Flodden 500
Archaeology
Aerial Rectification: Site 2
(20TH AUGUST 2010)
INTERIM REPORT 2
1st September 2010
Flodden 500 Archaeology
CONTENTS
1.
Introduction ........................................................................................................ 2
2.
Flodden Hill: Site 2 ............................................................................................ 4
2.1
Photo 1 (Figure 3) ................................................................................... 4
2.2
Photo 2 (Figure 4) ................................................................................... 6
2.3
Initial Interpretation of Site 2 ................................................................. 6
3.
Method ................................................................................................................ 8
4
Results.................................................................................................................. 10
Acknowledgements
Flodden 500 Archaeology would like to acknowledge Remembering Flodden for their
continued permission to use the battle image (header and frontis piece) in this report,
and Roger Miket who provided the photos referred to below as Photo 1 and Photo 2
and who has supported the project with his advice and ideas since its inception in
2009.
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FLODDEN 500 ARCHAEOLOGY:
INTERIM REPORT 2
AERIAL PHOTOGRAPHIC RECTIFICATION: SITE 2
1.
INTRODUCTION
As part of the wider, ongoing archaeological study of the wider landscape of the
Battle of Flodden (Figure 1), aerial photographic rectification was carried out on
two photographs taken by Roger Miket during a general reconnaissance flight of
northern Northumberland during July of 2006.
The summer of 2006 proved to be an exceptional year for crop mark visibility with
many buried sites being recorded and photographed for the first time, and others
already recognised being recorded in a level of detail only previously rivalled by the
photos taken during the exceptional year of 1947. Many sites were so prominently
visible as differential marks (wet and dry) within crops that they were visible both
as differential growth and colour at ground level.
Figure 1: The wider context of the Battle of Flodden
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This report addresses the processes, methodologies and results of a programme of
‘rectification’ of these two photos carried out during August of 2010. Rectification
is necessary where a photo is taken at an oblique angle (rather than vertically). Such
oblique photography is usual when a flight is made at low level to allow maximum
detail to be recorded whilst still photographing as much of, or the whole, of a site as
is possible.
The disadvantage of oblique photography is that the results can not immediately be
scaled or located on a map for the purpose of establishing exact locations of features
recorded in the photograph. This is the case as oblique photography creates a
parallax distortion of the site it is recording.
In the case of Flodden Hill Site 2 this distortion is further increased by the feature’s
location on the top edge of a steep north facing slope.
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2.
FLODDEN HILL: SITE 2
Site 2 at Flodden Hill was initially identified by Roger Miket during July of 2006.
Two photographs taken by Roger at that time show a rectangular enclosure with
what appears to be a substantial ditch surrounding various internal features. This
enclosure runs roughly from west to east on the north facing crest of the ridge
between Flodden Hill and the King’s Chair (also known as Flodden Edge). Site 2 is
located approximately at NGR NT 908 656 in a field that forms part of Callaburn
Farm.
Figure 2: Approximate location of Site 2
2.1
Photo 1 (Figure 3)
Photo 1, taken from the south looking north clearly shows rectangular darker marks
and linear marks both internally and externally to the main enclosure and what
appears to be a circular or penanular arrangement within the main ‘ditch’ of the
enclosure at its south-eastern corner (bottom right). Photo 1 also clearly shows how
the down slope on which Site 2 is located is distorting the image.
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Figure 3: Photo 1 of Site 2 taken from the south looking north during July 2006
Figure 4: Photo 2 of Site 2 taken from the east looking west during July 2006
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2.2
Photo 2 (Figure 4)
Photo 2, taken from the east looking west also shows rectangular darker marks and
linear marks both internally and externally to the main enclosure and what appears
to be a circular or penanular arrangement within the main ‘ditch’ of the enclosure at
its south-eastern corner (bottom left). Photo 2 would ultimately prove easier to
rectify using the AirPhoto Software as it had 5 clear control points and the distortion
caused by slop was reduced due the photographer’s location looking across the
contours rather than down them.
