Vegetation Flashcards
What are the spectral curves of different material dependent upon?
- Reflection, Absorption, and Transmittance of their constituents
What is a general guide for image processes?
- DN
- Calibration
- Correction
- Reflectance
How many visual cones do humans have?
3 (visible range)
How many visual cones to butterflies have?
5 (Visible, UV and Violet)
- UV spectrum may be used for mating purposes (wings look attractive etc.)
What is the difference between human and butterfly vision?
- Butterflies see more cones and into UV spectrum
- Butterflies have ‘narrower bands’
- Narrow is generally better
Mantis shrimp
- Extraordinary vision
- Approximately 16 visual cones
- Many narrow bands in the visual range
What can knowledge about variations in species and vegetation distribution patterns, vegetation growth cycles, and plant physiology and morphology provide insight into?
- Climatic, geologic, and physiographic characteristics of a region
Total incident irradiation = ?
Total Reflected plus Total Absorbed plus Total Transmitted
- Depending on spectrum, light will be 1 of these 3
How does light reach the understory?
- Transmittance through leaves of canopy
What are the potential fates of EM radiation absorbed by a pigment?
- Usually blue and red absorbed:
- Dissipated as heat
- Emitted in longer wavelength (fluorescence)
- Used for photosynthesis (trigger chemical reaction)
- Depends on amount of energy
What is the general chemical eqn for photosynthesis?
6 Carbon Dioxides plus 6 waters plus light energy (PAR spectra) = Carbohydrate (sugar, c6H12O6) plus 6 Oxygens
What does PAR stand for?
Photosynthetically Active Radiation
What is PAR?
- Spectral range 400 - 700nm that organisms can use for photosynth
Why is the spectral range for PAR the way it is?
- Photons at shorter wavelength too energetic and damage cells and absorbed by atmospheric ozone
- Longer Photons don’t have enough energy to fuel photosynth
Plant cuticle
- 1st layer
- Holds water on surface
- Regulates light
- But doesn’t play much role
Stoma (Stomata)
- Hole on bottom of leaf that releases carbon dioxide
Parenchyma
- 2nd layer
- Holds chlorophyl in chloroplasts
- Absorbs light (red and blue)
- Unabsorbed transmits to spongy mesophyll
Chloroplasts and Granum
- Found in Parenchyma and spongy parenchyma mesophyll
- Where light reaction occurs
- Absorb red and blue light
- Granum (stack of thylakoids) in chloroplast has chlorophyl and pigments, where photosynth begins
What are the 7 main factors that affect leaf optical properties?
- Pigment composition
- Internal and external leaf structure
- Water content
- Age
- Nutrient Stress
- Healthiness
- Background
What is the dominant factor controlling leaf reflectance?
- Leaf pigments in the palisade mesophyll:
- Chlorophyll a and b
- Beta carotene etc.
What wavelengths does chlorophyl a absorb?
0.43 and 0.66
What wavelengths does chlorophyl b absorb?
0.45 and 0.65
What is the overall perception of transmitted wavelengths after chlorophyl a and b has absorbed their corresponding wavelengths?
- Overall green perception
- Lack of absorption in the 0.5 to about 0.6 range
Carotene
- 35 to 0.5 micrometers
- Transmits/reflects orange colour
Phycoerythrin
- 55 micrometers
- Transmits/reflects red with a bit of purple
Phycocyanin
- 6 micrometers
- Transmits/reflects bluish-green (cyan)
Xantophyll
- 35 to 0.5
- Transmits/reflects yellow
What does pigmentation depend on?
- Seasonal senescence
- Environmental stress
What does a green leaf represent? Yellow? Red? Brown?
G = Photosynthesizing, Y = Beginning of senescence R = Late stage senescence B = Fallen, dieing
What happens to the spectral response as a leaf dies?
- Less chlorophyl absorption at 0.43 and0.66 micrometers
- Blue shift of the red edge from just above 700nm to just below 700nm
What are the ranges that indicate stress?
535 - 640nm and 685 - 700nm
Blue shift of the red edge
- Red edge = sharp increase from red to NIR reflectance
- As pigmentation changes the sharp edge shits towards blue range
Can the blue shift be detected on Landsat 7, 8, or Sentinel-2?
Might not be able to see with Sentinel-2 b/c red band is very narrow
- Landsat 8 might be best with a larger red band?
What happens in the spongy mesophyll?
- NIR energy interaction
- High reflectance at 0.7 to 1.4 micrometers b/c of internal scattering at the cell wall-air interfaces within the leaf (high NIR)
- Refractive index (n) - hydrated cells: 1.4
- Intracellular air: n = 1.0003
Healthy mature leaves…?
- Absorb radiation very efficiently in blue and red
- Chlorophyll a = photosynthesis
Why do plants have high reflectance and transmittance in the NIR? i.e. low absorption
- If NIR was absorbed as efficiently as visible plant would be too warm and proteins denatured
- Evolutionary adaptation of spongy mesophyll allow most NIR to reflect or transmit
Why is the scattering in NIR possible and satellite bands important to be in that location?
- Less atmospheric water absorption in those wavelengths/bands
What are the generalized interactions of blue, red, and NIR light with plant tissue of young, mature, and old leaf?
- Young: G and IR reflected, R and B absorbed
- Mature: G reflected, R and B absorbed, More scattering of IR as spongy mesophyll has more air spaces
- Old/senesced: B, R, G, and IR reflected, spongy mesophyll broken down
What is the spectral behaviour of vegetation at the leaf level mostly dependent on?
