Electromagnetic Interactions

Define spectral reflectance:

The reflectance of a surface within a specified wavelength range.

What factors can affect spectral reflectance?

Spectral reflectance can be affected by material type, whether the surface is smooth (specular) or rough (diffuse), and the wavelength range.

Give the word equation for photosynthesis:

Carbon dioxide + water → glucose + oxygen

What are the 4 main vegetation pigments?

• Chlorophyll-a

• Chlorophyll-b

• Xanthophylls

• Beta carotene

Describe the interaction of NIR with vegetation:

• Occurs in the upper half of the leaf, in the spaces between cells

• Airspace increases with maturity

• Hence NIR scans can show vegetation age

Define the red edge:

• A sharp increase in reflectance in the red/NIR region

• Sensitive to chlorophyll content of vegetation

What does a shift of the red edge, towards shorter wavelengths, indicate?

A shift of the red edge towards shorter wavelengths indicates a decrease in chlorophyll and/or water content, suggesting stress.

How does SWIR reflectance indicate water content?

Reflectance of SWIR is inversely proportional to water content.

Where are the 3 main water absorption bands of SWIR?

1.4, 1.9, and 2.7 micrometres

What are some other key factors affecting the spectral reflectance of vegetation?

• Soil background

• Solar and sensing geometry

• Vegetation 3D structure

• Phenology (life cycle of plants)