refer to: Radiation
Atmospheric Windows to Electromagnetic Radiation
Effects of The Ionosphere on The Lower End of The Radio Spectrum
The ionized part of the Earth’s atmosphere is known as the ionosphere. Ultraviolet light from the sun collides with atoms in this region knocking electrons loose. This creates ions, or atoms with missing electrons. This is what gives the Ionosphere its name and it is the free electrons that cause the reflection and absorption of radio waves.
When the sun is overhead during the day, most of the ionosphere is ionized due to the large amount of ultraviolet light coming from the sun. As radio waves enter Earth’s atmosphere from space some of the waves are absorbed by the electrons in the ionosphere while others pass through and are detectable to ground based observers. The frequency of each of these waves is what determines whether or not it is absorbed or able to pass through the atmosphere. Low frequency radio waves do not travel very far through the atmosphere and are absorbed rather quickly. Higher frequency waves are able to pass through the atmosphere entirely and reach the ground.
This process also works in reverse for radio waves produced on the earth. The ultra high frequency waves pass through the ionosphere and escape into space while the lower frequency waves reflect off the ionosphere and essentially “skip” around the earth.
Radio Waves
Radio waves fall into three main categories with a variety of uses
|
Category |
Frequency |
Description |
|---|---|---|
|
H.F. High Frequency |
3-30 MHz |
Long Range communications. Shipping, Aircraft, World Broadcast Communications, AM Radio. |
|
V.H.F. Very High Frequency |
30-300 MHz |
Medium range communications. Fleet vehicles, mobile, coastal shipping and air to tower communications. |
|
U.H.F. Ultra High Frequency |
300-3000 MHz |
This is the domain of such things as Police handheld radios, cell-phones, T.V., and spacecraft to ground communications. In the high U.H.F. range the signal can “bounce” off buildings and reflect until it is detected by a receiver. |
Effects of CO2 and H2O on The Microwave-Infrared Spectrum
TODO
Effects of Ozone and Molecular Oxygen on The UV-Xray-Gmma Spectrum
TODO