1. EMR:INTRACTION WITH
ATMOSPHERE

2.  Remote sensing is the science of acquiring
information about the Earth's surface without
actually being in contact with it.
• Remote sensing is the observation and
measurement of objects from a
distance, i.e. instruments or recorders are
not in direct contact with objects under
investigation.
What is Remote Sensing?

3. How Remote Sensing Works
What is Remote Sensing?

4. Energy recorded by remote sensing systems undergoes
fundamental interactions that should be understood to
properly interpret the remotely sensed data.
For example, if the energy being remotely sensed comes from
the Sun, the energy:
• is radiated by atomic particles at the source (the Sun),
• propagates through the vacuum of space at the speed of
light,
• interacts with the Earth's atmosphere,
• interacts with the Earth's surface,
• interacts with the Earth's atmosphere once again, and
• finally reaches the remote sensor where it interacts with
various optical systems, filters, emulsions, or detectors.
ELECTRO MAGNETIC RADIATION

5. Electromagnetic Radiation
An electrical field (E)
A magnetic field (M) oriented at right angles to the
electrical field.
Energy Source or Illumination (A)

6. A body surface can
1. absorb incident radiation,
2. reflect incident radiation,
a) as a mirror
b) with spherical symmetry (Lambert)
3. transmit incident radiation,
4. emit radiation.
The characteristics are a function of the
wavelength of the radiation.
LAW OF EMR

7. Wavelength
The wavelength is the length of one wave cycle
Electromagnetic Radiation

8. Color Wavelength (nm)
Red 780 - 622
Orange 622 - 597
Yellow 597 - 577
Green 577 - 492
Blue 492 - 455
Violet 455 - 390
Electromagnetic Radiation

9. Frequency
Frequency refers to the number of cycles of a
wave passing a fixed point per unit of time.

10. Radiation and the Atmosphere
The energy travels from its source to the target, it will come in contact with &
interact with the atmosphere it passes through. This interaction may take place a
second time as the energy travels from the target to the sensor. All these interaction
occurred by the following ways-
 Interaction with the atmosphere:
• Scattering
• Absorption.
 Interaction with target/surface:
• Absorption.
• Transmission.
• Reflection. Fig: Interaction with the Atmosphere
. Fig: Interaction with the Atmosphere

11. Before radiation used for
remote sensing reaches the
Earth's surface it has to travel
through some distance of the
Earth's atmosphere. Particles
and gases in the atmosphere
can affect the incoming light
and radiation. These effects
are caused by the
mechanisms of
Scattering
Absorption.
EMR: Interaction with the Atmosphere

12. Radiation-Target
Absorption
Transmission
Reflection
Interaction with
the Target (C)
Absorption (A)
Transmission (T)
Reflection (R)
Reflectance

13. Scattering
Scattering occurs when particles or large gas molecules present
in the atmosphere interact with and cause the electromagnetic
radiation to be redirected from its original path.
How much scattering takes place depends on several factors
including the wavelength of the radiation, the abundance of
particles or gases, and the distance the radiation travels through
the atmosphere. There are three (3) types of scattering which take
place
1.Rayleigh Scattering.
2.Mie Scattering.
3.Non-selective Scattering.

15. Mie Scattering
Mie scattering occurs when the particles are just 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 longer wavelengths 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.
Non-selective Scattering
 This occurs 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 because
blue, green, and red light are all scattered in approximately equal quantities
(blue+green+red light = white light).
The final scattering mechanism of importance is called Non-selective scattering.
This occurs when the particles are much larger than the wavelength of the radiation.
Water droplets & large dust particle can cause this type of scattering. This type of
scattering causes fog& clouds to appear white to our eyes.

16. At sunset, solar radiation must
traverse a longer path through the
atmosphere. Viewing a setting sun, the
energy reaching the observer is largely
depleted of blue radiation, leaving
mostly red wavelengths (Rayleigh).
Dust/smoke adds additional scattering
with a wavelength dependence that
increases the red sky effect (Mie).
RED SKY AT NIGHT

17. Absorption
Absorption is the other main mechanism at work when
electromagnetic radiation interacts 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.
Ozone serves to absorb the harmful (to most living things)
ultraviolet radiation from the sun. Without this protective layer in
the atmosphere our skin would burn when exposed to sunlight.
You may have heard carbon dioxide referred to as a greenhouse
gas. This is because it tends to absorb radiation strongly in the far
infrared portion of the spectrum - that area associated with
thermal heating - which serves to trap this heat inside the
atmosphere.

19. Absorption of EMR by atmosphere
Different molecules absorb different wavelengths of
radiation:
• O2 and O3 absorb almost all wavelengths shorter than
300 nm.
• Water (H2O) absorbs many wavelengths above 700 nm,
but this depends on the amount of water vapor in the
atmosphere.
When a molecule absorbs a photon, it increases the
energy of the molecule. We can think of this as heating
the atmosphere, but the atmosphere also cools by
emitting radiation.

20. Electromagnetic Radiation & Health
Electromagnetic radiation can be classified into two types: ionizing radiation and
non-ionizing radiation, based on its capability of ionizing atoms and breaking
chemical bonds. Ultraviolet and higher frequencies, such as X-rays or gamma rays
are ionizing, and these pose their own special hazards: see radiation and radiation
poisoning. Non-ionizing radiation, discussed here, is associated with electrical and
biological hazards.
 Electrical Hazard.
 Fire Hazard.
 Biological Hazard.
In many respects, remote sensing can be thought of as a reading process.
Using various sensors, we remotely collect date that may be analyzed to
obtain information about the objects, areas or phenomena being
investigated. In most cases the sensors are electromagnetic sensors either
airborne or space borne for inventorying.