Aerial Archaeology in Ireland - The Heritage Council

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3.3 Conventional Photography: Geographical Limitations and Potential Over the whole of Ireland, archaeological sites survive as earthworks and structures that can be recorded, analysed, interpreted and illustrated using aerial survey. Aerial photography has a particular role in helping to identify features that may be difficult to see on the ground, and where a clearer view of their context assists identification (e.g. slight traces of field systems, small low barrows where viewing of stereoscopic photography or low-level lighting coupled with low vegetation enhances visible relief). The visibility of features from the air is enhanced by careful timing to coincide with times when vegetation is low, weather is clear, and the sun is low in the sky. This can be enhanced by extreme weather conditions (drought, frost or snow). Lidar techniques (see below) overcome several of these limitations, although they are relatively expensive. In many areas, particularly on poorer soils and where agriculture has not been intensified (or in the case of the Burren where ancient land use led to soil depletion), archaeological survival is particularly high. In such areas, there tends to be a more complicated palimpsest of overlain remnant features than elsewhere. These reflect long-term changes in land-use practice, with the traditional idea of discreet archaeological ‘sites’ becoming increasingly dubious. Aerial archaeology is especially well-suited to providing the basis for landscape interpretation in these areas (Herity 1987, 1988; Barrett 1997/8, forthcoming b; Kelleher 1995). Barrett (1993; 1997b; 1997/8) has used air photography in Kerry, Roscommon and elsewhere to show how vulnerable such palimpsests are to agricultural clearance (Figure 22). J.K. St Joseph (Norman and St Joseph 1969) graphically revealed how formerly upstanding sites that have been flattened by ancient or recent agricultural clearance are still detectable as sub-soil remains which are revealed by crop and soilmarks in the tillage counties of eastern and southern Ireland (Figure 23). Although no longer upstanding, such remains nevertheless add significantly to the overall archaeological resource and its potential for research (Barrett 1980, 1982b, 1984). Figures 22 a-b: Improved and unimproved fields at Brideswell, Co. Roscommon (Gillian Barrett, May 1991) 45
46 Figure 23: The true form of the large trivallate barrow at Fenniscourt, Co. Carlow, was revealed by air photography which captured the cropmark evidence of three ditches surrounding the upstanding tumulus (CUCAP 16 July 1971) As noted above, the aerial survey of earthworks can be enhanced by choosing ideal timing and weather conditions (e.g. Figures 24, 27, 28). Cropmarks, however, are even more dependent on climate and seasonal weather patterns, as well as cropping patterns, for their appearance. Soil moisture deficit is a crucial factor. This varies on a highly seasonal basis, from one year to another, and from one locality to another. Coupled with variations in cropping patterns, this makes the appearance of cropmarks highly capricious.
Page 1 and 2: A I R A N D E A R T H A E R I A L A
Page 3 and 4: © An Chomhairle Oidhreachta / The
Page 5 and 6: 3.9 Integration with other Types of
Page 7 and 8: Figure 14: The Discovery Programme
Page 9 and 10: Figure 39: This vertical photograph
Page 11 and 12: 10 Foreword One of the initiatives
Page 13 and 14: 12 Acknowledgements It would not ha
Page 15 and 16: 14 Key Priorities for Aerial Archae
Page 17 and 18: 16 • A practical handbook in arch
Page 19 and 20: 18 • A series of pilot studies co
Page 21 and 22: 20 5. Any new strategy for reconnai
Page 23 and 24: 22 As a means of discovering archae
Page 25 and 26: 24 Drawing on the work of O.G.S. Cr
Page 27 and 28: 26 2 PRINCIPAL SOURCES OF AIR PHOTO
Page 29 and 30: 28 National Museum of Ireland While
Page 31 and 32: 30 Other material held by the GSI i
Page 33 and 34: 32 Figure 9: An infrared vertical i
Page 35 and 36: 34 The aims and objectives of these
Page 37 and 38: 36 2.5 Private Collections Dr Daphn
Page 39 and 40: 38 2.6 Commercial Collections Two w
Page 41 and 42: 40 Figure 18: Google Earth satellit
Page 43 and 44: 42 3.2 Aerial Platforms The equipme
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Page 51 and 52: 50 3.4 Conventional Photography: Di
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Page 75 and 76: 74 Roles and potential for historic
Page 77 and 78: 76 4.2 Roles in Supporting Archaeol
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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
Page 89 and 90: 88 Pipelines The general principles
Page 91 and 92: 90 General Development Where there
Page 93 and 94: 92 ‘…numerous sites in pasture
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96 Designed Landscapes and Conserva
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98 showing the clear benefits of in
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100 Figure 55: Aerial photograph of
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102 5 QUALITY, RESOURCES AND ORGANI
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104 Estimates of costs per site or
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106 ago in England, may have meant
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108 6 TEACHING AND TRAINING 6.1 Cov
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110 6.2 Other Provisions for Traini
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112 Benson, D and Miles, D 1974. Th
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114 Doody, M G, 1995. ‘Ballyhoura
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116 Twohig and M. Ronayne (eds) Pas
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118 Raftery, J, 1951. Prehistoric I
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120 Colin Shell Cambridge Universit
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Aerial Archaeology in Ireland - The Heritage Council

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