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Dr. GarverGEO 420
Radiation that
reaches that surface
interacts with targets
in 3 ways:
Absorption(A),
transmission(T),
reflection (R).
Absorption(A)
Transmission(T)
Reflection (R).
Proportions of each
depends on of
energy and what the
target is.
Reflection (R) - radiation "bounces" off target and is redirected.
Radiation reflected from targets is what we are most interested in.
Two types - Specular reflection and Diffuse reflection.
Represents the two extreme ends of the way in which energy is
reflected from a target.
Smooth surface (road) - specular or mirror-like reflection where all (or
almost all) of energy is directed away from surface in a single direction.
Rough surface (tree) - diffuse reflection occurs, energy is reflected
almost uniformly in all directions.
Most earth surface features lie somewhere between, depends on the
surface roughness of the feature in comparison to the wavelength of
the incoming radiation.
Electromagnetic Spectrum: Spectral Signatures
For any material, the amount of solar radiation that it
reflects, absorbs, transmits, or emits varies with
wavelength.
When that amount (usually represented as a %)
coming from the material is plotted over a range of
wavelengths, the connected points produce a curve
called the material's spectral signature (spectral
response curve).
Spectral Signatures
Plot variations of reflected EMR as
a function of wavelength.
Identify and separate different
materials using multispectral data.
Short wave ir
Visible (Vis) 0.4. – 0.7 m
Near Infrared (NIR) 0.7 – 1.3 m
Shortwave Infrared (SWIR) 1.3 – 3.0 m
LK 2 handoutEqn 1.6 pg. 12
EI = ER + EA + ET
Fig. 1.6
LK 2 handoutEqn 1.8 pg. 14Energy of reflected from object x 100 = ______%Energy of incident from object
Fig. 1.8, 1.9, 1.10 (1.10 is similar to graphs in this ppt)
*Important to know typical spectral signatures for vegetation, water and soil!
Fig. 1.8 L&K 2
General example of a reflectance plot for some (unspecified) vegetation type with the dominating factor influencing each interval of the curve indicated:
Vegetation – LK2Visible - Chlorophyll absorption in blue
and red, reflection in green.Near IR (0.7 – 1.3 um) – reflectance
increases dramatically, plant leaf reflects 40 – 50%, absorption is minimal so remainder is transmitted.Reflection is due to the internal structure of
plants.Allows discrimination of speciesPlant stresses – alters reflection
Vegetation – LK2
SWIR (1.3 – 3.0m) - incident energy is absorbed or reflected, little is transmitted.
Water absorption bands in this range
Soil – LK2Considerably less peak and valley variations
in reflectance.Factors that influence soil reflectance act
over less specific spectral bands.Factors – moisture, soil texture, organic
matter, iron oxide.
Short wave ir
Water – LK2Most distinctive characteristic is absorption
at near IR and beyond.Delineate water bodies using near IR But look at water quality/clarity/biology in
the visible
Water: Longervisible and near IR absorbed, reflectance of blue or blue-green
Water and vegetation may reflect somewhat similarly in the visible wavelengths but are almostalways separable in the infrared.
Short wave ir
Landsat Bands
The spectral
response for
inorganic
materials is
distinct from
vegetation types.
Gradual rise in
reflectance with
increasing
wavelengths.
Concrete, light-
colored and bright,
has higher % refl
than dark asphalt.
Refl for veg. rises
abruptly at ~0.7 µm,
followed by a
gradual drop at
about 1.1 µm.
0.3 - 0.5 µm - most veg. types similar in response
0.5 - 0.6 µm moderate variations
0.7 - 0.9 µm - maximum variability
(optimum discrimination)
Sensors
operating in
green, red, and
near IR can
discriminate
absorption and
reflectance of
vegetation.
GR
EE
N
RE
DN
IR
BL
UE
RE
FL
GR
EE
N
HIG
HL
Y R
EF
L N
IR
SUN
SENSO
R
Absorption in red & blue by chlorophyll
pigments.
Reflectance concentrated in the green.
Thus, most vegetation has a green-leafy
color.
Strong reflectance between 0.7 and 1.0
µm (near IR) in cells located in the
interior or back of a leaf.
Intensity of this reflectance is greater
than from most inorganic materials.
So, vegetation appears bright in the near-
IR
Near Infrared Composite (4,3,2)
Adding near
infrared (NIR)
band, drop
visible blue
band
Landsat Bands
Landsat Thematic Mapper BLUE (0.45-0.52 µm): water penetration, soil/veg.
discrimination.
GREEN (0.52-0.60 µm): green reflectance peak for
discrimination and vigor assessment.
RED (0.63-0.69 µm): chlorophyll absorption for species differentiation.
NEAR IR (0.76-0.90 µm): determining vegetation types, vigor, and
biomass content, delineating water bodies, soil moisture.
One of the most successful applications of
multispectral space imagery is monitoring
the state of the world's agricultural
production.
Major crops: wheat, barley, millet, oats,
corn, soybeans, rice.
4 spectral curves
Variations in depths of absorption bands.
If the spectral curves are so similar, how can we
hope to distinguish them in the field?
Characteristic leaf or frond shape will differ
geometrically from most other types.
Oat hay and potato as crops are clearly
dissimilar in the way they look in bulk.
Combination of spectral response and diversity
of shape produce slightly different signatures,
mainly in the depth of any absorption features.
Some crops distinguishable by separations in 0.56 to 0.66 µm interval.
San Joaquin Valley –
July 1972 - barley,
alfalfa, sugar beets,
beans, tomatoes,
cotton.
Yellow-brown and
blue areas flanking
Valley crops are
grasslands and
chapparal.
Blue areas –
Stockton/Modesto.
Spectral signatures for healthy, stressed, and severely
stressed vegetation.
Visible-spectral signatures similar.
Near-infrared -spectral signatures very different.
Healthy vegetation - highest reflectance
Severely stressed vegetation - lowest reflectance.
Which region of the spectrum shows
the greatest reflectance for;
grasslands
pinewoods
red sand
silty water
Spectral Signatures of 4 MaterialsBand 1 = 0.55 um Band 2 = 0.85 um
Vis 0.4. – 0.7 mNIR 0.7 – 1.3 mSWIR 1.3 – 3.0 m
Different materials,
amount of solar radiation that it reflects,
absorbs, or transmits varies with
wavelength.
Important property of matter,
makes it possible to identify different
substances, or classes, and separate them
by their spectral signatures.
Method for measuring differences
Use reflectance differences to distinguish
the four common surface materials
Plot the reflectance percentages of the 4
classes at two wavelengths where there is
maximum differences observed in the
spectral signatures.
Spectral Signatures of 4 MaterialsBand 1 = 0.55 um Band 2 = 0.85 um
Vis 0.4. – 0.7 mNIR 0.7 – 1.3 mSWIR 1.3 – 3.0 m
GL = grasslands PW = pinewoods RS = red sand SW = silty water