpretation must be satisfied. With this in mind, the Royal Commission included the field system at Cors y Gedol, a Scheduled Ancient Monument, in its early programme of trial air photo mapping in Ardudwy at a time when ground survey of this site was already in progress (See CREW, MUSSON 1996, 24-25). Figure 2 shows the interesting field patterns at Cors y Gedol. The ir regular western fields are slightly terraced showing use of the plough, and crowded with clearance cairns. Within the irregular fields are isolated pre historic huts, groups of Romano British huts and medieval structures. The field pattern opens to the east in a more regular, rectilinear pattern with an associated track way. The fields at Cors y Gedol were mapped from vertical and oblique air photographs using standard procedures for rectification and finished draw ing adopted for all first-level mapping in Wales. The gently sloping nature of the ground and generally even terrain obviated the need for the construction of a Digital Terrain Model and instead, with rectification instead carried out in 2 dimensions. At the same time as our mapping work, the field system was also the subject of a full ground survey allowing our rapid-survey efforts to be contrasted with more detailed work. In the detailed plot, Figure 3, showing the AP work in red and the ground survey in black, we can see that the results of comparison are encour aging. The ground survey contains a high amount of detail. However, the detail identified and mapped from air photographs, shown in red, matches the ground survey very well. There is a consistent shift of about 3.8m across the survey area between the air photo and ground survey, due to the sloping ground across the site. In the centre of the area, the maximum disparity between the plot of the main oval enclosure and the ground survey is 5.3m. However, the air photo map adds a house platform within the enclosure, a faint feature visible on air photographs but less obvious on the ground. For the most part, these errors are well within the tolerances of the Ordnance Survey basemap in this 1:10,000 mountain and moorland area.

©2003 Edizioni all’Insegna del Giglio - vietata la riproduzione e qualsiasi utilizzo a scopo commerciale – 7 We must consider that, if for a variety of reasons, ground survey was not possible for a given area, and an air photo map such as this was the only comprehensive plan on which to base research and management conclusions, then it would be an effective tool. Indeed, an air photo map remains the only accurate plan for many of the field systems in Ardudwy until measured ground survey is more widely implemented.

Mynydd Epynt – Peopling a forgotten landscape Without doubt, air photo mapping is most effective when applied to an entire landscape or to a consolidated block of land. In 1996 the decision was made to embark on the mapping of Mynydd Epynt, a major upland landmass in mid-Wales, owned and managed by the Ministry of Defence (MoD) as the Sennybridge Army Field Training Centre (DRIVER 1997). The Epynt had long been regarded as a potentially rich archaeological landscape. Its evacuation and requisitioning by the military in 1939 for use as a training area (BRIGGS 1994) had helped to preserve it as a relict agricultural landscape relatively untouched by the advance of modern settlement and agricultural ‘improve ment.’ The project area measures some 236.25 sq. km, which included the central landmass of Mynydd Epynt, an exposed tract of upland moorland drained by a series of more fertile valleys. The existing record listed a number of well-known Scheduled Ancient Monuments, among them two prehistoric enclosures, several Bronze Age cairns and a stone circle. Remaining records were largely restricted to upstanding historic buildings and some better-known abandoned farmsteads. What we lacked was a detailed and comprehensive survey of the entire landscape to allow us to assess the exact nature of the surviving archaeology and to place known monuments in a clearer landscape context. Vertical air photographs were virtually the sole source used for the mapping work. Although photographed from a height of 20,000ft, low No vember light combined with the high quality of image allowed the identifica tion of even small earthwork features under a metre across, when the prints were magnified and viewed in stereo. The project results exceeded initial expectations; more than 670 ar chaeological sites were mapped from 256 sq km of land, of which 472 were new to the record, representing around a 238% increase in known sites. The project was an exercise in rapid survey with mapping and recording taking 16.7 weeks to complete. The greatest gains lay in the medieval and post- medieval periods, although sites belonging to prehistoric or unknown peri ods were also recorded. The picture of rural settlement across the area was significantly enhanced by the discovery of previously unrecorded farmsteads, long houses, field systems, stock enclosures and traces of rural industry. Aerial discoveries included many substantial field monuments. At Blaen Duhonw, a pair of well-preserved long houses was recorded along with two attendant ‘pillow mounds’, artificial rabbit warrens built to supplement the