2.3
Initial Interpretation of Site 2
While the form of site 2 immediately led to its classification as an Iron Age
enclosure typical of such rectangular features seen around Northern
Northumberland and the Scottish Borders, closer analysis of the site’s features lead
to this interpretation being questioned because:
 The shape and size of the feature are unusual
 The entrance visible in the east end is unusual
 The site’s location just off the crest of a north facing ridge is unusual
These factors in concert with its location on Flodden Hill have led to the suggestion
that this feature may actually be part of the defensive works established on this site
during the first week of September 1513 by the Scots army of James IV prior to the
battle of Flodden (September 13, 1513).
The presence of a second similar feature, Site 3 (to be subject of a separate analysis)
(figure 5) located on the southern slopes of the same ridge, less than 500 metres to
the south is also of interest and suggestive of an integrated circuit of defensive
redoubts around Flodden Hill.
Excavations scheduled for September 2010 should help to characterise not only the
form of the remains recorded in the two 2006 photographs but also their date.
Whether they are of Iron Age origin (possibly re-used in 1513) or whether their
construction dates directly to the period of Scottish Military occupation on Flodden
Hill in the early post medieval (16th Century).
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Figure 5: extract from a 1948 vertical aerial photograph taken by the RAF
showing the location of Site 2 (red) and the similar, but south facing Site 3 (blue
circle)
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3.
METHOD
Initially traditional paper methods of rectification were examined. Two methods
were tried on both photographs, these were the paper strip and mobius network
methods. However in the case of both photographs and both methods no suitable
rectification was achieved. This was caused by two primary problems, firstly the
lack of suitable control within the photos (four points are required but only three
suitable points could be identified) and because in both cases at least one of the 3/4
points available was located at the bottom of a very steep slope below the site. This
caused additional distortion to the photographic results that meant that the resulting
rectifications were clearly skewed (Figure 5)
Figure 5: Results of Mobius Network rectification. (Blue= Photo 1. Red and
Orange = Photo 2)
As a result of this obvious skewing of the results generated by the ‘manual’ methods
of aerial photographic rectification it was decided to use specialist software written
specifically to provide rectification of photographs in an archaeological context.
In this case the well established and widely used AirPhoto 3, written and maintained
by BASP (Bonn Archaeological Software Package) of Bonn University in Germany
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was used. This software uses an algorithm to rectify the photos and outputs a
rectified JPG image that can be imported into GIS to be transcribed. The resulting
image and data is not only rectified but also geo-located within the relevant grid
system (in this case Ordnance Survey Grid). In addition to this AirPhoto 3 can also
be programmed with a DTM (digital terrain model) which allows it to take account
of the terrain within which the photograph sits.
In the case of Site 2 this DTM rectification is essential due to the slope that it sits
on. A simple transcribed DTM was achieved using the contour information
available on the Ordnance Survey 1:25000 Explorer series map (339).
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4
RESULTS
Rectification of Photos 1 (Figure 6) and Photo 2 (Figure 7) of Site 2 using AirPhoto
3 produced satisfactory results that led to better transcription of the site location
than could be achieved by mean of a Mobius Netowork. AirPhoto 3 reported
standard deviations (levels of error) of 4 metres for Photo 1 and 2.5 metres for
Photo 2. This suggests that the rectification achieved should be sufficient to make
initial locations of excavation trenches, during September 2010 particularly on the
linear features to the east of the main enclosure.
Figure 8 shows the composite transcription of the two photos (Photo 1 = yellow,
Photo 2 = red). The location of the features from photo 1 can clearly be seen to be
around 4 metres to the north of those from Photo 2. The simple explanation for this
is the nature of the slope and the location of the photographer, looking down it,
when Photo 1 was taken.
Figure 6: Site 2, Photo 1 (from south) geo located and rectified.
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Figure 7: Site 2, Photo 2 (from east) geo located and rectified
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Figure 8: Composite rectification of Photos 1 (yellow) and 2 (red) of Site 2.
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