spectral characteristics of water

2. 1. Introduction
2. Electromagnetic radiation
3. Electromagnetic energy interaction.
4. Electromagnetic response of water as function of
wavelength
5. Spectral reflection of water
6. Interaction of visible and near –IR wavelength with water
 Non-organic silts and clay
 Tannin sediments
 Chlorophyll
7. Conclusion
8. Reference

3. Water is transparent and nearly colorless chemical substance
that main constituent of Earth’s streams, lakes, ocean, river,
pounds, reservoirs etc.
1. Water covers 71% of Earth’s surface. It is vital for all known
form of life, on Earth 96.5% of the planet’s curst water is
found in sea’s and ocean, 1.7% in ground water, 1.7% in
glaciers and ice cap on Antarctica.
2. Only about 0.02% of the earth’s water is found in fresh
water stream rivers lakes and reservoirs etc.

4. It chemical formula is H2O meaning that its molecule
continuous one oxygen and two hydrogen atoms that
connected by covalent bonds.

5. Electromagnetic radiation (EM radiation or EMR ) refers to the
waves (or their quanta, photons) of the electromagnetic field,
propagating (radiating) through space carrying electromagnetic
radiant energy such as sun rays. It includes radio waves
microwaves, infrared (visible) light, ultraviolet, X and gamma rays.

6. Electromagnetic waves that originate on the sun are
radiated through space and eventually enter the Earth’s
atmosphere. In the atmosphere radiation interacts with
atmosphere particles which can absorb, scatter or reflect
it back into space.
Much of the suns high energy radiation is absorbed
by the atmosphere preventing it form reaching the
Earth’s surface. This absorption of energy in the upper
atmosphere is an important factor in allowing life to
flourish on the Earth. Atmosphere particles such as
dust, sea salt, ash, water vapor, and water droplets will
reflect energy back into space.

8.  Visible light can be scattered by particles in the
atmosphere allowing only selected wave length to
penetrated to the surface.
 A portion of the energy is able to penetrated the
atmosphere, allowing it to reach the Earth’s surface.
 Radiation that is able to penetrated the material and pass
through it is said to be transmitted.
 Most wavelength of visible light energy from the sun are
transmitted through atmosphere allowing it to come into
contact with the Earth’s surface as water surface.
 One’s this radiation reaches the surface, it interacts with
the surface materials where it can be reflected back into
space or a absorbed and red- emitted as thermal infrared
energy.

9. 1. Water (in soil, vegetation or water bodies) absorbs
radiation at near-IR wavelengths and beyond ( strong
absorption bands at about 1.4, 1.9 and 2.7 µm.
2. Absorption and scattering of light in pure water relatively
little energy with wavelength <0.6um resulting in high
transmittance in the blue green portion of the spectrum.

11. 3. Molecular water absorption dominant in ultraviolet
(<400nm) and in the yellow through the near-
infrared portion of the spectrum (>580nm).
4. Almost all incident near- infrared and middle-
infrared (740-2500nm) radiant flux entering a pure
water body is absorbed with negligible scattering
taking place.
5. This is why water is so dark on black and white
infrared or color – infrared film.
6. Scattering with water column is especially important
in the violet, dark, blue and light blue portions of the
spectrum (400-500nm).
7. This reason water appears blue to our eyes.

12. Wavelength(nm) Absorption a Scattering b Total
attenuation c
250 -ultraviolet 0.190 0.032 0.2200
300 -ultraviolet 0.040 0.015 0.0550
320 -ultraviolet 0.0200 0.00082 0.0320
350 -ultraviolet 0.012 0.0082 0.0202
400 -violet 0.006 0.0048 0.0108
420-violet 0.005 0.00401 0.0090
440-viloet 0.004 0.0032 0.0012
460-dark blue 0.002 0.0027 0.0047
480- dark blue 0.003 0.0022 0.0052

13. 500-light blue 0.006 0.0019 0.0079
520- green 0.0014 0.0016 0.0156
540- green 0.029 0.0014 0.304
560-green 0.039 0.0012 0.402
580-yellow 0.074 0.0011 0.0751
600- orange 0.20 0.00093 0.2009
620- orange 0.24 0.0082 0.2408
640- red 0.27 0.00072 0.2707
660- red 0.310 0.00064 0.3106
680- red 0.38 0.000056 0.3806
700- red 0.60 0.0005 0.6005
740- near-infrared 2.25 0.0004 2.2504
760- near-infrared 2.56 0.00035 2.5604
800-near-infrared 2.02 0.00029 2.0203

14. Reflection from a water body can stem for and interaction
with :-
1. The water surface (specular reflection).
2. With material suspended in the water, or
3. With bottom of the water bodies.

15. 1. The majority of the radiant flux incident upon water is
not reflected but is either absorbed or transmitted.
2. At visible wavelength (0.4 to 0.7 µ m) of EM little energy
is absorbed, a small amount usually under 5% is reflected
and the majority is transmitted.
3. Water absorbed strongly at near – infrared wavelength ,
leaving little radiation to be either reflected or
transmitted.

17. 4. Although water surface may be more homogeneous
than soil surface we can still expect some variability
in the reflectance of a body of water.
5. The most important factors are the depth of water
and material within the water.
6. In shallow water some of the radiation is reflected
not by the water itself but from the bottom of the
water body.
7. The three most common materials suspended in the
water are none organic sediments, tannin, and
chlorophyll.

18.  None organic silts and clays increase the reflectance at
visible wavelength due to interaction with scattering by
soil like particles. This cost by the high concentration of
fine ‘rock flour’ sediment suspended in the water.
 In agriculture scenes the main coloring agent is tannin
produced by decomposing humus. This yellowish to
brown color and results in decreased blue and increased
red reflectance.
 Chlorophyll :- content must be very high before changes in
reflectance can be detected water bodies that contain
excessive levels of chlorophyll have reflections properties
that resemble at least in part , those of vegetation with
increased green and decreased blue and red reflectance.

20. A significant amount of spectral characteristics of water
has taken placed to develop remote sensing methods that
can obtain quantitive , spatial measurements of these
important hydro logic variables.
Spectral characteristic of water in remote sensing can be
used to inventory and monitor the spatial extent, organic/
inorganic constituents , depth, chlorophyll, substance,
phytoplankton of water in rivers lakes reservoirs, seas and
ocean’s.

21. 1. Remote sensing of the Environment (Jhon
R. Jensen)
2. Wikipedia, Fundamental of Remote
Sensing (Joseph George 2003)