SCATTERING

GIS, CIMR;PU, LAHORE

1. Scattering Presented by: Maha Sabri Presented to: Mam.Rehana Jamal M.Sc (MCWM), CIMR, PUNJAB UNIVERSITY.

2. Interaction s o f E M Radiatio n wit h th e Atmosphere The most importan t source o f energ y i s the Sun. Before the Sun’s radiation reaches the Earth's surface i t ha s to travel through some distance of the Earth's atmosphere. The composition of the atmosphere is thus of importance in remote sensing becaus e EMR must pas s through i t i n orde r to reach the Earth’s surface.

3. Interaction s o f E M Radiatio n wit h th e Atmosphere The atmosphere also contains particles wit h a rang e o f sizes an d sources whic h ar e o f great importance in remote sensing. Composition of the atmosphere Component Percentage N 2 78.08 O 2 20.94 Ar 0.93 CO 2 0.0314 O 3 0.00000004

4. Interaction s o f E M Radiatio n wit h th e Atmosphere EMR interact s wit h particle s an d gase s i n the atmosphere . Three processe s serv e to attenuat e the signal w e ar e trying to detect Scattering : Redirectio n o f EMR f rom it s origina l path Absorption : Retention of EMR by molecules in the atmosphere Refraction: Passing o f EMR through the atmosphere

5. Scattering Scattering of electromagnetic radiation is caused by the interaction of radiation with matter resulting in the reradiation of part of the energy to other directions not along the path of the incident radiation. Scattering effectively removes energy from the incident beam. Unlike absorption, this energy is not lost, but is redistributed to other directions.

6. Scattering - Scattering is the redirection of EM energy by particles suspended in the atmosphere.  It is dependant upon the number of particles present in the atmosphere the size of the particles the wavemlength of incoming radiation and the depth of atmosphere that the radiation must travel through. 

7. Types of scattering Rayleigh scattering Mie scattering Non-selective scattering

8. Rayleigh Scattering Rayleigh scattering  , named after the British physicist Lord Rayleigh. Rayleigh scattering occurs when the size of the particle responsible for the scattering event is much smaller than the wavelength of the incident light. wave length dependant, favoring short wavelengths, and is responsible for our sky appearing blue.

9. Rayleigh scattering Scatters light in all directions Most effective at short wavelengths( blue,voilet ) hence blue sky

10. Rayleigh scattering Diameter of particles << wav elengt h o f EMR (small specks o f dus t o r N 2 and O 2 ) Rayleigh scattering causes shorter wavelengths of energy to b e scattered much more than longe r wavelengths. Rayleigh scattering is the dominant scattering mechanism in the uppe r atmosphere. The fact that the sky appear s "blue" durin g the da y is because of this phenomenon.

11. Blue light from the sun is scattered more than red so the sky is blue during the day. At sunset the angle of light is very low and the blue light is scattered away completely leaving only the less scattered red.

12. Why sky is blue? Figure showing the greater proportion of blue light scattered by the atmosphere relative to red light.

13. Why is the sky blue? As sunlight moves through the atmosphere, longer wavelengths( eg.red ) pass straight through . However, shorter wavelengths( eg.blue ) interact with gas molecules and scatter in the atmosphere

14. Mie scattering Diamete r o f particle s = wavelengt h o f EMR (Dust, smoke and water vapor) Dust , smoke an d wate r vapour a re common causes o f Mie scattering whic h tends to affec t longe r wavelength s than those affecte d b y Rayleigh scattering. Mie scattering occur s mostly i n the lowe r portion s o f the atmosphere where larger particles are more abundant, and dominates when cloud conditions are overcast.

15. Nonselective scattering Diamete r o f particle s >> wavelengt h o f EMR (Water droplets and large dust particles) This occur s whe n the particle s ar e much large r than the wavelength of the radiation. Water droplets and large dust particle s can cause this type o f scattering. Nonselectiv e scatterin g get s it s nam e from the fact that all wavelengths are scattered about equally.