1. Physical Principles of Remote Sensing: Electromagnetic Radiation-

2. Outline Properties of electromagnetic radiation
The electromagnetic spectrum
The Planck, Stefan-Boltzmann, and Wien’s equations
Spectral emissivity
Radiant temperature vs. kinetic temperature -

3. Energy Transfer
Energy is “the ability to do work” -

4. Electromagnetic Radiation
EMR is the source for most types of remote sensing
Passive -
Active

5. Electrical (E) and magnetic field (B) are orthogonal to each other
Direction of each field is perpendicular to the direction of wave propagation. -

6. Electromagnetic Waves
Described by:
Wavelength
Frequency
Amplitude -

7. Frequency vs. Wavelength
l = distance of separation between two successive wave peaks
= number of wave peaks passing in a given time
The product of wavelength and frequency is a constant:
c=n l
c = speed of light in a vacuum = 3.0 108 ms-1 -

8. Electromagnetic Radiation
Its harmonic wave form can be described according to the Maxwell equations:
Where, E is the electric field
Eo is a constant vector
= angular frequency (2pn), n = c/l,
l = wavelength
c = speed of light in a vacuum (300,000,000 ms-1)
k = wavenumber (2p/l)
x = distance along the x-axis
t = time
The value of E at any point depends only on x and t -

9. Energy vs. Frequency
When considering the particle form of energy, we call it a photon
The energy of a photon, Q, is proportional to its frequency, n:
Q = h n
n = c/l
Q = hc/l
h = Planck’s constant = 6.63 10-34 Js
c = speed of light = 3.0 108 ms-1
Thus,
Q ~ 1/l -

10. The EM Spectrum -

11. Blackbody Radiation
All objects whose temperature are above absolute zero Kelvin ( oC) emit radiation at all wavelengths
A “blackbody” is one that is a perfect absorber and perfect emitter (hypothetical, though Earth and Sun are close) -

12. Stefan-Boltzmann equation:
Planck’s equation:
Stefan-Boltzmann equation:
Wien’s displacement equation:
c speed of light  108 ms-1
h Planck constant  Js
k Boltzmann constant  JK-1
 Stefan-Boltzmann constant  10-8 Wm-2K-4 -

13. What do they mean??
Planck equation gives the radiance of an object at a given temperature at any wavelength
Stefan-Boltzmann equation describes the total amount of energy being radiated
Wien’s equation describes the wavelength of maximum radiation -

14. Planck Equation, continued
Planck’s equation describes how heat energy is transformed into radiant energy
According to Planck’s law, an object will emit radiation in all wavelengths but not equally
This is the basic law for radiation measurements in all parts of the EM spectrum -

15. Examples using Wien’s Displacement Equation
Tsun= 5800K
Peak of Sun’s radiation =
2898mmK / 5800K = 0.5 mm
Tearth = 288K
Peak of Earth’s radiation =
2898mmK / 288K = 10 mm -

16. Graybody Radiation an object that is not a perfect absorber/emitter
it reflects part of incident radiation
emissivity, e, is the ratio of graybody exitance to blackbody exitance -

17. Emissivity
Describes the actual energy absorption and emission properties of real objects (“graybodies”)
Is wavelength dependent (so, it’s actually a “colored body”)
Emissivity establishes the radiant temperature Trad of an object -

18. Blackbody Radiation Stefan-Boltzmann equation:
Radiant exitance (M) is proportional to physical temperature
This assumes a “blackbody” which is a perfect emitter and a perfect absorber -

19. Radiant Temperature vs. Kinetic Temperature
Two objects can have the same kinetic temperature but different radiant temperatures
Object
Emissivity
Kinetic Temperature
Radiant
Temperature
Blackbody
1.0
300
Water, distilled
0.99
299.2
Basalt, rough
0.95
296.2
Basalt, smooth
0.92
293.8
Obsidian
0.86
288.9
Mirror
0.02
112.8 -

20. Terminology (yuck!) Radiant flux f, units W
Irradiance (flux density), E units Wm-2 (called Exitance, M when it is away from the surface)
Radiance, L, units Wm-2 sr-1
Note, all can be functions of wavelength with additional units mm-1 -

21. Sun’s Radiant Energy Distribution
Name of Spectral Region
Wavelength Range, mm
Percent of Total Energy
Gamma and X-rays
< 0.01
Negligible
Far Ultraviolet
0.02
Middle Ultraviolet
1.95
Near Ultraviolet
5.32
Visible
43.5
Near Infrared
36.8
Middle Infrared
12.0
Thermal Infrared
0.41
Microwave
> 1000
Radio Waves -

22. More about radiation
Energy emitted from the Sun is enormous: 6.4  107 Wm-2
It is reduced to 1370 Wm-2 at the top of the Earth’s atmosphere because of the Earth-Sun distance (1/r2)
An object at 288K emits only 390 Wm-2 -

23. Solar Emittance Curve Radiation leaving the surface of the sun
Solar radiation at sea level -

24. For terrestrial remote sensing, the most important source is the sun
Reflected solar energy is used mm
The Earth is also an energy source
>6 mm for self-emitted energy -

25. -