Aerial Archaeology in Ireland - The Heritage Council

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to suit their purposes. Most examples contain both distribution maps and/or interpretive plots, as well as reproductions of the photographs themselves, at least on a selective basis. An area that has received less attention (at least until recently) is the consideration and analysis of the whole historic environment — and the history of landscape change — rather than just picking out relict features. For example, in a report for Teagasc, Kavanagh (2002) reviewed the effectiveness of the REPS scheme in relation to the survival and discovery of individual monuments and more general landscape ‘quality,’ but not the wider historic character of the landscape. Where the wider historic landscape character has been addressed effectively, it is often the richness of the photographs themselves that most clearly illustrates the detailed complexity of the rural historic environment and the insidiousness of pressure of change (e.g. Barrett 1997b; 1997/8; Dunford 2002, 2003). Archiving The practice of duplicating sets of aerial photographic material (e.g. NMS copies of photos from CUCAP, OSi, Air Corps, GSI and other sources; National Museum set of CUCAP photos and some other sources) means that much relevant photography is not reliant on its survival for a single source — at least in terms of prints. Moreover, public archives with original material have good storage conditions on the whole. More problems arise with valuable private collections which are available for consultation but not yet fully assessed for their content. There would clearly be merit in duplicate sets of prints being available (subject to copyright restrictions and rights), both for the security of the information they contain and for easier consultation. The growing use of digital imagery and remote sensing techniques poses particular challenges for long-term archiving. The Archaeology Data Service in Britain has published a guide to good practice (Bewley et al. 1998). 23 5.2 Cost-effectiveness, Resources and Co-ordination In very general terms, the cost-effectiveness of aerial archaeology is widely recognised (e.g. Wilson 2001; British Academy 2002). It is not easy to estimate the totality of aerial archaeology carried out in Ireland — not least because a considerable amount of reviewing and plotting of existing photography is done on a case-by-case basis. In any case, this is not the best measure of whether it is used effectively. Johnson (1998) has noted the value of analysing existing photographic archives, observing: ‘Kelleher (1995) reported a high success rate in identifying previously unrecorded sites through the use of computer enhancement and mapping programmes to analyse aerial photographs. The results were particularly impressive in identifying field systems and associated enclosures in marginal areas.’ In terms of reconnaissance for oblique photography, the cost-effectiveness of the technique can be gauged on the basis of ‘yield’ of results per flying time or the approximate cost per new discovery. In the exceptional year of 1989, Barrett (1995b) recorded 137 sites in six hours’ flying along the Barrow Valley between Monasterevin and Bagnelstown. Power (1993) records that over 200 previously unrecorded sites were discovered in just six hours’ flying in the area between Fermoy and Mallow along the Blackwater Valley (c. 20 miles x 5 miles). However, Power also notes that this was highly exceptional. Otherwise, over ten years, the Cork Archaeological Survey undertook 40 hours’ flying, recording previously unknown sites at around one or two per hour. Power observed that ‘…this discovery rate compares very unfavourably with the returns from actual fieldwork — especially in the less intensively farmed parts of the county. The return is even less productive when one considers that those sites not revealed by cropmarks still have to be visited on the ground…’ 23 http://ads.ahds.ac.uk/project/goodguides/adandrs/ 103
104 Estimates of costs per site or target are also variable. These can be expected to vary considerably, depending on how much previous work has been done, weather conditions etc. In the drought year of 1989, with a grant of Stg£2,000, Dr Gillian Barrett recorded 106 new sites (Barrett 1995; pers comm.), giving a figure of c. Stg£19 (€29) per site. Markus Casey (pers. comm.) suggests a rough estimate of c. €50 per new site for his recent work on coastal promontory forts. These figures do not allow for repeat photography/monitoring of known sites within the same sortie. Unfortunately, Doody (2001) does not give figures for the costs of the Bruff survey where comparative medium and low-altitude vertical and oblique reconnaissance was compared with high-level vertical coverage. Estimates for the UK for aircraft costs per ‘target’ (i.e. for both new and known sites) was c. Stg£20 (€31) in 1996-8 (British Academy 2001). A few years ago, the DoE Heritage Service in Northern Ireland (N. Brannon pers. comm.) examined the pros and cons of using video cameras to monitor the condition of nature reserves and other sites. Pros include: • Large savings in person-days and subsistence costs. Staff shortages are acute so using programme monies can be the best way to manage financial resources. • Video record of condition of entire site at the time of the survey. This also allows basis for comparisons. • Copies of videos can be supplied to HQ and other organisations who would find the information useful. • Photographs can be taken from the air which are useful for condition monitoring work, slide shows and publications. • More sites can be covered in good conditions, suitable for covering significant areas. Cons are that: • Flights are expensive: e.g. for Lough Neagh area, a flight is roughly 50% more expensive than ground-based vehicle costs. • • • The helicopter method is more dependent on good weather conditions than ground-based survey. There is less scope for detailed examination of sites. Contact with landowners is lost. • If hire of a photographer and video equipment is involved, extra costs can also include larger helicopter (c. Stg£100/hr extra). In the example modelled, it was reckoned that a single helicopter flight costing c. Stg£1,340 in travel costs could achieve a saving of about Stg£5,000 on fieldwork that otherwise would take two people c. 35 days to complete on the ground. However, this was for continuous filming of large areas of nature reserve rather than more isolated sites. The Discovery Programme’s recent experience has been that the basic costs of commissioning a vertical photogrammetry survey is approximately €150-175 per km 2 , excluding software licences and processing costs. Lidar costs are in the order of €800- 1,200 per km but this may be broadly comparable with photogrammetry when processing costs are taken into account. Satellite imagery (true colour at 60cm resolution and minimum of 25km 2 ) is much cheaper (€13.5-15 per km 2 for archive images; €17- 25 for new images, with an extra 25-50% to obtain near cloudless or cloudless conditions) but is significantly more limited in terms of resolution and potential metrical data.
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A I R A N D E A R T H A E R I A L A
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© An Chomhairle Oidhreachta / The
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3.9 Integration with other Types of
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Figure 14: The Discovery Programme
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Figure 39: This vertical photograph
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10 Foreword One of the initiatives
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12 Acknowledgements It would not ha
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14 Key Priorities for Aerial Archae
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16 • A practical handbook in arch
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18 • A series of pilot studies co
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20 5. Any new strategy for reconnai
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22 As a means of discovering archae
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24 Drawing on the work of O.G.S. Cr
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26 2 PRINCIPAL SOURCES OF AIR PHOTO
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28 National Museum of Ireland While
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30 Other material held by the GSI i
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32 Figure 9: An infrared vertical i
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34 The aims and objectives of these
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36 2.5 Private Collections Dr Daphn
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38 2.6 Commercial Collections Two w
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40 Figure 18: Google Earth satellit
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42 3.2 Aerial Platforms The equipme
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44 Figures 20 a-b: The use of ballo
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46 Figure 23: The true form of the
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48 Figure 25: The cumulative impact
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50 3.4 Conventional Photography: Di
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Page 63 and 64: 62 Both Kelleher (1995) and Redfern
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Page 81 and 82: 80 The Archaeology of Lakes, Coast
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Page 87 and 88: 86 Roads The National Roads Authori
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Page 115 and 116: 114 Doody, M G, 1995. ‘Ballyhoura
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Page 119 and 120: 118 Raftery, J, 1951. Prehistoric I
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