Aberdeen Institute for Coastal Science and Management, University of Aberdeen Team (alphabetical order): Alastair Dawson Cristina Gomez David Green William

Aberdeen Institute for Coastal Science and Management,University of Aberdeen

Team (alphabetical order):

Alastair DawsonCristina GomezDavid GreenWilliam RitchieAmy TaylorRobert Wright

TERRAIN MODELLING FOR THE ASSESSMENT OF COASTAL CHANGE

Society of Cartographers Annual Summer Conference 2008 (1st September)

Overview


• Background

• Objective

• Location of study sites

• Data used

• Methodology

• ResultsVisualization: DTM, photo mosaics

• Analysis and interpretation:Visual interpretation of geomorphologyPlanimmetric changeVolumetric change

BACKGROUND

OBJECTIVE

•Coastal environment importance: dunes and coast line.

•Lack of data of the causes and rate of change in Scotland’s natural heritage.

•Evidence of morphology change.

Study recent (last decades) changes in beach and dune systems in Scotland

Work done for the project: “Assessment of the rates and causes of change in Scotland’s beaches and dunes” (AICSM for SNH)


SITES LOCATION

Selection criteria:

• Out of human excessive influence

• Areas of submergence and emergence(postglacial)

• Availability of aerial photography:

• two different dates • metric (useful for analytical

photogrammetry)


DATA

Aerial photography: stereo pairs to create the DEM (Digital Elevation Model)-DTM

GCP (Ground Control Points): for photography orientation and aero triangulation

For reference and comparison:Ancillary maps: OS 1800’s coast lines for comparisonRecent maps: OS digital recent maps


METHODOLOGY

Interior orientation

Import frames

Triangulation

Mosaic images DTM creation

Edition

Aerial photos

Ground Control Points Photogrammetry (Socetset)

ASCII to raster

Raster algebra Surface analysis Spatial analysis Visual analysis

Change map Contours Volume Flythrough

GIS (ArcGis)

Export to ASCII


DTM creation

Overlapping60 % end lap30 % lateral


Import frames: Stereo pairs

ComplexityBig areas - many stereo pairsGround Control PointsTie points

Triangulation


• DTM resolution (size of raster cell)

Small enough to capture the variability of the terrain

Big areas-----big files

2-5 m

Important to compare DTMs

Finer resolution tested– disturbances, spikes

• Sources of error

PhotosGCP: 0.1 m------ but good distribution???Algorithms for triangulation and DTM creation

• Accuracy--- Better than 0.5 m

DTM creation

Product: Digital Elevation Model

Sands of Forvie 2001Sands of Forvie 1967

Results


Traditional visualization of height map

Results


Detail of DEM, raster Detail of DEM, contour

3D visualization of height map

DTM: Visualization


Photo draped on DEM


DTM: Visualization

Lucebay parallel dunes Sands of Forvie south dune in 1984 with key contour lines

Photo MosaicsVisualization


Morrichmore in 2005

Analysis and interpretation

Planimmetric change: mapping and comparing lines for different dates

vegetation boundary linezero meter Above Ordnance Datum (0 m line)HWMOST (high water mark ordinal spring tide)

Volumetric change: raster algebra with pairs of DTM for comparison

Visual interpretation of DTMs geomorphology


Visualization


Sandwood Bay in 2004

Analysis: planimmetric change


Culbin Sands







Analysis: planimmetric changePlanimetric changes: zero m AOD line


Volume change calculation: raster algebra

Analysis: volumetric change


Analysis: Volumetric change

Morrichmore map of height change 1967-2005


2D

3D

Visualization of volumetric changes


Scheme of colours:red: erosionwhite: no changegreen: accretion

Analysis: Volumetric change

Flythroughs


Location of areas with major changeEvaluation of change:

erosionaccretion

Interpretation of change, causes:climateothers

Temporal/Permanent

Analysis and Interpretation


Contrast with former studies or theories

Confirmation of hypothesis


Profiles for interpretation

Fo B1

-2

0

2

4

6

8

10

12

14

16

18

20

2 10 18 26 34 42 50 58 66 74 82 90 98 106

Distance (m)

Hei

gh

t (m

)

1967

2001

Fo B2

-2

0

2

4

6

8

10

12

14

16

2 10 18 26 34 42 50 58 66 74 82 90 98 106 114

Distance (m)

Hei

gh

t (m

)

1967

2001

Fo B3

-2

0

2

4

6

8

10

2 10 18 26 34 42 50 58 66 74 82 90 98 106 114

Distance (m)

Hei

gh

t (m

)

1967

2001



Methodology conclusions

Coastal environments present special problems in creation of DTM:

WavesPermanent water

Applicability is conditioned by:

Photography: availability, date, qualityField quality data: GCP

Sources of error: data, algorithms.

Results have to be carefully interpreted and used


Main findings of the project

Scotland’s beaches and dunes are dynamic features and subject to rapid but variable rates of change. Some coastlines are advancing, some retreating.

The main factor affecting the change appears to be sediment availability and recycling.

The most recent tide data points to a typical rise in relative sea across Scotland over the last 150 years of around 30 centimeters.

The geomorphological effects on Scotland’s beaches and dunes of storminess history may be much more important but there is no firm evidence to link this to any long-term rise in relative sea level or any other aspect of climate change.


Thanks for your attention


Documents

Aberdeen Institute for Coastal Science and Management, University of Aberdeen Team (alphabetical order): Alastair Dawson Cristina Gomez David Green William