406
J. Raper et al.
give examples of a optical band videography-draped surface model for vegetated sand
dunes on Scolt Head Island and show the obtained accuracies for this purpose.
Laser surface profiling is a new and promising method of elevation survey
which can be integrated with other remotely sensed imagery captured at the same time
or previously. Using a laser distance measuring device that sweeps back and forwards
over a scene at 80-200Hz relative heights can be determined instantaneously (Lohr,
1997). Used aboard an aerial platform the laser device scans a swath defined by the
forward movement of the aircraft and can be corrected by on-board attitude sensors.
Currently a research technology it is likely to grow in importance rapidly.
Ground survey is the key method of direct landform survey and is usually
based on the observation of points relative to local or national control frameworks.
Typical ground surveys employ a total station with electronic distance measurement
and the computer logging of data points. The horizontal and vertical angles subtended
to the backsight line (a line between 2 known points) and the distance to the surveyed
point are recorded in the data logger. These observations are converted into plane
coordinates by a survey reduction program. Over 20 ground surveys in the form of
point measurements of position and elevation have been collected at Far Point on Scolt
Head Island since 1992, each survey involving the collection of 700-1000 data points
over an area 1km square. The data points collected in these surveys have been located
on the breaks of slopes and crests of the spits in the study area by the survey pole
carrier and assigned a code for the mean grain size of the sediment by visual
inspection. The coordinate frame used is a local coordinate system (the ‘Scoltframe’)
defined by reference to surveyed monuments on the island, but rotations to National
Grid are available. Accuracy is dependent firstly on the fidelity of the ground
monumentation network and secondly on the precision of the instruments: both are
checked frequently in the Scolt Head surveys.
Surface models for the surveys carried out at Scolt Head Island have been
generated using triangulation methods. Triangulation is an exact local surface
modelling method in which the surface is made of inclined triangular elements
constrained by the data points. This method of surface modelling has been used here
and is recommended for assessment of morphological change (as opposed to
visualisation) because the surface fits exactly to the data points with no extrapolation
(Gold, 1989). The data points were selected in the field in order to mimic the surface
morphology as closely as possible and with the exact fit principles of triangulation
representation explicitly in mind.
COASTAL PROCESS DATASETS
Data on wave height and period is sometimes available from direct measurement at sea
and a number of wave platforms and wave buoys are permanently stationed offshore
(see for example http://www.nws.fsu.edu/). This data is rarely if ever gathered in the
nearshore zone close to landforms under study due to the operating constraints in this
area, hence wave shoaling models are required to estimate wave heights at the
shoreline. Wave heights at user-defined points can now be hindcast from wind
J. Raper et al.
give examples of a optical band videography-draped surface model for vegetated sand
dunes on Scolt Head Island and show the obtained accuracies for this purpose.
Laser surface profiling is a new and promising method of elevation survey
which can be integrated with other remotely sensed imagery captured at the same time
or previously. Using a laser distance measuring device that sweeps back and forwards
over a scene at 80-200Hz relative heights can be determined instantaneously (Lohr,
1997). Used aboard an aerial platform the laser device scans a swath defined by the
forward movement of the aircraft and can be corrected by on-board attitude sensors.
Currently a research technology it is likely to grow in importance rapidly.
Ground survey is the key method of direct landform survey and is usually
based on the observation of points relative to local or national control frameworks.
Typical ground surveys employ a total station with electronic distance measurement
and the computer logging of data points. The horizontal and vertical angles subtended
to the backsight line (a line between 2 known points) and the distance to the surveyed
point are recorded in the data logger. These observations are converted into plane
coordinates by a survey reduction program. Over 20 ground surveys in the form of
point measurements of position and elevation have been collected at Far Point on Scolt
Head Island since 1992, each survey involving the collection of 700-1000 data points
over an area 1km square. The data points collected in these surveys have been located
on the breaks of slopes and crests of the spits in the study area by the survey pole
carrier and assigned a code for the mean grain size of the sediment by visual
inspection. The coordinate frame used is a local coordinate system (the ‘Scoltframe’)
defined by reference to surveyed monuments on the island, but rotations to National
Grid are available. Accuracy is dependent firstly on the fidelity of the ground
monumentation network and secondly on the precision of the instruments: both are
checked frequently in the Scolt Head surveys.
Surface models for the surveys carried out at Scolt Head Island have been
generated using triangulation methods. Triangulation is an exact local surface
modelling method in which the surface is made of inclined triangular elements
constrained by the data points. This method of surface modelling has been used here
and is recommended for assessment of morphological change (as opposed to
visualisation) because the surface fits exactly to the data points with no extrapolation
(Gold, 1989). The data points were selected in the field in order to mimic the surface
morphology as closely as possible and with the exact fit principles of triangulation
representation explicitly in mind.
COASTAL PROCESS DATASETS
Data on wave height and period is sometimes available from direct measurement at sea
and a number of wave platforms and wave buoys are permanently stationed offshore
(see for example http://www.nws.fsu.edu/). This data is rarely if ever gathered in the
nearshore zone close to landforms under study due to the operating constraints in this
area, hence wave shoaling models are required to estimate wave heights at the
shoreline. Wave heights at user-defined points can now be hindcast from wind