Spectral Properties of Vegetation

What is the equation where EMR interacts with the Earth’s surface

Reflection, absorption and transmission vary with the spectral and structural properties of the object it interacts with

What is spectral reflectance

The reflectance within a specified wavelength range (e.g. 0.3-0.4um)

What is a spectral signature

The unique pattern of electromagnetic radiation reflected, absorbed, transmitted, or emitted by a material across different wavelengths

What are the direct interests for studying the interaction between EMR and vegetation

-Often the first surface encountered by the energy used for RS

-Vegetation plays a key role in the carbon cycle

-Helps analyse disease, precision agriculture, forestry, climate change and biodiversity

What are the indirect interests for studying the interaction between EMR and vegetation

Analysing geologic and pedologic patterns

How much of Earth’s land surface is covered by vegetation

70% (with perennial or seasonal photosynthetic activity)

What is the equation for photosynthesis

Carbon Dioxide + water → glucose + oxygen

6CO2 + 6H2O + sunlight → C6H12O6 + 6O2

How do leaves process absorbed light for photosynthesis

Via chlorophylls, which appear green, and carotenoids, which range in color from yellow to orange. These pigments are embedded in the membranes of chloroplasts.

Absorption of light begins when photons strike a pigment molecule, exciting an electron and enabling energy transfer between adjacent pigments. This energy reaching reaction centres where it is transformed into energy-rich molecules

What four main pigments do vegetation contain

-Chlorophyll-a

-Chlorophyll-b

-Xanthophylls

-β-carotene

Where in the leaf interacts with the NIR wavelength

-Occurs at the upper half of the leaf and more importantly between cell and air spaces (amount of airspace increases with level of leaf maturity)

-High reflectance

Does dense vegetation have a higher red wavelength or NIR reflectance

Areas of dense vegetation have lower reflectance in the red waveband but higher in the NIR

What is the red edge

The sharp, sudden increase in plant leaf reflectance between 680 nm and 750 nm, transitioning from heavy red light absorption to high near-infrared scattering

What is the red edge position

The point of maximum slope of the curve in red/near infrared region. It’s sensitive to the chlorophyll content of vegetation

What are the interactions affecting shortwave infrared wavelengths

-Atmosphere and materials on surface contain water

-Amount of reflectance is inversely proportional to water content

-Dominated by water absorption

What other factors affect spectral reflectance of vegetation

-Soil background (i.e. beneath the canopy)

-Solar (illumination) and sensor (viewing) geometry

-Vegetation 3D structure (height, size & shape of leaves, shape of the crown etc)

-Phenology (lifecycle of plants (or animals)). Including temporal characteristics of vegetation growth and depending on available water via rainfall/irrigation, temperature and vegetation type (evergreen vs. deciduous)