Spectral Properties of Ground Materials

• Module M.SIA.I14M covers GIS and Remote Sensing for Agriculture
• Lecture 6 focuses on spectral properties of ground materials.

Spectral Signature

• When electromagnetic energy interacts with an object, absorption, reflectance, transmittance, or emittance occur due to the object's chemical and structural properties.
• Every object possesses a unique spectral property.
• Reflectance curves are used to explain these spectral properties, showing reflectance as a function of wavelength because reflected energy can be measured.
• The unique spectral curve of a known object defines its spectral signature.

Bare Soil

• The soil's spectral property varies based on factors, including soil color, moisture content, and the presence of carbonates and iron dioxide.
• Organic dominated soil is the variety with the lowest reflectance.
• Iron dominated soil is the variety with the highest reflectance.

Water

• Water generally exhibits lower reflectance.
• It reflects approximately 10% of energy in the visible range, with very little reflectance in the Near-Infrared (NIR) spectrum.
• Beyond the 1.2 µm wavelength, most energy is absorbed by the water.
• Ocean water, turbid water, and water with chlorophyll have differing reflectance.

Snow and Ice

• Show and ice exhibit strong reflection in the visible and NIR.
• Strong absorption occurs at longer wavelengths.
• Grain size and the age of the ice or snow significantly affect reflectance.
• Impurities in snow or ice reduce reflectance.

Spectral Property of Vegetation

• Vegetation's spectral properties depend on multiple factors.
• Leaf orientation, structure of leaf canopy, leaf pigmentation, leaf thickness, cell structure, and water content in the leaves are all important.

Vegetation Spectral Signature

• Leaf pigments have greatest influence over visible light.
• Cell structure has greatest influence over near infared.
• Leaf biochemicals, proteins, lignin, cellulose, and water content influence shortwave infared.
• Visible, near infared, and shortwave infraread are all important spectral features.

Vegetation in Visible Spectrum (400 - 750 nm)

• Chlorophyll a and b absorb energy, especially blue and red, from the visible spectrum.
• Other leaf pigments have different absorption capacities, with xanthophyll absorbing blue, carotenoids absorbing blue at 0.44 and 0.46 µm, and anthocyanins absorbing blue and green.

Vegetation in NIR Spectrum (780-1300 nm)

• The optical properties in the Near-Infrared (NIR) range are primarily influenced by leaf structure.
• Spongy mesophyll cells in the interior of leaves strongly reflect NIR.
• High reflectance in NIR causes vegetation to appear bright.
• Two minor water-related absorption bands are located at 0.97 and 1.2 µm.

Vegetation in Red-Edge (750-780 nm)

• The red-edge marks the transition zone between the red and NIR portions of the spectrum.
• The red region has lower reflectance, while NIR has very high reflectance in the vegetation spectral signature.
• The transition zone between red and NIR shows a very high gradient of reflectance.

Vegetation in SWIR (1300 – 2500 nm)

• Absorption in this range is primarily due to water, cellulose, lignin, and other biochemical constituents.
• Prominent water absorption wavelengths are at 1.40 and 1.94 µm.

Absorption features summary

• Chlorophyll absorbs light with wavelengths 0.43, 0.46, 0.64, 0.66 μm and exhibits electronic transitions.
• Water absorbs light with wavelengths 0.97, 1.20, 1.40, 1.94 μm and exhibits O-H bond stretching.
• Protein and nitrogen absorbs light with wavelengths 1.51, 2.18 μm and exhibits N-H stretching, bending, and C-H stretching.
• Oil absorbs light with wavelength 2.31 μm and exhibits C-H stretching and bending.
• Lignin absorbs light with wavelength 1.69 μm and exhibits C-H stretching.
• Cellulose and sugar absorbs light with wavelength 1.78 μm.

Effect of leaf structure

• Leaf structure greatly affects the infrared.
• Diagrammatic illustration of the radiation fluxes at both 550 nm and 1000 nm.
• Spectral properties of Tussilago farfara L. leaves with hairs.

Effect of Leaf Canopy

• Leaf canopies cause absorption and scattering of the sun's light.

Leaf Area Index (LAI)

• LAI (m²/m²) is geometrically defined as the total one-sided area of photosynthetic tissue per unit of ground surface area.
• LAI helps to derive canopy reflectance.

Lecture on spectral properties of ground materials. It covers spectral signatures, bare soil reflectance based on soil color and moisture, and water reflectance. Every object possesses a unique spectral property.