Spectral Signatures: Vegetation, Soil, Rock

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Spectral Signatures Vegetation, Soil, Rock

• Dr. Garver
• GEO 420

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Radiation that reaches that surface interacts
with targets in 3 ways Absorption(A),
transmission(T), reflection (R).
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Absorption(A) Transmission(T) Reflection
(R). Proportions of each depends on l of energy
and what the target is.
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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.
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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.
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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).

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 Spectral Signatures

• Plot variations of reflected EMR as a function of
  wavelength.
• Identify and separate different materials using
  multispectral data.

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Short wave ir
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• Visible (Vis) 0.4. 0.7 mm
• Near Infrared (NIR) 0.7 1.3 mm
• Shortwave Infrared (SWIR) 1.3 3.0 mm

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LK 2 handout

• Eqn 1.6 pg. 12
• EI ER EA ET
• Fig. 1.6

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LK 2 handout

• Eqn 1.8 pg. 14
• Energy of l reflected from object x 100
  ______
• Energy of l 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!

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Fig. 1.8 LK 2
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General example of a reflectance plot for some
(unspecified) vegetation type with the dominating
factor influencing each interval of the curve
indicated
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Vegetation LK2

• Visible - 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 species
• Plant stresses alters reflection

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Vegetation LK2

• SWIR (1.3 3.0mm) - incident energy is absorbed
  or reflected, little is transmitted.
• Water absorption bands in this range

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Soil LK2

• Considerably 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.

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Short wave ir
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Water LK2

• Most 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

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Water Longer l visible and near IR absorbed,
reflectance of blue or blue-green
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Water and vegetation may reflect somewhat
similarly in the visible wavelengths but are
almostalways separable in the infrared.
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Short wave ir
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Landsat Bands
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• The spectral response for inorganic materials is
  distinct from vegetation types.

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• Gradual rise in reflectance with increasing
  wavelengths.
• Concrete, light-colored and bright, has higher
  refl than dark asphalt.

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• 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)
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Sensors operating in green, red, and near IR
candiscriminate absorption and reflectance of
vegetation.
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• Absorption in red blue by chlorophyll pigments.
• Reflectance concentrated in the green.
• Thus, most vegetation has a green-leafy color.

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• 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

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Near Infrared Composite (4,3,2) 

• Adding near infrared (NIR) band, drop visible
  blue band

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Landsat Bands
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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.

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• 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.

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• 4 spectral curves
• Variations in depths of absorption bands.
  
  

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• 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.

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Some crops distinguishable by separations in 0.56
to 0.66 µm interval.
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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.
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• 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.

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Which region of the spectrum shows the greatest
reflectance for grasslands pinewoods red
sand silty water
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Spectral Signatures of 4 Materials
Band 1 0.55 um
Band 2 0.85 um
Vis 0.4. 0.7 mm NIR 0.7 1.3 mm SWIR 1.3 3.0
mm
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• 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.

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• 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.

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Spectral Signatures of 4 Materials
Band 1 0.55 um
Band 2 0.85 um
Vis 0.4. 0.7 mm NIR 0.7 1.3 mm SWIR 1.3 3.0
mm
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