Spectral Signatures and Their Interpretation GEOG3610 Remote Sensing and Image Interpretation Spectral Signatures and Their Interpretation Spectral Signatures and Their Interpretation

Spectral Signatures and Their Interpretation GEOG3610 Remote Sensing and Image Interpretation Spectral Signatures and Their Interpretation EMR and earth materials interaction Spectra of earth materials Multispectral images and their interpretation Spectral Signatures and Their Interpretation

EMR and earth materials interaction GEOG3610 Remote Sensing and Image Interpretation EMR and earth materials interaction When EMR from the sun reaches the earth surface, it is transmitted - transmittance absorbed - absorbance reflected - reflectance The nature of how the earth materials transmit, absorb or reflect the solar EMR is called spectral signature of an object. Spectral Signatures and Their Interpretation

Spectra of earth materials GEOG3610 Remote Sensing and Image Interpretation Spectra of earth materials Vegetation Soil and rocks Water, ice and snow Cloud, fire and smoke Spectral Signatures and Their Interpretation

GEOG3610 Remote Sensing and Image Interpretation Vegetation Contains water, cellulose (tissues and fibres), lignin (non-carbohydrate constituent of wood), nitrogen, chlorophyll (“green” pigments) and anthocyanin (water-soluble pigments). Depending on how ‘active’ (i.e. kinds of chlorophyll) a green vegetation is, the combination of transmittance, absorbance and reflectance vary in different bands of the spectrum. Spectral Signatures and Their Interpretation

Physiological factors GEOG3610 Remote Sensing and Image Interpretation Physiological factors Leaf structure Reflectance, transmittance, and absorptance spectra Leaf maturation Mesophyll arrangements (internal structural differences) Spectral Signatures and Their Interpretation

GEOG3610 Remote Sensing and Image Interpretation Leaf structure A leaf’s structure and its reflectance characteristics at visible and near IR wavelengths. Spectral Signatures and Their Interpretation

Transmittance, absorbance and reflectance GEOG3610 Remote Sensing and Image Interpretation Transmittance, absorbance and reflectance Fractions of the total light incident on the upper surface of a mature orange leaf that is reflected, absorbed and transmitted. Spectral Signatures and Their Interpretation

GEOG3610 Remote Sensing and Image Interpretation Absorption spectra Absorption spectra of chlorophyll a (blue-green) and chlorophyll b (yellow-green). Spectral Signatures and Their Interpretation

GEOG3610 Remote Sensing and Image Interpretation Spectral reflectance Average spectral-response curves for six materials. Spectral Signatures and Their Interpretation

Spectral reflectance (cont.) GEOG3610 Remote Sensing and Image Interpretation Spectral reflectance (cont.) Below: Average spectral-response curves for four types of vegetation Right: Average spectral-response curves for a plant leaf as it progresses from a healthy state through different stages of damage. Spectral Signatures and Their Interpretation

GEOG3610 Remote Sensing and Image Interpretation Other factors Leaf damage; Sun and shaded leaves; Leaf water content; Leaf air spaces; and Salinity and nutrient levels. Spectral Signatures and Their Interpretation

GEOG3610 Remote Sensing and Image Interpretation Vegetation canopy Transmittance of leaves; Amount and arrangement of leaves; Characteristics of, e.g., stalks, trunks, limbs, etc.; Background (soil, leave litter, etc.); Solar zenith angle; Look angle; and Azimuth angle. Spectral Signatures and Their Interpretation

GEOG3610 Remote Sensing and Image Interpretation Soil and rocks The reflectance from soil and rocks is influenced by: colour mineral contents (chemical composition or crystalline structure) structure and others We use soil for discussion Spectral Signatures and Their Interpretation

Field reflectance spectra GEOG3610 Remote Sensing and Image Interpretation Field reflectance spectra packed ploughed Field reflectance spectra of green grass, dead grass, Virginia Pine, Scarlet Oak, packed bare soil and ploughed soil with cobbles. Spectral Signatures and Their Interpretation

Factors influencing interpretation of soils GEOG3610 Remote Sensing and Image Interpretation Factors influencing interpretation of soils Soil colour Mineral content - depends upon the intermolecular vibration of the molecules Organic matter - influences soil colour and moisture Particle size - reflectance and thermal diffusivity, and moisture. Spectral Signatures and Their Interpretation

Reflectance of minerals GEOG3610 Remote Sensing and Image Interpretation Reflectance of minerals Directional hemispherical reflectance spectra in the 0.4-2.5m wavelength region and biconical reflectance spectra in the 2-25m wavelength region of two clay minerals: kaolinite and montmorillonite. Spectral Signatures and Their Interpretation

