Spectral Signatures Flashcards
a photon(energy/light) can only be:
- absorbed
- transmitted
- reflected
Spectral Signatures
- A spectral signature is the pattern of spectral response of a material
o Typically visualized with a graph
o Showing the percentage of radiation of different wavelengths reflected from an object - By plotting spectral signatures of different materials together:
o The portions of the spectrum where their signatures differ can be readily identified
by understanding how much much soil,green vegetation and water reflects/wave lenght
the satelites can identify what they see as soil,green vegetation or water
Spectral Signatures
- When we use more than two wavelengths, the plots in multi-dimensional space tend to show more separation among the materials.
- This improved ability to distinguish materials due to extra wavelengths is the basis for multispectral remote sensing
Graph/spectrual signature
Which region of the spectrum
(wavelength) shows the greatest
reflectance for:
a) grasslands? 0.75 microns(18%)
b) pinewoods?0.82 microns(21%)
c) red sand?0.59 microns(69%)
d) silty water?0.54 microns(10%)
if the reflection is too similar it can make it difficult to differentiate the material from each other(ex:grassland and pane wood)
but it is easy differetiate silty water from red sand
Dominant Factors Controlling Leaf
Reflectance
Water
absorption bands:
0.97 μm
1.19 μm
1.45 μm
1.94 μm
2.70 μm
alisade parenchyma mesophyll cells
cells in a leaf
- are the first in contact with the light
- looks like sausegues and are packed together
* Chlorophyll pigments in the Palisade parenchyma mesophyll cells
have a significant impact on the absorption and reflectance of visible
light
- strobly aboserve red and blue light=reflect green light
- cholophyl = green leafs
- as leafs became less healthy/die the chlorophyl deminish, the green starts to faid and other pigments that were less potent then chlorophyl/green(like carotenes, phycocyanin and other ) start to appear more like red and yellow
Chlorophyll
- Chlorophyll a peak absorption is at 0.43 and 0.66 m.
- Chlorophyll b peak absorption is at 0.45 and 0.65 m.
- Optimum chlorophyll absorption windows: 0.45 - 0.52 m and 0.63 - 0.69 m
leafs appear green because chlophyll absorves blue and red lights! (important)
Spongy parenchyma mesophyll cells
- second/last cells with contact with light
- have space between them
- have a significant i**mpact **on the
absorption & reflectance of NIR incident energy.
Dominant Factors Controlling NIR
Reflectance
NIR energy interaction within
the Spongy Mesophyll cells:
- In a typical healthy green leaf, the near-infrared reflectance increases
dramatically between 700 – 1200nm (…Similarly, NIR absorption decreases). - In the NIR, healthy vegetation is normally characterized by
o High reflectance (40 – 60%),
o High transmittance to underlying leaves (40 – 60%),
o Relatively low absorption (5 – 10%). - High diffuse reflectance of the NIR (700 – 1200nm) energy from plant leaves is due to internal scattering at the cell wall-air interface.
Dominant Factors Controlling NIR
Reflectance
- The main reasons that leaves reflect so much NIR energy are:
oThe leaf already reflects 40 – 60% of the incident NIR energy from
the spongy mesophyll, and …
oThe remaining 45 – 50% of the energy penetrates (i.e.
transmitted) through the leaf and can be reflected once again by
leaves below it.
it is bounce around in the space betwen the spongy mesophil
Dominant Factors Controlling MIR / SWIR
Reflectance
- Water vapour in the atmosphere
creates five major absorption bands
across the NIR to middle-infrared (MIR)
wavelengths.
o 0.97, 1.19, 1.45, 1.94, and 2.7m
- Likewise, water content in leaves creates water absorption bands at similar wavelengths
- There is also a** strong relationship between the reflectance in the MIR region from 1.3 – 2.5m …and the amount of water present in leaves.**
- Water in leaves absorb incident energy between the absorption bands with increasing strength at longer wavelengths.
- longer wavelenghts = will absorve more mid enferet energy
- Water is a good absorber of MIR energy, so the greater the
water content of the leaves, the lower the MIR reflectance.
o Conversely, …as the amount of plant water in intercellular spaces
decreases, this causes greater MIR leaf reflectance
Dominant Factors Controlling Leaf
Reflectance
SUMMARY:
The dominant factors controlling leaf reflectance are…
- 0.4 – 0.75m: the various leaf pigments in the palisade parenchyma (e.g. chlorophyll a & b, and -carotene).
- 0.75 – 1.35m: the scattering (i.e. repeated reflectance and
transmission) of near infrared (NIR) energy in the spongy mesophyll, and - 1.35 – 2.8m: the amount of water in the plant.
Basis of Vegetation Indices/index
- Infrared/Red Ratio Vegetation Index
2.
- Infrared/Red Ratio Vegetation Index
- The near-infrared (NIR) to red simple ratio (SR) is the first true vegetation
index: - It takes advantage of the inverse relationship between chlorophyll absorption of red radiant energy and increased reflectance of near-infrared energy for healthy plant canopies.
* Not STANDERLIZED
higher number = healthier vegetation
lower numebers = unhealthy vegetation
