402
J. Raper et al.
Data Sources for Spatio-Temporal Analysis of Changing Coastal Terrain
MAPS AND CHARTS
Maps and charts contain much valuable information for the study of geomorphological
change. However, the update cycles of mapping/hydrographic agencies are not usually
appropriate to the timescales of geomorphological investigations and the precise
nature/time of the update may not be documented in full for the end user. Furthermore
the mapping of coastal landforms or mean tide lines and the sampling of sedimentary
materials is carried out for navigation, asset recording or leisure information and not
for geomorphological purposes. Many of the mapped features are interpreted from air
photography and are not formally defined for the end user. As a consequence maps
and charts are probably most valuable in the coastal zone as a source of control
information and the positions of fixed assets/buildings. The researcher must in most
cases collect information on geomorphology as and when needed.
COASTAL FORM AND COMPOSITION
Data on the shape/composition of landforms at the coast can be obtained directly and
indirectly. Indirect methods include satellite remote sensing, aerial photography,
aerial videography and laser surface profiling. Satellite remote sensing can currently
provide multispectral imagery at up to 10m pixel resolution (in panchromatic form),
although several new sources at 1m resolution will become available within the next
couple of years. Satellite remote sensing is expensive to purchase and the user
generally has no choice about the time of capture: Fig. 2 shows 10m panchromatic
SPOT data for Far Point on Scolt Head Island which was taken at high tide, therefore
concealing the whole intertidal area. Elevation data can be derived from satellite
interferometry with l-2m accuracy but must be averaged over the area of the
horizontal pixel. Hence where the surface slope is high, interferometry will have a
lower accuracy due to the areal averaging effect (Zebker et al., 1994). Satellite remote
sensing also provides access to multispectral reflectance data that can be used to
distinguish between sediment composition and vegetated areas.
By comparison, aerial photography is cheaper to purchase from archival
collections and is available at a variety of scales down to a pixel size of centimetres,
although almost all the data is from the optical band. The main drawback in its use is
that it is usually collected according to logistical priorities rather than research
priorities, hence the state of the tide seen in photography of the coast is often less than
ideal. It is also rarely collected at geomorphologically significant intervals such as
immediately after storms as it is expensive to commission. Experiments with the use
of model aeroplanes are an exception to this rule (Green and Morton, 1994)
J. Raper et al.
Data Sources for Spatio-Temporal Analysis of Changing Coastal Terrain
MAPS AND CHARTS
Maps and charts contain much valuable information for the study of geomorphological
change. However, the update cycles of mapping/hydrographic agencies are not usually
appropriate to the timescales of geomorphological investigations and the precise
nature/time of the update may not be documented in full for the end user. Furthermore
the mapping of coastal landforms or mean tide lines and the sampling of sedimentary
materials is carried out for navigation, asset recording or leisure information and not
for geomorphological purposes. Many of the mapped features are interpreted from air
photography and are not formally defined for the end user. As a consequence maps
and charts are probably most valuable in the coastal zone as a source of control
information and the positions of fixed assets/buildings. The researcher must in most
cases collect information on geomorphology as and when needed.
COASTAL FORM AND COMPOSITION
Data on the shape/composition of landforms at the coast can be obtained directly and
indirectly. Indirect methods include satellite remote sensing, aerial photography,
aerial videography and laser surface profiling. Satellite remote sensing can currently
provide multispectral imagery at up to 10m pixel resolution (in panchromatic form),
although several new sources at 1m resolution will become available within the next
couple of years. Satellite remote sensing is expensive to purchase and the user
generally has no choice about the time of capture: Fig. 2 shows 10m panchromatic
SPOT data for Far Point on Scolt Head Island which was taken at high tide, therefore
concealing the whole intertidal area. Elevation data can be derived from satellite
interferometry with l-2m accuracy but must be averaged over the area of the
horizontal pixel. Hence where the surface slope is high, interferometry will have a
lower accuracy due to the areal averaging effect (Zebker et al., 1994). Satellite remote
sensing also provides access to multispectral reflectance data that can be used to
distinguish between sediment composition and vegetated areas.
By comparison, aerial photography is cheaper to purchase from archival
collections and is available at a variety of scales down to a pixel size of centimetres,
although almost all the data is from the optical band. The main drawback in its use is
that it is usually collected according to logistical priorities rather than research
priorities, hence the state of the tide seen in photography of the coast is often less than
ideal. It is also rarely collected at geomorphologically significant intervals such as
immediately after storms as it is expensive to commission. Experiments with the use
of model aeroplanes are an exception to this rule (Green and Morton, 1994)