EMR

1. Stages of Remote Sensing…..
• Interaction between EMR and atmosphere
• Atmospheric windows
• When the sun is present, we can see earth features by virtue of
reflected solar energy.
• The longer wavelength energy emitted by ambient earth features can
be observed only with non photographic sensing system.

2. Energy Interactions in the Atmosphere
Atmospheric Scattering: is the unpredictable diffusion of
radiation by particles in the atmosphere. The redirection of
EM energy by the suspended particles in the air.
dp << l Rayleigh scattering
dp =l Mie scattering
dp >> lNon-selective scattering
Absorption: Atmosphere selectively absorbs energy in
different wavelengths with different intensity.

3. Scattering causes degradation of image quality for
earth observation. At higher altitudes, images acquired in
shorter wavelengths (ultraviolet, blue) contain a large
amount of scattered noise which reduces the contrast of
an image.

4. RAYLEIGH SCATTERING
Rayleigh Scattering (or molecular scattering): occurs when the
effective diameter of the matter (usually air molecules
such as O2 and N2 in the atmosphere) are many times
smaller (usually< 0.1) than the wavelength of the
incident electromagnetic radiation.

5. • The amount of scattering is
inversely proportional to the
fourth power of the
radiation’s wavelength.
• It is equal in fore and back
directions
• The scattering takes place in
the upper 4.5 km of the
atmosphere.

6. Blue sky
Day time
Earth
Atmosphere
B
G
R
Earth
Sunset
Blue
Red
Sun
Sun
Rayleigh Scattering causes blue sky during daytime and red sky at
sunset. In absence of RS sky will be black.
With long path, scatter/absoption of short λ is so complete
that only Less scattered longer λ of orange/red are only visible.

7. Mie scattering (non-molecular scattering): be
essentially spherical particles present with diameters
approximately equal to the size (range 0.1 to 10 times) of
the wavelength of the incident energy.
Pollen, water vapor, Smoke, and dust are main agents for
the scattering.
The amount of scattering is more in forward direction
The scattering takes place below 4.5 km of the atmosphere.
MIE SCATTERING

8. Non-selective scattering: affects all waves.
particles greater than 10 times the wavelength of the incident
energy.
The scattering takes place in the lowest portions of the atmosphere.
The water droplets and ice crystals (that makes clouds and fog banks)
- scatter all wavelength of visible light equally, causing the cloud
appear as white.
Non-selective scattering

9. Absorption is the process
by which the radiant
energy is absorbed and
converted into kinetic
energy. Or other forms
Agents which absorb the
radiant energy are
•Water vapor-
•CO2,
•O2,
•O3,
•N20 (nitrous oxide)
Atmospheric
windows

10. sensor
Cloud
Cloud
Zone of
no penetration
Earth Shadow

11. Refraction:
-Refers to the bending of light when it passes to from one
medium to another.
- the index of refraction (n) is a measure of the optical
density of a substance.
- ratio of (C/Cn) speed of light in vaccum and speed of light
in a substance.
- always greater than 1. for atmosphere it is 1.0002926.
- an effect produced by the movement of air masses in the
atmosphere with different refractive indices is called
ATMOSPHERIC SHIMMER.
- results in blurring on RS images.

12. Reflection:
- is a process whereby radiation “bounces off” an object like
the top of a cloud, a water body, or the terrestrial earth.
-Predictable direction in case of reflection.
- unpredictable direction in case of scattering.

13. Atmospheric Transmission

14. Atmospheric Windows
• Spectral regions where the EMR is passed through
without much attenuation.
• Spectral sensitivity range of eye
Coincides with both an atmospheric
Window and the peak level of
energy from the sun.
• Emitted energy from the earth , is
sensed through windows at 3 to 5µm
& 8 to 14µm using devices as thermal
Scanners.
•1mm to 1m: Radar & passive
Microwave systems.

15. Atmospheric Window
•It refers to the relatively transparent wavelength regions of
the atmosphere.
•The atmosphere is opaque in most of the regions. In some
regions of the electromagnetic spectrum, however it is
transparent.
•Remote sensing uses these transparent regions known as
windows to avoid the effects of absorption of radiation. The
most useful regions are:
The visible (0.4 to 0.76 Micrometer)
The reflected IR (0.76 to 3 Micrometer)
The thermal IR (8 to 14 Micrometer)