l4 interactions atm 27feb2013

7/28/2019 L4 Interactions ATM 27Feb2013

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EMR Interaction with ATM &

Earth Surface

ADEA 2324

REMOTE SENSING &AERIAL PHOTO

Dr. Nisfariza Mohd Noor

[email protected]


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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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end

l4 interactions atm 27feb2013

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