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EMR Interaction with ATM &
Earth Surface
ADEA 2324
REMOTE SENSING &AERIAL PHOTO
Dr. Nisfariza Mohd Noor
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Effect of the Atmosphere
EMR is used in RS.
Remember when EMR (sun) illuminates, it has
to travel through Earths atm, some radiation isabsorbed and scattered in the atm.
Particles and gases in the atmosphere canaffect the incoming light and radiation. These
effects are caused by the mechanisms of
scattering and absorption.
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Effects of Atmosphere
Incidence Radiation Scattering & Absorption
Atmosphere
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Scattering
Scattering
when particles or large gas molecules present
in the atm, interaction caused the EMR to be
redirected from its original path.
How much scattering? Depends on severalfactors including the wavelength of the
radiation, the abundance of particles or gases,
and the distance the radiation travels through
the atmosphere.
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1) Rayleigh Scattering
When - particles are very small compared to
the wavelength of the radiation. These could
be particles such as small specks of dust or
nitrogen and oxygen molecules.
Causes shorter wavelengths (UV) of energy
to be scattered much more than longerwavelengths. Rayleigh scattering is the
dominant scattering mechanism in the upper
atmosphere.
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Example of Rayleigh Scattering
Sky appears "blue" during the day. As sunlightpasses through the atmosphere, the shorter
wavelengths (i.e. blue) of the visible spectrum
are scattered more than the other (longer)
visible wavelengths.
At sunrise and sunset the light has to travel
farther through the atmosphere than at middayand the scattering of the shorter wavelengths is
more complete; this leaves a greater proportion
of the longer wavelengths to penetrate the
atmosphere.
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2) Mie Scattering
When particles about the same size as the
wavelength of the radiation. Dust, pollen, smoke
and water vapor are common causes of Mie
scattering which tends to affect longerwavelengths than those affected by Rayleigh
scattering.
Mie scattering occurs mostly in the lower
portions of the atmosphere where larger
particles are more abundant, and dominates
when cloud conditions are overcast.
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3) Non Selective Scattering
When - the particles are much larger than the
wavelength of the radiation. Water droplets and
large dust particles can cause this type of
scattering. Nonselective scattering gets its name from the
fact that all wavelengths are scattered about
equally. This type of scattering causes fog and
clouds to appear white to our eyes becauseblue, green, and red light are all scattered in
approximately equal quantities (blue+green+red
light = white light).
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Absorption
Absorption is the other main mechanism at
work when electromagnetic radiationinteracts with the atmosphere. In contrast to
scattering, this phenomenon causes
molecules in the atmosphere to absorb
energy at various wavelengths.
Ozone, carbon dioxide, and water vapor are
the three main atmospheric constituents
which absorb radiation.
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Target Interactions
Radiation that is not absorbed or scattered in the
atmosphere can reach and interact with the Earth's
surface.
There are three (3) forms of interaction that can take
place when energy strikes, or is incident (I) upon the
surface. These are: absorption (A); transmission (T);
and reflection (R). The total incident energy will
interact with the surface in one or more of these
three ways. The proportions of each will depend onthe wavelength of the energy and the material and
condition of the feature.
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EMR Interaction with the Earth
Radiation - not absorbed / scattered in the atm
can reach and interact with the Earth's
surface.
Three forms of interaction that can take place
when energy strikes, or is incident (I) upon
the surface; absorption (A); transmission(T); and reflection (R).
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Reflection
Reflect ion (R) when radiation "bounces" off the target andis redirected.
In RS, most interested in measuring theradiation reflected from targets. Two types
of reflection : (1) specular reflection and (2)
diffuse reflection
reflected light is what we know as colour;
(example) chlorophyll in plants reflects
green light.
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Transmission
Transmiss ion
occurs when radiation passes through a target
(energy propagates through a medium , what is
not absorbed or ref lected wi l l be transmit ted)
(example) an u ltraviolet f i l ter on a camera absorb s
UV rays but al lows the remaining energy to
expose the fi lm (visi ble EMR).
Changes in densi ty of medium can also slow the
veloc i ty resul t ing in refract ion such as l ight
through a pr ism
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Target Interactions
I= tenaga insiden
R= tenaga yang dipantulkan
A= tenaga yang diserapkan
T= tenaga yang ditransmisikan
= kesemua komponen tenaga adalah fungsi panjang gelombang
I() = R() + A() + T()
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Target Interactions
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Specular Reflection
When a surface is smooth
we get specular or mirror-
like reflection where all (or
almost all) of the energy isdirected away from the
surface in a single
direction.
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Diffuse Reflectance
Diffuse reflection occurswhen the surface is rough
and the energy is reflected
almost uniformly in all
directions.
Most earth surface features lie somewhere
between perfectly specular or perfectlydiffuse reflectors.
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Specular & Diffuse Reflectance
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