In: Wagner W., Szekely, B. (eds.): ISPRS TC VII Symposium - 100 Years ISPRS, Vienna, Austria, July 5-7, 2010, IAPRS, Vol. XXXVIII, Part 7B
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particularly useful in areas with a large percentage of mixed or
deciduous woodland; it is less effective in dense conifer
plantations and indeed is only really successful if flown at the
correct time of year when there is minimal vegetation cover.
When used in the right conditions, however, the results can be
dramatic. Savemake Forest is an area of ancient woodland that
had been established as a royal hunting forest by the time of the
Domesday survey in 1068. It is now an area of largely
deciduous woodland managed by the Forestry Commission
covering an area of some 40 sq kms that is used both as a
timber resource and as an area for recreation. As part of a new
management plan the Forestry Commission decided to
commission a lidar survey to record the area and English
Heritage worked in partnership with them to map the area as
part of the National Mapping Programme (NMP) (Bewley 2001
& 2003). Using a combination of lidar data and traditional
aerial photographs, including historic imagery dating back to
the 1930s, over 300 new sites were recorded, doubling the
number of known features in the survey area. Some of the most
important sites recorded were a potential early roman temple
complex and several new prehistoric settlement enclosures (Fig
1). As well as these entirely new features the survey also added
considerable detail to the Roman roads that run through the
survey area (Crutchley et al 2010).
Figure 1 - A late Iron Age enclosure in Savernake
Forest seen in first return (left) and last return (right)
lidar data, (lidar © Forestry Commission; source,
Cambridge University ULM (May 2006)).
3.2 Uplands
The other sphere where lidar has proven to be particularly
useful is in areas of extensive upland archaeology. This is rather
different from woodland survey where lidar allows the
recording of features that would otherwise be extremely
difficult even to see, let alone record; in upland areas the
features are generally visible on the ground and could be
recorded using traditional techniques, but the use of lidar makes
surveying much quicker and more efficient. An area of the
North Pennines is being mapped as part of a multi-disciplinary
project entitled “Miner-Farmer landscapes of the North
Pennines Area of Outstanding Natural Beauty (AONB)” that
evolved from the management plan for the AONB. The
landscape is sparsely settled with considerable height variation
between the valleys and the unenclosed moorland The area is
being surveyed using a combination of lidar and other remote
sensing techniques and then mapped as part of NMP using a
combination of this data and what traditional aerial photography
of the area exists. Detailed analytical fieldwork is then being
undertaken for the core project area, taking printouts of the lidar
data and desk based interpretations into the field for further
analysis as well as identifying features not seen on the lidar
data. Apart from revealing features that are difficult to identify
on much of the traditional aerial photography, the lidar data is
also proving useful as it provides an extremely accurate base
map against which other sources can be registered and mapped
(Fig 2).
Figure 2 - Using lidar as control
Lidar also allows the accurate mapping of extensive features
such as the remains of the mining industry that would otherwise
take a long time to survey on the ground and therefore enables
field survey time to be concentrated on those areas identified as
most important or too confusing from the lidar data alone.
3.3 Environment Agency standard image tiles
Whilst English Heritage has mainly been working with the lidar
data specifically captured with archaeological use in mind, we
have also been examining the use that can be made of the
readily available data that has been collected by other agencies
for non-archaeological use. The largest example of this in the
UK is the Environment Agency, the body with the role “to
protect and improve the environment, and to promote
sustainable development”. One of their key areas of interest
relates to flood management and to this end they have been
carrying out lidar surveys around the UK for over ten years;
they have concentrated mainly on the coast and major river
valleys to record the topography and how this relates to possible
flooding. They have established a reference archive of lidar
derived imagery as a series of georeferenced image tiles
covering on average 1 - 4 sq km. These tiles are created as
hillshaded images and are colour coded according to a
consistent set of height gradients. On first viewing, often these
do not reveal very much archaeological information, but with a
little simple manipulation within Adobe or another standard
image processing program it is possible to bring out features of
archaeological interest not necessarily visible on standard aerial
photographs. Although this is not as effective a method as full
manipulation of the source lidar data, it does provide a quick
and easy way into the data that is useful for preliminary
archaeological survey.