All remote sensing radiation passes through the atmosphere both before and after it interacts with the Earth’s surface. The atmosphere changes the frequency, intensity, and direction of radiation.
The effects of the atmosphere on remotely sensed imagery are complex and varied.
Radiance measured by an air- or space-borne sensor is influenced by a variety of factors, not just diffuse sky irradiance between the sensor and the target on Earth’s surface.
The atmosphere primarily affects visible and infrared wavelengths, with only minor effects on microwave wavelengths.
what is the most common interaction then?
- scattering
The redirection of electromagnetic radiation by particles suspended in the atmosphere is known as scattering. The amount of scattering that occurs is determined by the size of the atmospheric particles, their abundance, the wavelength of the electromagnetic radiation, and the depth of the atmosphere.
it has four different categories
- Rayleigh scattering
- Mie Scattering
- Non-selective scattering
- Raman scattering
a. Rayleigh scattering
Lord Rayleigh discovered it in the 1890s, for which he received the Nobel Prize in Physics in 1904. Gases in the upper atmosphere, specifically particles smaller than the wavelength of the radiation, cause this type of scattering.
b. Mie Scattering
Gustav Mie discovered it in the early 1900s. This type of scattering involves particles the same size as the wavelength of the radiation.
This type of scattering is caused by water vapour and dust, both of which are found in the lower atmosphere, especially in the visible part of the spectrum.
Mie scattering, in contrast to Rayleigh scattering, is much less wavelength dependent.
c. Non-selective scattering
is caused by particles that are many orders of magnitude larger than the incident radiation (e.g. water droplets and large dust particles).
It usually takes place at a lower altitude. Non-selective scattering does not depend on wavelength; all wavelengths are scattered equally. The primary cause of haze in remotely sensed imagery is this type of scattering.
d. Raman scattering
Sir C.V. Raman discovered it in 1928. This type of scattering occurs when a photon collides with molecules, resulting in an energy loss or gain. This type of scattering can change the wavelength of radiation and is associated with atmospheric particles of any size or material.