©2003 Edizioni all’Insegna del Giglio - vietata la riproduzione e qualsiasi utilizzo a scopo commerciale – 8 income and food supply of those living in this secluded valley. The precise date of the houses is uncertain, as this type of structure pervades in the Welsh uplands from Medieval times onwards. None of these substantial structures was recorded on early or modern maps and they would thus have remained ‘invisible’ during any desk-based survey which did not include aerial photo graphic sources. Mynydd Epynt – Seeing through the forestry The Mynydd Epynt project offered the opportunity to assess the role of historic mapping against vertical air photographs for identifying archaeo logical sites, particularly the historic Ordnance Survey County Series pro duced between 1890 and 1905. This type of map is commonly used to locate archaeological sites in areas which have not been previously studied, includ ing areas planted out for commercial forestry in post-war years. The planta tion of Crychan Forest on the Epynt was completely mapped from 1945-6 air photographs taken prior to afforestation or during initial forestry plough ing. Following this, map sources were examined. Of 45 ‘new’ sites discov ered, including 13 farmsteads and 24 enclosures, only 5 were shown on early maps and in some cases key landscape features (trackways, holloways, field boundaries) had been omitted. The locations of even extensive farmsteads, and notable site complexes elsewhere on the Range (eg: The Warren), were often shown as featureless upland moor. The question of the visibility of archaeological sites in the modern day was also raised during field visits to locate AP sites in 1997. Of those in for estry, some were inaccessible in mature conifer plantations, or, if accessible, plough-damaged and obscured by planting. Similarly, in open ground, it was noted that reduced post-war upland grazing had allowed renewed bracken growth, rendering a number of earthwork sites invisible or obscured to field surveyors in the present day. In these instances, historic vertical air photographs often stand as the sole photographic records of particular archaeological sites. Mynydd Epynt – Using the mapping for site management In management terms, the timing of the Mynydd Epynt project was fortuitous. In recent years, the Ministry of Defence (MoD), as landowners, have fostered a growing interest in conservation matters relating to their military training areas. In 1997, the MoD initiated an Integrated Land Man agement Plan for the Sennybridge range, a programme of data-gathering and survey to assess all resources which require management or protection. The archaeological report published from the Mynydd Epynt project (DRIVER 1997(i)), which included a detailed gazetteer of all sites mapped, provided the MoD with a first-level index for their archaeological resource. Coupled with this, a further report listing 29 sites requiring protection against ‘digging and disturbance’ was prepared for the military. This has already been used by range

©2003 Edizioni all’Insegna del Giglio - vietata la riproduzione e qualsiasi utilizzo a scopo commerciale – 9 staff in planning, or re-routing, training activities in the vicinity of archaeo logical sites. In the longer term, the results of the Mynydd Epynt project have fed into an ongoing programme of ground survey, funded by Cadw, to investi gate Deserted Rural Settlement sites in the county of Powys. This project may in turn lead to recommendations for the protection of the better pre served sites as Scheduled Ancient Monuments. Consequently, the air photo map and database is now acting as its own research tool, assisting in the planning of detailed field investigation. It is also acting as an important man agement tool with the provision of a digital plan and a full text record for every site mapped, using a standard level of accuracy and set of conventions.

