LWIR TRANSMISSION

Question 1

SURFACE TRANSMISSION

Answer 1

Blackbody
Peak 15micron
Range often quoted 13-17micron with most effect at wings

Question 2

LWIR and CO2

Answer 2

Finite amount of continuously radiated 13-17 (from now on 15) micron LWIR
15μ corresponds to a line with frequency f15
CO2 has harmonic of f
Therefore CO2 ‘sees’ and reacts to f15

Question 3

BLACKBODY SHELL THEORY

Answer 3

CO2 valence electron absorbs e due to f15 photon and goes to higher e state

A short time later (femtosecond) electron returns to ground stage and photon emitted (at same e and f as absorbed)

• ? Point source, photon energy as an expanding sphere of energy
  
  • Thereby constructing the next BB ‘shell’
• Therefore 50% toward space and 50% to the surface (the ‘heating effect)
• Think angles over 180° hemisphere DOWN: argue that max effect is directly down; rest decreasing in effect as horizon is neared; however, each photon which interacts with another CO2 molecule will repeat this process
• Likewise the ‘upwards’ hemisphere photons will have the same process until the concentration of CO2 molecules reaches a level where very few interactions occur

Problem is only a small amount of 15μ LWIR is seen at TOA, implying most of the emitted energy is returned to the surface

Question 4

A MECHANICAL ENGINEER’S DREAM

Answer 4

The CO2 molecule ‘sees’ the 15μ radiation and absorbs the photon

It is a dipole molecule and it vibrates at its ‘fingerprint’ vibration

• Increasing it’s own e level and
• Increasing the P of collision with the other molecules surrounding it (2500j
• Raising the TOTALe of the system
  
  • And, therefore, the temperature

The energy of the absorbed photon is redistributed to the system and is NOT emitted