GEOM30009: Imaging the Environment
Elements of image interpretation
Kourosh Khoshelham
What do we see in this image?
Vanua Balavu Island, Fiji. Image source: http://www.satimagingcorp.com 2
What do we see in this image?
Vanua Balavu Island, Fiji. Image source: http://www.satimagingcorp.com 3
Airport
runway
Road
Settlements
Clouds
Water
Vegetation
Despite the unusual perspective we can identify many features.
What do we see in this image?
Rockhampton, Queensland, Australia. Image source: NASA/GSFC (Jesse Allen): http://earthobservatory.nasa.gov 4
What do we see in this image?
Rockhampton, Queensland, Australia. Image source: NASA/GSFC (Jesse Allen): http://earthobservatory.nasa.gov 5
Settlements
Clouds
Water
Vegetation
Despite the unnatural colour we can identify many features.
How to visually identify image contents?
Image interpretation cues:
– Tone and colour
– Shape and size
– Texture
– Pattern
– Shadow
– Association
– Time and location
Image interpretation
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• Tone and colour
Image interpretation cues
Different features have
different tone (in grayscale
images) and colours (in
colour images).
Here water, vegetation
and built-up areas have
distinctly different colours.
Image source: Satellite Imaging Corporation http://www.satimagingcorp.com 7
• Shape and size
Image interpretation cues
Different features
have different
shapes and sizes.
Here the shape
and size of the
crown helps
identify the
deciduous and
coniferous trees.
Image source: http://www.bing.com/mapspreview
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• Texture
Image interpretation cues
Some features
have a distinct
texture.
Here sand appears
smooth, while
dunes have a
rougher texture.
Image source: Bing Maps
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• Pattern
Image interpretation cues
Some features
have distinct
patterns.
Here center pivot
irrigation areas
create a pattern of
circles.
Image source: Google Earth
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• Shadow
Image interpretation cues
Objects above the
ground surface
cast a shadow.
Here shadow
helps recognize
the skyscraper.
Image source: http://www.bing.com/mapspreview
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• Association
Image interpretation cues
Some features are associated with certain other features.
This building is most likely a school since a playground is usually
associated with a school.
Image source: http://www.bing.com/mapspreview
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• Time and location
Image interpretation cues
Some features appear in
certain times or locations.
Knowing that these images
were taken over Yukon
river in Alaska makes it
easier to identify snow (light
blue) on the mountains
around the river.
Image source: NASA images courtesy Jeff Schmaltz http://earthobservatory.nasa.gov 13
Example: interpreting images of Mars
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Basic facts about Mars:
• Twice the size of Earth’s moon; land area size similar to Earth
• Cold and dry; temperature ranges from -128 C to 27 C
• Thin atmosphere; mainly carbon dioxide
• Has mountains, volcanos, canyons, deserts and polar ice caps.
Interpreting images of Mars
• Polar ice caps
• Identified by tone, texture, and location
• Composed of water ice, carbon dioxide ice (dry ice) and dust
South Polar Cap of MarsNorth Polar Cap of Mars
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Interpreting images of Mars
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• Impact craters
• Identified by shape, shadow, and
association (with thin atmosphere)
• The density of craters can be used
to estimate the age of the surface.
• Calibration by known age of
samples from the moon.
• Low accuracy due to influence of
secondary craters.
Image credit: NASA/JPL-Caltech/ASU
Interpreting images of Mars
• Valley network
• Identified by shape,
pattern, and shadow
• Evidence for erosion
• Associated with fluid on
the surface in the past.
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Interpreting images of Mars
• Dust whirlwind on Mars
• Identified by shape,
colour, texture, and
shadow
• The length of the
shadow can be used to
estimate the height of
the plume (about 800 m
here).
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Image credit: NASA/JPL-Caltech/Univ. of Arizona
0 m 50 m 100 m
Interpreting images of Mars
• Mesa development on Mars
• Mesa: flat-topped hill with steep
sides, evidence for layers of rock
Source: pubs.usgs.gov/sim/3079/sim3079_map.pdf
• Tone and shadow are indicators of
the elevated region (compare
shadows around the craters and
the mesa).
• What indicates elevation (why can’t it
be a rectangular depression?!)
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Summary
• Image interpretation: visual identification of
image features.
• Image interpretation cues:
➢ Tone and colour
➢ Shape and size
➢ Texture
➢ Pattern
➢ Shadow
➢ Association
➢ Time and location
• But why in some images features appear in
unnatural colours?
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© Copyright The University of Melbourne 2011

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