Aerial Archaeology in Ireland - The Heritage Council

58
The fieldwork showed that the general pattern of scrub growth on the Burren is coincident with the main distribution of
archaeological monuments. Of the recorded monuments, 71% were directly affected by scrub, with the threat increasing. The
field survey of the five 1km squares that were fully examined added 48 new sites to the 40 previously recorded — an increase of
120%. Of the new monuments recorded, 50% are being affected by scrub. In some areas, most were found in open areas because
of the serious difficulty of access and visibility in dense scrub. The report states that
‘…an assessment of the satellite imagery has shown it to be more detailed and clear than the aerial
photography examined but it does not, unfortunately, indicate the extent to which the satellite imagery
increased the number of monuments or locational accuracy or clarity of those known, though it is clear
that the imagery has potential for both, as well as clearly showing innumerable relict boundaries…’
Martin Critchley, seminar presentation December 2005
The aerial and satellite imagery also showed that rates of scrub encroachment had slowed down and then risen rapidly over the
last ten years, from 1.9% per annum in 1974-1995 to 0.8% in 1995-2000 and 5.8% in 2000-2005 (Figure 31b).
The Burren has a density of 4.3 recorded monuments per square kilometre, compared with a national average of 1.4. No other
area has such a high density over such a large area, and this does not include the extensive evidence for the evolution of the
landscape provided by relict boundaries and field systems (ERA-Maptec et al. 2005).
The results of the Burren study demonstrate the need for management plans which protect physical conservation, visibility
and access to this exceptionally rich area. The report recommends further analysis of the satellite imagery, both as the basis
for identifying monuments to be checked and inspected on the ground, and repeated imagery for habitat monitoring. In view
of lidar‘s potential to see through vegetation, and the major effort that would be entailed in carrying out detailed fieldwork,
it would be sensible to do further trials to establish which technique would be best suited to establishing a detailed record
and how far basic monument categorisation could be carried out from such data, including the possibility of using pattern
recognition techniques to assist in this (Redfern 2002).
The study has also shown the more general potential for archaeology to be integrated into imaging which is being carried out
primarily for other purposes, and it is clear that more could be done in his area. For example, remote sensing by satellite is
being used for checking types of crop in cultivation at a single land parcel level. It can also distinguish between rough grazing,
temporary grass, forestry, mineral and peat extraction, and urban development. Since cropping is one of the key factors affecting
archaeological survival (O’Sullivan et al. 2001), this type of data could be combined with archaeological data to map areas under
particular pressures of change, especially from agriculture. The technology includes the capability to map change through time.
A recent project commissioned from the OSi by the Department of Agriculture has been using ortho-photography combined
with satellite imagery to relate boundary loss to land use at the level of single land parcels.
A similar approach can be achieved with aircraft-based thermal imaging equipment such as the Daedulus AADS 1230
Airborne Thermal Line Scanner. This generates thermographic data which can be combined with aerial photography or other
digital GIS data for a range of environmental purposes, including land-use analysis, environmental pollution, energy efficiency
and other resource studies. The Compact Airborne Spectrographic Imager (CASI) is a ‘passive’ sensor which records spectral
radiance in visible and near-infrared wavelengths. The Countryside Survey 2000 in England is an example of strategic landscape
monitoring. It also involved detailed field survey which was based on the integration of thermal imaging of vegetation cover
with a digital terrain model derived from lidar topographical profiling. 10 CASI data were recorded at a 3m spatial resolution,
and in wavebands selected around the red and infrared spectral regions, to give optimum information for vegetation analysis of
568 selected 1km squares and a land cover census of the whole country using satellite data.
10 http://www.cs2000.org.uk/Report_pdf/chap10.pdf