1. ELECTROMAGNETIC RADIATION
MER: form of energy emitted by sun, earth, atmosphere travels through space as electric and magnetic waves

2. Electromagnetic spectrum
Shortwave < 3 µm
Longwave > 3 µm

3. A blackbody is a perfect absorber of all the radiation it receives and emitter of max radiation possible at a given temp

4. Terrestrial (longwave): 100% infrared
Solar (shortwave) :
8% UV, X-ray, Gamma
47% visible
45% infrared
Terrestrial (longwave):
100% infrared

5. λ = wavelength

6. Atmospheric absorption
Gases in atmosphere absorb at different wavelengths.
Wavelengths not absorbed are TRANSMITTED.

7. absorption vs. transmission

8. Atmospheric absorption/transmittance graph
White gaps
are “atmospheric
windows of
transmission”;
black areas are
absorption bands

11. Longwave absorption

12. Atmospheric “window” of transmission:
Shortwave absorbers:
Ozone: absorbs UV < 0.3 μ
H2O vapor : absorbs > 0.8 μ
Atmospheric “window” of transmission:
0.3 – 0.8µ (shortwave)
Longwave absorbers:
H2O vapor, CO2, ozone, CH4, N2O
Another window:
8 – 11 µ (longwave)

13. Review SOLAR RADIATION: TERRESTRIAL RADIATION longwave (IR);
shortwave (visible, UV, IR);
higher radiation intensity;
absorbed by ozone and water vapor;
atmospheric window of transmission : 0.3 – 0.8 µ
TERRESTRIAL RADIATION
longwave (IR);
lower radiation intensity;
absorbed by “greenhouse gases” (O3, H2O, N2O, CO2,CH4)
atmospheric window of transmission : 8 – 11 µ

14. Solar constant
amount of solar radiation received at top of atmosphere on a plane surface perpendicular to sun’s rays.
(not diminished by atmosphere)
= 1372 W m-2
1 Watt = 1 J / sec

15. What is relationship
between wavelength
and temperature?
between energy

16. Rules of Radiation 1. Wein’s Law
all objects emit energy at wavelengths inversely proportional to their temperature
Wein’s Law gives wavelength of peak intensity (λmax)
λmax = 2897 / T (temp in Kelvins)

18. For earth:
λmax = 2897 / 300K = 9.6 μ (infrared)
For sun:
λmax = 2897 / 6000K = 0.48 μ (visible)
For molten lava? (temp = 1073 K)
λmax = 2897 / 1073 =
2.7 μ (shortwave infrared)

20. 2. Stefan-Boltzmann Law
E = σ (T4) (temp in Kelvins)
σ = Stefan-Boltzmann constant:
5.67x10-8 Wm-2 K-4

21. Humans maintain skin temp of 91°F (306 K). 1
Humans maintain skin temp of 91°F (306 K). 1. In which portion of the spectrum do we radiate? Wein’s Law: λmax = 2897 / temperature 2. How much energy do we radiate? Stefan-Boltzman : E = σ (T4) σ = 5.67x10-8 Wm-2 K-4
Lambda max = 9.5 microns (thermal IR)
SB: fourth power 306 = 8,767,700,496
E = 497 W/sq.m.