Natural ElectroMagnetic Interference (EMI) is caused by natural sources of EMI such as rain spray, storms, solar radiation, electrical storms, and cosmic noises. Natural sources of EMI are broadly classified in two main categories:
1. Terrestrial source:
- Such type of Natural sources of EMI include natural emissions coming from earth’s surface. These sources are :
When an aircraft flies through clouds under conditions of storms and lighting, an electric charge accumulates over its surface. This charge distribution is more towards corners and points sides of the airplane and leaks to the grounds from such pints in the for of corona discharge. The resultant voltage of corona discharge ranges from 40,000 volts to 10,00,000 volts. The EMI created by such discharge is known as precipitation static.
Atmospheric Noise :
Atmospheric noise is random in nature and is characterized by randomly recurring pulses. Such noise is not limited to a particular band. Atmospheric noise is produced by electrical discharges occurring during thunderstorms and lightning
2. Extra-Terrestrial source :
Such type of Natural sources of EMI include natural emissions coming from earth’s surface. These sources are :
Solar Radiations :
Solar radiations generates from sources in the region of Sun and its corona. The resultant noise varies in all frequencies at different degrees. The intensity of solar radiation varies with a periodicity from weeks to months and corresponds to sun-spot activity.
Cosmic Noise :
Cosmic noises consists of short duration randomly recurring pulses. Significant source of cosmic noise includes Moon and Jupiter. On the surface of earth, cosmic noise is confined to VHF and UHF bands.
Sky- Background Noise :
It is also called as Galactic Noise. It is produced by radio stars. Radio stars refers to the stars which are optically not visible. Presently only few Radio stars with potential to create EMI are known. However, low noise receivers are being used to discover more and more Radio stars.