Revision as of 22:39, 30 June 2016

Section 8.1: Ionosphere

Atmosphere gets thinner as you go further away
At 30 miles in altitude, gets thin enough that UV rays can knock electrons away from molecules
Gas is ionized by loss of electron, positively charged ion, negative free electron
Ion + electron respond to voltage, like electrons in conductor
Atmospheric layer - ionosphere - becomes weak conductor
Ionosphere extends to 300 miles above surface of Earth

Regions:

ISS orbits 200 miles above Earht
Ionosphere arranged into multiple layers (D, E, F layers)
D layer - 30-60 miles, only present when illuminated by sun
E layer - 60-70 miles, similar to D region, lasts longer after sunset
F layer - 100-300 miles, least dens,e partially ionized at night
- F1 layer/F2 layer - split during day, recombine at night
- Height of regions vary with season, TOD, latitude, solar activity
- F2 is highest layer, reaches highest point at noon

Reflection and absorption

Weak conduction of layers allows bending/refracting of waves
Layers of ionosphere can bend waves
Bending o waves depends on ionization level, and wave frequency
VHF/UHF waves hardly bent at all
HF waves bent, can be reflected back to Earth
Weaker bending requires lower takeoff angles, otherwise waves lost to space
Critical angle - angle above which all energy lost to space
Critical frequency - frequency above which all energy lost to space (if pointed straight up)
Ionosonde - device used for measuring reflection of radio waves by ionosphere
Absorption is the enemy of propagation
In D and E layers, waves pass through denser gas regions, absorbed as they are refracted
For HF bands, below 10 MHz, AM broadcast bands, the D layer completely absorbs radio waves
Absorption increases with sunlight, ionization, more UV, and lower frequencies

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 ** Height of regions vary with season, TOD, latitude, solar activity
 ** F2 is highest layer, reaches highest point at noon
+Reflection and absorption
+* Weak conduction of layers allows bending/refracting of waves
+* Layers of ionosphere can bend waves
+* Bending o waves depends on ionization level, and wave frequency
+* VHF/UHF waves hardly bent at all
+* HF waves bent, can be reflected back to Earth
+* Weaker bending requires lower takeoff angles, otherwise waves lost to space
+* '''Critical angle''' - angle above which all energy lost to space
+* '''Critical frequency''' - frequency above which all energy lost to space (if pointed straight up)
+* '''Ionosonde''' - device used for measuring reflection of radio waves by ionosphere
+* Absorption is the enemy of propagation
+* In D and E layers, waves pass through denser gas regions, absorbed as they are refracted
+* For HF bands, below 10 MHz, AM broadcast bands, the D layer completely absorbs radio waves
+* Absorption increases with sunlight, ionization, more UV, and lower frequencies
 ===Section 8.1 Summary===
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