Llyn Hiraethlyn – From air photo map to published national mapping. It is worth examining one particular output from the mapping pro gramme in Wales in some detail. In addition to providing archaeological in formation for research and management purposes, the Royal Commission in Wales also has a responsibility to provide site plans, or ‘Antiquity Models’, to the Ordnance Survey for inclusion on their basic scale mapping. These have been traditionally provided from measured ground survey, but as the amount of air photo mapping in Wales increases, so we are able to provide informa tion in digital form direct from this new source. We will turn now to follow one particular site from its initial aerial discovery to its final publication, and look at the main steps of this process. In late Spring 1996, during RCAHMW aerial reconnaissance in Snowdonia, in hills to the south-east of the major Roman complex of Tomen y Mur near Trawsfynydd (CREW, MUSSON 1996, 26-28), two characteristic square earth works were spotted on a flat ridge above a lake called Llyn Hiraethlyn, in fact two unrecorded Roman practice camps (ibid, 30; see Tav. XI, b). On returning to the office, good-quality vertical air photographs were examined for the same area. When viewed in stereo, not two but three camps were visible but their positions did not correspond with the pair recently photo graphed. When both oblique and vertical sources were combined and inter preted, and a digital air photo map made, it was seen that the group in fact comprised three larger practice camps and a fourth smaller camp. It is inter esting to note that neither air photo source clearly showed all four camps, even with the benefit of hindsight. The resultant air photo map was duly given to our survey staff to use in the field to check the accuracy of the plot as it was proposed that it should form an Antiquity Model for Ordnance Survey map inclusion. The results of the field check confirmed the plots accuracy within 4-5m. One of the first outputs for this data was its inclusion in the journal of Roman archaeology, Britannia, for 1997 (DRIVER et al. 1997) to illustrate the discovery. The pro vision of a plan direct from the raw air photo plot shows the flexibility of the

©2003 Edizioni all’Insegna del Giglio - vietata la riproduzione e qualsiasi utilizzo a scopo commerciale – 10 digital technique, whereby with a little editing and consideration for layout, plans can be output at a variety of scales and in a variety of forms with the minimum of effort. The real achievement from the Llyn Hiraethlyn example was the ap pearance of the final Antiquity Model on the new 1999 OS Landranger tour ist map for the area. The process by which a previously unrecorded earth work was photographed in 1996, and via air photo mapping has been pub lished on the map in 1999, represents a significant step both in terms of outputs from the air photo mapping programme, and in the provision of data to the Ordnance Survey. In future, it is hoped that this process can be repeated beyond the dozen or so current test examples, and refined. A view of the future: The Blaenavon Landscape Project This paper has examined many elements of aerial work in Wales, but these are now being combined in an ongoing current project which is contrib uting to a prestigious end. Since 1998, the Royal Commission has been work ing in support of the World Heritage Site Nomination for the Blaenavon In dustrial landscape in South East Wales. The initiative for including Blaenavon on UNESCO’s world heritage list has been taken forward by Torfaen County Borough Council (within whose boundary Blaenavon town and most of the landscape lies), supported by the Royal Commission and Cadw, and by a number of other bodies (for details visit: http://www.world-heritage-blaenavon.org.uk/). Blaenavon is a remarkable for many reasons. The area around Blaenavon is one of the finest examples of a landscape created by coal mining and ironmaking in the late 18th and early 19th centuries. Many early industrial features survive in the landscape, including the core site of Blaenavon iron works (shown here on the nomination document), dating from 1789, and the most complete ironworks of its type and period remaining in the world. Aerial reconnaissance for the World Heritage Nomination During 1998 and 1999 the Welsh Royal Commission carried out two long flights over Blaenavon in support of the World Heritage Site nomina tion. New archaeological aerial photography was needed for our own aerial archive, while photographs of specific views were required to illustrate the Nomination Document. However, the Royal Commission has been over fly ing Blaenavon since the early 1990s for the purposes of aerial monitoring of scheduled monuments and for industrial recording. These monitoring photographs, which document the condition of pro tected monuments on a 3-4 yearly basis, quickly become important historical records in their own right. In the context of Blaenavon, they have also dem onstrated a commitment to regular site monitoring, from the air, for the purposes of the World Heritage Nomination.

