Interaction of EM with atmosphere

1. Interaction of EM with atmosphere Mirza Muhammad Waqar Contact: mirza.waqar@ist.edu.pk +92-21-34650765-79 EXT:2257 RG610 Course: Introduction to RS & DIP

2. Outlines • Remote Sensing System • The Energy Source • The Atmosphere • The Energy-Matter Interaction at the Earth’s Surface • The Sensor • The data processing and supply system • The multiple data users • An ideal Remote Sensing System

3. Remote Sensing System

4. Electromagnetic Radiations • c = f λ • c = 3x108 m/sec • Either f , λcan be used for characterization of EM radiations.

5. Electromagnetic Radiation • Remote sensing is based on detecting electromagnetic (EM) energy. • Since the speed of light is constant, wavelength and frequency are inversely related to each other.

6. Electromagnetic Radiation

7. Black Body Radiations

8. Energy Interactions in the Atmosphere • Irrespective of its source, all radiations detected by remote sensors passes through some distance of atmosphere • The path length can vary widely depending upon • Source of illumination elevation angle • Sensor view angle • Following phenomena can take place, while interaction of energy in atmosphere. • Scattering • Absorption

9. 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. • Type of Scattering • Raleight Scattering • Mie Scattering • Non Selective Scattering

10. Rayleigh Scatter • Rayleigh scatter is common when radiation interacts with atmospheric molecules and other tiny particles that are much smaller in diameter than the wavelength of interacting radiation. • The effect Rayleigh scatter is inversely proportional to the fourth power of wavelength. • Hence shorter wavelengths will scatter more by Rayleigh scatter.

11. The Blue Sky ~ • A “blue” sky is a manifestation of Rayleigh scatter. • In the absence of scatter, the sky would appear black. • Sunlight interacts with the earth’s atmosphere, • It scatter the shorter (blue) wavelength more dominantly than the other visible wavelengths. • Consequently, we see a blue sky.

12. Mie Scattering • Mie scattering occur when atmospheric particle diameters essentially equal the wavelengths of the energy being sensed. • Water vapors, dust particles are major causes of Mie scatter. • Mie scatter influence longer wavelengths as compared to the Rayleigh scatter.

13. Non-Selective Scattering • It occurs when the diameter of the particles causing scatter are much larger than the wavelengths of the energy being sensed. • Water droplets, for example causes such scatter. • This scattering is “nonselective” with respect to wavelength. • Hence in visible, equal quantities of blue, green and red light are scatter, hence fog and cloud appear white in satellite images.

14. Absorption • Atmospheric absorption results in the effective loss of energy. • The most efficient absorbers of solar radiation in atmosphere are • Water vapor • Carbon dioxide • Ozone • The wavelength range in which the atmosphere is particularly transmissive of energy are referred to as atmospheric windows.

15. Atmospheric Windows • The wavelength ranges in which the atmosphere is particularly transmissive of energy are referred to as atmospheric windows.

16. Questions & Discussion