Transcript The Electromagnetic Spectrum • The electromagnetic spectrum is composed of dozens of different bandwidths from gamma waves to radio waves.

The Electromagnetic Spectrum
• The electromagnetic
spectrum is composed
of dozens of different
bandwidths from
gamma waves to radio
waves.
Wavelength versus Frequency
• High frequency is
associated with short
wavelength, whereas
low frequency is
associated with long
wavelength. Short
wavelength EMR is
more prone to being
scattered in the
atmosphere
Atmospheric Scattering of EMR
• Shortwave, high
frequency EMR (ex.
X-ray and gamma
radiation) is scattered
in the thermosphere,
whereas ultraviolet
radiation is scattered
in the stratosphere.
Visible light is
scattered in the
troposphere.
Monochromatic Imagery
• Monochromatic
imagery (aka blackand-white) is a perfect
medium to use when
one needs to rely on
shadow for
interpretation.
Natural Color Imagery
• Natural color
imagery is a perfect
medium to use when
one needs to rely on
shadow for
interpretation.
Thermal Infrared Bandwidth
• Thermal infrared is
often used to detect
change in vegetation
patterns over time.
The following is from
Rondonia Province in
the Brazilian Amazon
Basin. Extensive
clear-cutting of forest
in clearly visible in the
southwest quadrant of
the imagery.
Thermal Infrared (Color-Enhanced)
• This thermal
infrared image of
San Francisco has
been color
enhanced to
highlight areas of
vegetation within
the Bay Area.
Ultraviolet Bandwidth
• Ultraviolet (UV)
photography is often
used to detect manmade structures that
blend into the natural
landscape, or is
beneficial when
overcast conditions
are present, such as
in the example at
right.
Air Photo Interpretation
Principles
Shape
Size
Shadow
Tone/Color
Texture
Pattern
Relationship to Surrounding Objects
• Size: the size of an object is one
of the most useful clues to its
identity. Also, understanding
the size of one object may help
us understand the sizes of other
objects.
• For example, most of us have a
feeling for the size of a baseball
field, and football field. When
we observe these objects on a
photograph, it will help us to
understand the sizes of other
objects on the photograph.
• For example, on another part
of the photograph we have a
trailer park. This could easily
be confused with a parking lot,
but when we understand the
size of the objects we will
realize that the objects in the
trailer park are much too large
to be cars.
• Shape: Shapes can often
give away an object’s
identity. For example, a
cloverleaf is a very
distinctive feature of a
highway, while a stream’s
meandering gives away
its identity.
• And again, the baseball
diamond we just looked at
also has a distinctive
shape.
• Shadow: shadows often give us
an indication of the size and
shape of an object. When we
look at aerial photographs we
often see a vantage point we
are not used to: an overhead
view.
• Shadows can let us “cheat” a
little to see the side of an
object. The photos on the right
show the Cornell Theory
Center, which casts a rather
large shadow, indicating the
building size, and a water
tower on one of the farms on
campus. If you look closely,
you can see the “legs” of the
water tower.
• Shadow: while
shadows are helpful,
they can also be a
hindrance. As we try
to look down into the
gorge on the Cornell
campus, we can see
very little due to the
shadows cast.
• Tone: You can see the
tonal contrast
between Cayuga Lake
and the land area.
Also, there is good
tone representation
for wet or dry soils.
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•
Texture: In this photo we see the
Cornell Plantations and Botanical
Garden, as well as the
experimental agricultural plots.
Especially in the Plantations, you
will see the different textural
characteristics between the mowed
lawns and the grassy areas. Notice
too, the small pond in the
Plantations (an example of tone)
Additionally, around another
natural area on campus you can see
the textural difference of trees vs.
more of a grassland area.
And again, as you look at the
agricultural plots you will notice a
different texture from the forested
areas.
Finally, in the golf course shown
below there are obvious patterns
between managed lawns vs. the
unmanaged lawns, in addition to
the tonal differences between the
lawns and sand traps.
• Pattern: There are so
many examples related to
pattern. These would
include the rectilinear
pattern of the older, urban
neighborhoods in Ithaca,
the straight lines of trees
in an orchard, the
rectilinear shape of the
experimental agricultural
plots, and the
configuration of a parking
lot.
• Also, the pattern of the
golf course with greens,
tees, traps, and fairways is
very easy to spot.
• Pattern: the drainage
pattern for a particular
property on this photo is
easy to see. Also, because
the drainage is relatively
straight, we can assume
that a moderate to steep
slope exists, as water did
not have much
opportunity to meander.
• Relationship: observing
relationships on photographs is
one of the most fun
observations. For example, a
school and a plaza are
interpreted differently due to
relationships:
– While both have many
large structures on them,
schools typically have
playing fields
– Also, plazas usually have
larger parking areas
• Here we see the East Hill
Shopping Plaza (no athletic
fields, but a campus of
buildings), and the Ithaca High
School campus (with athletic
fields)
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Relationship: here is another
example of relationship that
shows a middle school and an
elementary school. Notice that it
have buildings like the high
school, and a parking lot, but no
real athletic fields to speak of.
What it does have, however, is
what appears to be a playground,
and is surrounded by a
residential community.
The structures on the top are an
apartment complex. They could
be tractor trailers, but “size”
gives them away. They are too
large to be tractor trailers when
you consider the size of the
schools below.
Notice that just north of the
apartment complex is a large
pool. How do we know it’s a
pool, well, the tone gives us a
clue…
Apartments
School
School
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•
Putting it together: there was a
Broadway musical about George
Seurat, the French painter who
painted with dots. One of the hit
songs was called “Putting it
Together”, and a line was “bit by bit,
putting it together”. In many ways,
photo interpretation is putting
together our observations bit by bit
to form a coherent understanding of
the image. For instance, identifying
the water treatment plant forces us
to use shape, pattern, tone, and
relationship to make the connection:
– We see the water holding areas
in black (tone)
– We see the large tanks (shape)
– And when you’ve seen one
treatment plant, you’ve seen
them all (pattern)!!
Notice that across the water is a
park. Why do we know it’s a park?
Well, again, we see multiple ball
fields, not enough buildings to be a
school, and a very large pool.