©2003 Edizioni all’Insegna del Giglio - vietata la riproduzione e qualsiasi utilizzo a scopo commerciale – 11 The targeted aerial reconnaissance, in support of the World Heritage Nomination, was really geared towards obtaining aerial views which would set the key monuments in their landscape context, particularly wide-angle views drawing in a great amount of detail. The air photographs have been used in the Nomination Document, often alongside interpretative diagrams explaining the position of features within the frame. However, in terms of the archaeological data shown on them they are only the raw data for the process of subsequent interpretation and mapping.

AIR PHOTO MAPPING Air photo mapping has also been carried out for the entire landscape by David Thomas of RCAHMW (THOMAS 2000). Figure 4 shows an example of mapping for one of the most complex landscape areas – Hill Pits, where a main tramroad connects a series of small coal pits in the midst of a very complex system of water channels, inclines and tramways. The great value of having this archaeologically accurate mapping on screen in the GIS is that historic cartography, including early maps, tithe maps and manuscript maps from mine surveys, can be draped over the aerial data to provide additional information. With the very public focus of this site nomination, and the forthcoming initiative for greater publicity and interpretation on site, the ArcView 3D Analyst extension was used to produce 3D visualisations of the landscape, generated from Ordnance Survey Land-Form data. New life was breathed into 1940s RAF vertical air photographs when these were draped over the 3D models as image files, giving an historic dimension to the virtual land scapes. As well as being visually stunning, this 3D work had a serious side. Without taking to the air in a light aircraft it is impossible for most members of the public to see the varied landscape of Blaenavon from an elevated per spective. With the industrial features in mind, the virtual landscape also al lows people to visualise how systems of water supply and transport worked, particularly where topography and gravity were employed. The final stage in this combined approach to survey has been the fund ing of ground-based survey within the RCAHMW Upland’s Initiative, work still in progress. Data from the air photo mapping can be made available digitally to fieldworkers and used in the field as a valuable tool to aid site recognition and recording within complex archaeological landscapes. Infor mation noted in the field is, in turn, fed back to RCAHMW to enhance the air photo mapping work and site database. Such a process is being developed at RCAHMW to allow close cooperation in future between the results of the air photo mapping programme and the ongoing work of the Uplands Initia tive.

In conclusion, the aim of this paper has been to illustrate some of the ways in which two established methods of survey, aerial photography and air photo mapping, can continue to inform us about the nature of past human settlement in both lowland and upland landscapes. The first part of this paper has shown the various ways in which con tinuing aerial reconnaissance, combined with vertical and satellite imagery, can be used to discover new sites, and to monitor known ones. Used as a research tool, aerial photography can clarify complex patterns of archaeo logical features which may be difficult to comprehend at ground level, and record entirely new evidence which may remain too ephemeral to be se curely identified during field survey. The second part of this paper has shown the impact which air photo mapping can have at 1:10,000 scale and greater, for recording all types of archaeological remains. While air photo mapping has traditionally been used to map cropmarks or soilmarks in intensively farmed lowland landscapes, the technique has proved particularly effective for mapping upland land scapes in Wales where previously unrecorded earthwork monuments still await re-discovery and basic survey. The simple, cost-effective, digital approach allows resulting site plots and records to be readily combined with other datasets, and output for field plans, project reports and publications, so as sisting future programmes of ground-based survey and better management of the cultural heritage of Wales. Air photo mapping will never accurately depict every detail or identify every site in a landscape. Small area features such as burnt mounds, cairns or house platforms, will remain difficult to correctly identify from a high level. However, as it is being used in Wales, as a preliminary to ground survey within the Uplands Initiative, it can be an extremely effective method and this integration of air photo and ground work should be continued and ex tended in the future. T.D.

TOBY DRIVER, CHRIS MUSSON

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