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

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

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

11. 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

12. 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

13. 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

14. 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

15. 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

16. 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

17. Reflectance of minerals
GEOG3610 Remote Sensing and Image Interpretation
Reflectance of minerals
Directional hemispherical reflectance spectra in the 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

18. 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

19. 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

20. 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

21. 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

22. 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 m wavelength region, (b) the 3-14m wavelength region. b
Fine
Frost
Coarse
Spectral Signatures and Their Interpretation

23. 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

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

25. 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

26. 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

27. 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

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

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

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

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

32. 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

33. 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

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

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

36. 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