Introduction to Digital Elevation Title Models (DEMs)...Elevation Data –Feb 2000 •SRTM mapped...
Transcript of Introduction to Digital Elevation Title Models (DEMs)...Elevation Data –Feb 2000 •SRTM mapped...
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TitleName name name
Introduction to Digital Elevation Models (DEMs)
Harry West
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Terminology - DEMs
DTM DSM
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History of DEM Development
• More traditional methods of DEM creation: interpolation of printed contour lines and manual photogrammetry
• RS approaches started to develop during the Cold War Period (1980’s)• Driven by a military requirement
• Missile guidance systems required rapid high quality elevation data
• SPOT-1 (1986) first commercial digital stereo imagery
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History of DEM Development
• Turn of the Century saw technology continue to improve enabling a range of elevation data solutions
NASA TERRA Satellite (1999)
ASTER SensorAdvanced SpaceborneThermal Emission and Reflection Radiometer
IKONOS (1999)
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Stereo Imaging
• The primary advantage of stereo imagery is the ability to extract geographic features in 3D such as buildings, roads, manmade structures and other terrain features
• Terrain slope conditions of <20%
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Space Shuttle Radar Topography Mission (SRTM)
• One of the biggest milestones in RS Elevation Data – Feb 2000
• SRTM mapped all land surfaces between +/- 60 degrees over 10 days
• Driven by military requirements
• First global scale elevation model (90m –30m resolution)
• Only active C-, L-, X-Band sensor
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TanDEM-X (2010)
• Add on mission to TerraSAR-X (2007)
• 12 m gridded model ‘WorldDEM’
• Processed over about 3 years, this data was designed to provide a step up from SRTM, covering the high latitudes, increasing the detail and filling SRTM voids
• Based on Synthetic Aperture Radar (SAR) principle
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• One satellite acts as a transmitter to illuminate a common radar footprint
• The scattered signal is recorded by both satellites simultaneously
• This simultaneous data acquisition makes dual use of the available transmit power and helps avoid potential errors
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SR
TM
vs
Tan
DE
M-X SRTM = 30m Res WorldDEM = 12m Res
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SR
TM
vs
Tan
DE
M-X
SRTM = 30m Res WorldDEM = 12m Res
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Light Imaging Detection & Radar (LiDAR)
• Measuring the location of objects from a known point
• The known point is mounted on a moving aircraft or helicopter (platform)
• The measuring device is the ‘reflection’ of a beam of light off the target feature
• You need to be able to measure and capture location extremely quickly and efficiently
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Raw
LiD
AR
: P
oin
t C
lou
d • A large data set of points
• Elevation information
• Intensity information
• Return information
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Higher Resolution = “Better” Data?
LiDAR DEMs 25cm-2m
Just because they are higher resolution
doesn't mean they are perfect
Need to manage expectations of
realism (Dottori et al., 2013)
Hyper-resolution Ignorance ! (Beven et al., 2015)
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Dig
ital
Ele
vati
on
Mo
dels
&
‘U
ncert
ain
ty’
This can lead to inaccurate representations of reality
Impact on management decisions?
There is inherent error which constitutes uncertainty in the data
When working with DEMs the accuracy with which the topography was mapped with affect the output of any results
Satellite accuracy? Aircraft accuracy?
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Vert
ical
Accu
racy /
Err
or
4.0maOD
5.0maOD
6.0maOD
RMSE = 1m
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Vis
uali
sin
gU
ncert
ain
ty
West, H. , Horswell, M. and Quinn, N. (2018) Exploring the sensitivity of coastal inundation
modelling to DEM vertical error. International Journal of Geographical Information Science, 32 (6).
pp. 1172-1193. ISSN 1365-8816
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DEM Hydrological Functions (ArcMap)
Original DTM
FillFlow
DirectionFlow
AccumulationDrainage
Area
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Flo
w D
irecti
on
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Flo
w A
ccu
mu
lati
on
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DEM Hydrological Functions (ArcMap)
Original DTM
FillFlow
DirectionFlow
AccumulationDrainage
Area