- Visible range (400 - 700nm): Absorption of chlorophyll a (430 and 660) and chlorophyl b (450 and 650), green colour from chlorophyl not absorbing green light
- NIR (700-1200nm): Cell structure and interstitial air spaces (index of refraction) act to scatter radiation, prevents heat damage
- MIR (1200-2700nm): Plant water content, strong absorption bands at 1450 and 1940nm
MIR
1.3 - 2.5 micrometers
Water conditions: turgid vs. relatively turgid
- Turgid = high water content
- Relatively turgid = low water content
- More water content = more IR absorption
- Less water content = More reflection
Water absorption bands (nm)
- 970
- 1190
- 1450
- 1780
- 1940
- 2700
Why are landsat bands 6 and 7 located where they are?
- Because that is where interactions with MIR and leaf water content occur
- Atmospheric window where wavelengths are not absorbed by atmospheric water
Plant response to parasites
- Change in pigments (visible)
- Necrosis: NIR
- Water content: NIR, SWIR
- Parasites in the intercellular spaces therefore compacts the internal structures, NIR
Plant response to fungus
- Loses chlorophyll pigments (visible)
- Water content, NIR, SWIR
What do insect vectors do?
- Carry fungus from infected to healthy trees
- Fungus blocks the water translocation
What does a mountain pine beetle do?
- Blocks water translocation
Beetle infestation: Endemic
A few trees, isolated
Beetle infestation: Incipient
A stand of trees infected, at least a few dozen
Beetle infestation: Outbreak
Entire stands of forest infected, large areas
Why is there an increase in MIR reflection when a plant is infected with fungus?
- Less water is absorbing in the leaves
Why is remote sensing a good option for monitoring mountain pine beetle infestation?
- Tree can still look fine in visible range
- But early, green, attack stage shows very decreased IR absorbance
- Red attack is late stage and only then can damage bee seen by eye
General vegetation senescence
- NIR begins to decrease
- Red reflection increases b/c no longer absorbing chlorophyll
Advantages of handheld spectral radiometer? Disadvantage?
- Achieve ideal curves
- Separate desiccated mixed with healthy veg
- No atm. involved
- No pixel mixing
- Not as good spatial and spectral resolution
What are possible causes for the blue shift of the red edge?
- Natural senescence
- Water deficiency
- Toxic materials
- Disease
- Decrease chlorophyl a and the red absorption shifts to shorter wavelength and width of absorption band decreases
Vegetation index
- Indicator of relative abundance and activity of green vegetation
- Dimensionless
- Radiometric measures that function as indicators
What does the vegetation index indicate
- Leaf-area index
- Precent green cover
- Chlorophyll content
- Green biomass
Advantages of Vegetation index
- Minimize effects of atmosphere
- Normalize canopy background and topography
LAI
Leaf-Area Index
- Amount of vegetation
- Function of Simple Ratio
Simple Ratio
= NIR/R
- NIR represents vegetation
- R represents soil reflectance and chlorophyll absorption
- Looks at vegetation present and LAI
High LAI (biomass) = what SR?
- High SR, lots of vegetation
- Senesced would be much smaller than healthy veg
Problems with SR
- Unitless w/ no range
- Depends on digital number in image being worked with therefore is image dependent
- Cannot compare output on 2 different scales
- Only usable for 1 image and cannot compare images, especially 8 vs. 16 bit
NDVI
- Normal Distribution Vegetation Index
- Normalized SR into 0 - 1 range
= NIR - R/NIR plus R - Good indicator of a good growing year for healthy veg
- Increase in NDVI = Increased biomass
What is the difference for healthy and unhealthy veg relating to the NDVI
- Healthy absorbs most visible and reflects large portion of NIR, high NDVI
- Unhealthy/sparse reflects more visible and less NIR, low NDVI
Applications of NDVI
- Growing seasons (compare years) health/yield in subsaharan Africa
- Drought in California (compare years)
- Input for global carbon models, LAI APAR percent cover biomass
Problems with NDVI
- Saturation
- Soil colour
- Moisture content
- Atmospheric content
- Atmospheric conditions
- Presence of dead material in canopy
- All the above change regionally and/or seasonally
Why is soil colour a problem for NDVI?
- If soil shows and depending on type (brown vs red-iron rich) gives a different signal
How does presence of dead material affect NDVI?
- NDVI can see a dead branch but cannot detect that it isn’t affecting the plant and that the plant is still healthy
How can problems with the NDVI be fixed?
- Soil adjustments
- Blue band for atmospheric normalization
SARVI
Soil and Atmosphere Resistant Vegetation Index
- Soil calibration factor uses the blue channel
= 2(densityNIR - densityR)/(L plus densityNIR plus C1densityR - C2densityBlue)
Relationship between vegetation and soil during growing season for SR
- Planted, watered moist soil, no veg yet, low red
- Intermetiate biomass/canopy closure less red and more NIR, moves up centre of shark fin graph
- Almost ripe is closer to peak, more NIR, less R
- Ripe/high canopy closure/biomass is peak, high NIR, less R
- Harvested is back to soil line but more R b/c not moist, no longer watered
In false colour, what does results in cyan?
- Green plus red
- Closer to bare soil
Leaf additive reflection
- Leaf reflects 40 - 60 percent incident NIR from spongy mesphyll
- Transmits remaining 45 - 50 percent through to layer below
- Transmitted can then be reflected once again by leaves in lower canopy
- More leaves in the canopy means more NIR reflectance