Factors influencing interpretation of soils (cont.) GEOG3610 Remote Sensing and Image Interpretation Factors influencing interpretation of soils (cont.) Soil texture - mainly indirect effects on, e.g., soil moisture. Structure and surface roughness (soil aggregation) - "smoothness" of soil - have significant effects on RADAR response. Soil emissivity - thermal emissivity: ratio of energy radiated at the surface / black body Soil temperature - influences the interpretation of thermal imagery and time of sensing. Spectral Signatures and Their Interpretation

Reflectance from soils GEOG3610 Remote Sensing and Image Interpretation Reflectance from soils O2 and CO2 and water vapour absorption; Sun illumination varies with atmospheric conditions and solar radiation Effects of soil structure, surface roughness, etc. The intensity of the sun peaks at about 0.5m falling off rapidly at shorter and longer wavelengths. Spectral Signatures and Their Interpretation

GEOG3610 Remote Sensing and Image Interpretation Water, ice and snow Water visible transmittance is high high absorptance in NIR influenced by the cleanness Snow high reflectance in < 1.5m low at 1.5 and 2m very low in the thermal IR Spectral Signatures and Their Interpretation

Reflectance of ocean water GEOG3610 Remote Sensing and Image Interpretation Reflectance of ocean water Calculated change in bulk reflectance of ocean water with increasing concentration of phytoplankton. Spectral Signatures and Their Interpretation

GEOG3610 Remote Sensing and Image Interpretation Reflectance of snow Frost Fine Coarse Computed reflectance spectra of three different textures of snow (coarse, fine, and frost) for (a) the 0.3-3.0m wavelength region, (b) the 3-14m wavelength region. b Fine Frost Coarse Spectral Signatures and Their Interpretation

GEOG3610 Remote Sensing and Image Interpretation Cloud, fire and smoke Cloud strong reflectance in visible and NIR associated with shadow can be penetrated by radar Fire high temperature Wien’s displacement law Smoke highly visible (black or white) in visible can be penetrated by TM5 and TM7 as their wavelength is larger than the most smoke particles. W = 2,897m K Spectral Signatures and Their Interpretation

Detecting smoke and fires TM band 1-5 and 7 show file smoke (band 1-4) and location of the fire (band 5, 7).

Multispectral images and their interpretation GEOG3610 Remote Sensing and Image Interpretation Multispectral images and their interpretation Single image band interpretation similar to airphoto interpretation beware of the spectral wavelength of the band and the spectral signatures of the objects Colour composites Multispectral band statistics Multispectral classifications Spectral Signatures and Their Interpretation

Panchromatic and infrared photographs GEOG3610 Remote Sensing and Image Interpretation Panchromatic and infrared photographs Panchromatic (left) and infrared (bottom) photographs of the Goldach region, Switzerland. Note the clear separation of tree types and the differentiation between the small stream and its terrain background in the infrared photograph. Spectral Signatures and Their Interpretation

Infrared and panchromatic photographs GEOG3610 Remote Sensing and Image Interpretation Infrared and panchromatic photographs Infrared Panchromatic (A) channel bar accretion - darker-toned areas represent the most recent deposits (moist) that have not yet been vegetated, (B) minor channel through a channel-bar complex, (C) meander cutoff, (D) back swamp, and (E) point-bar swamp. Spectral Signatures and Their Interpretation

Single band interpretation GEOG3610 Remote Sensing and Image Interpretation Single band interpretation TM1 TM2 TM3 TM4 TM5 TM7 Spectral Signatures and Their Interpretation

GEOG3610 Remote Sensing and Image Interpretation Colour composites Number of composites Example: TM 6 non-thermal bands Spectral Signatures and Their Interpretation

Colour Infrared photos GEOG3610 Remote Sensing and Image Interpretation Colour Infrared photos Spectral Signatures and Their Interpretation

Colour composites (cont.) GEOG3610 Remote Sensing and Image Interpretation Colour composites (cont.) Spectral Signatures and Their Interpretation

Colour composites (cont.) GEOG3610 Remote Sensing and Image Interpretation Colour composites (cont.) TM 1 2 3 TM 2 3 4 TM 1 4 5 Spectral Signatures and Their Interpretation

Object signatures on panchromatic and infrared photographs GEOG3610 Remote Sensing and Image Interpretation Object signatures on panchromatic and infrared photographs Spectral Signatures and Their Interpretation

Multispectral band statistics GEOG3610 Remote Sensing and Image Interpretation Multispectral band statistics Histogram Spectral Signatures and Their Interpretation

Multispectral band statistics (cont.) GEOG3610 Remote Sensing and Image Interpretation Multispectral band statistics (cont.) Scattergram Spectral Signatures and Their Interpretation

GEOG3610 Remote Sensing and Image Interpretation Summary Different earth’s materials have various characteristics in reflecting solar EMR. The reflectance pattern of an object is called its spectral signature. Understanding spectral signatures of earth’s materials is essential for remote sensing image interpretation. The ultimate goal is to guide spectral band selection and create human colour vision for proper image interpretation. Spectral Signatures and Their Interpretation