Geography Reference
In-Depth Information
43.3 cover many of the standard tasks typically
undertaken as part of a geographical research
project. These include field mapping (Boxes 43.1
and 43.3), verification of spatial models (Box 43.2)
Box 43.1 Field mapping: geomorphological interpretation with GPS
Glacial terrain is usually mapped from aerial photography
and large-scale topographic maps. However, there are
many formerly glaciated mountain environments where
such data are unavailable or of poor quality. Also, the
difficult terrain often prevents the use of traditional
instrumental techniques. GPS, on the other hand, is
unaffected by these problems and possesses several
advantages to the geomorphologist. For this study, field
mapping was carried out in the Llanberis area of
Snowdonia, North Wales. Snowdonia was chosen as the
study site because of easy field access to its well-known
glacial landforms. This has permitted controlled testing of
GPS. The study site is located in steep terrain, with several
peaks in excess of 1000 metres. The area was previously
glaciated during the Pleistocene and contains a series of
erosional and depositional landform systems (see Addison
et al . 1990; Gray 1982; Gray and Lowe 1982). The work
described here concerns the mapping of the smaller-scale
glacial landforms associated with glaciation during the
Loch Lomond Stadial, such as moraines. Two GPS
strategies were employed to map the glacial landforms:
kinematic DGPS (using pseudoranging) for delineating
landform boundaries and static DGPS (using carrier
phase) to determine the location of sites for further
investigation (Smith et al. 1997).
Figure 43.3 shows the kinematic DGPS data overlain
on an orthophotograph of the same area. The lines on
the map represent the boundaries of different relict
glacial features. Walking around the perimeter of the
landforms and recording their position with a GPS
receiver produced these boundaries. The DGPS method
provided positional accuracies of a few metres (2 m at
best and typically 5-10 metres). However, as the
boundaries between glacial landforms are 'fuzzy' and the
surveyor had to use field cues to determine the boundary
of a particular feature, this level of accuracy was
considered acceptable (Smith et al . 1998). A major
advantage of the kinematic DGPS method was that it
allowed fieldworkers to map features continuously. In
addition, as the data had been collected digitally, they
were easily transferred into a geographical information
system (GIS), where they were checked for accuracy and
used in further quantitative analysis.
Carrier phase DGPS was used to locate field
investigation sites where moraine soil samples could be
taken or former ice flow direction recorded from striae
(ibid.) . Carrier phase observations were accurate to
within a metre (Magellan 1994). These data were also
used to record the location of good exposures for use in
later sedimentological analyses.
Figure 43.3 GPS Iandscape feature map, Snowdonia, North Wales.
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