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Energy Sources and Radiation Principles

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Energy Sources and Radiation Principles GEO 410 Dr. Garver 69% absorbed + 31 reflected = 100% 45% absorbed by surface 21% + 3% absorbed by atm. Earth-atmosphere ... – PowerPoint PPT presentation

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Title: Energy Sources and Radiation Principles


1
Energy Sources and Radiation Principles
GEO 410 Dr. Garver
2
Electromagnetic Sensors
  • Operate from airborne spaceborne platforms.
  • Acquire data on the way Earths features emit and
    reflect energy.

3
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4
How is Energy Transferred?
a) Energy may be conducted directly from one
object - pan is in direct physical contact with
hot burner. b) Sun bathes Earths surface with
radiant energy causing air near ground to
increase in temperature - less dense air rises,
creating convectional currents in atmosphere. c)
Electromagnetic energy in the form of waves are
transmitted through vacuum of space from Sun to
Earth.
Jensen 2005
5
Basic wave theory
  • C vl (1.1)
  • All forms of energy are similar radiate in
    accordance to wave theory
  • Light travels as c
  • l distance between peaks
  • V cycles per second past a fixed point
  • Photons move at the speed of light
  • Move as waves

6
Particle Theory (1.2, 1.3)
  • EMR composed of discrete units
  • photon - fundamental unit of EM radiation.
  • Underlying basis for r.s. is measuring the
    varying energy levels.
  • Variations in photon energies are tied to
    wavelength or its inverse, frequency.
  • EM radiation varies from high to low energy
    levels, comprises electromagnetic spectrum.

7
Photon travels as an EM wave, two components,
oscillating as sine waves
C
Fig. 1.2
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11
  • Radiation from specific parts of EMS contain
    photons of different wavelengths.
  • EMR extends over wide range of wavelengths.
  • Photon energy is measured at detectors
  • electromagnetic (EM) spectrum - continuum of all
    radiant energies
  • Other wave types require a carrier (water)
  • Photon waves can transmit through a vacuum
    (space).

12
  • Images made from data acquired as electronic
    signals, rather than recorded on film.
  • Produced by sensors operating in the visible and
    near-IR.
  • Some radar and thermal sensors.

13
  • EMS intervals and descriptive names
  • visible region - 0.4 and 0.7 microns
  • infrared region 0.7 to 100 microns(1) reflected
    IR 0.7 to 3.0 microns(2 ) thermal bands 3 to
    100 microns
  • 3 to 5 microns, and 8 to 14 microns.
  • microwave region - 0.1 to 100 cm, includes
    interval used by radar systems.

14
Energy and Radiation
  • The dividing line between reflected and emitted
    IR wavelengths is 3 ?m.
  • below 3 ?m reflected energy
  • above 3 ?m emitted

15
Primary source of energy is the Sun
  • Solar irradiation arrives at Earth-at wavelengths
    determined by temperature of sun (6000 K).
  • As solar rays arrive at Earth, atmosphere absorbs
    or reflects (backscatters) a fraction and
    transmits remainder.

16
  • Visible 0.4-0.7 mm Sun
  • Thermal IR 10 mm Earth

17
2 Important Laws
  • Stefan Boltzman Law the hotter the object the
    more energy it emits
  • Weins Law the hotter the object the shorter
    the wavelengths emitted

18
SB Law
  • M sT4
  • T temperature of emitting body
  • s SB constant
  • M total energy emitted
  • Energy emitted increases rapidly with inc. T.

19
Weins Law
  • lm A/T
  • lm maximum wavelength
  • A constant
  • T temperature, K

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21
Kelvin Celsius 273.15 Celsius 5/9 x
(Fahrenheit -32) Fahrenheit (Celsius/(5/9))32
22
  • Solar Constant - Insolation at top of atm. 1372
    Wm-2
  • Peak in the blue region.
  • Insolation - Solar radiation that reaches a
    horizontal plane at Earth

23
Global Net Radiation
24
  • Land, ocean , and atmosphere - incoming radiation
    partitioned into
  • Transmission
  • Absorption
  • Reflection
  • Scattering

25
Transmission, Absorption, Scattering, and
Reflection.
  • photons passing through medium (usually air)
    experience one or more reactions

26
Energy gained/lost by Earth/Atm.
  • Transmission - passage of energy
  • Reflection - energy not absorbed, no change in
    wavelength, the angle of reflection of a light
    ray is the same as the angle of incidence.

27
Energy gained/lost by Earth/Atm.
  • Absorption - conversion of radiant energy to heat
    energy
  • In atmosphere Ozone, carbon dioxide and water
    vapor absorb at various wavelengths.
  • Ozone UV
  • CO2, water vapor trap heat for Earth
  • See atmospheric windows figure

28
Scattering
  • Some particles and molecules found in the
    atmosphere have the ability to scatter solar
    radiation in all directions.
  • Different from reflection (where radiation is
    deflected in one direction)
  • 3 Types

29
  • Rayleigh scattering - Caused by constituents
    (O2, N2 CO2 and water vapor) that are much
    smaller than the radiation wavelengths.
  • Increases with shorter wavelengths (blue sky
    effect).
  • A target is a Rayleigh scatterer if Dltltl

30
  • WHY IS THE SKY BLUE?
  • Rayleigh scattering.
  • Longer wavelengths pass straight through atm.
  • Not much red, orange and yellow light is
    affected.
  • Shorter wavelengths scattered by gas molecules in
    different directions (blue).

31
  • 2. Mie scattering - atmospheric constituents
    (i.e., smoke, dust, water vapor) whose dimensions
    are of the order of the radiation wavelengths.
  • D l, then the target is a Mie scatterer.
  • where D is the diameter of the target.

32
3. Non-selective ScatteringIf D gtgt l, then the
target is a non-selective scatterer. Water
droplets, large particles.All l scattered
equally (fog, clouds)
33
Atmospheric scatter can be 80 to 90 of signal
observed by a sensor. Makes an image hazy, low
contrast.
34
69 absorbed 31 reflected 100
21 3 absorbed by atm.
45 absorbed by surface
35
Earth-atmosphere energy balance
  • Follow 100 units of solar input
  • 31 reflected to space (albedo)
  • 21 absorbed by clouds, dust, gases
  • 3 absorbed by O3 in stratosphere
  • 45 absorbed by surface
  • 100
  • 69 re-radiated to space

36
Global Net Radiation
37
Albedo energy reflected
  • Blacktop or snow?
  • Avg. albedo of Earth 30
  • Clouds and volcanoes

38
Earths Avg. 31
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40
  • From previous graph
  • Calculate decrease in energy between solar
    constant and Earths surface in visible peak.
  • Radiance W sr-1 m-2
  • Irradiance W m-2

41
  • Steradian - used to measure "solid" angles
  • related to surface area of a sphere the same way
    a radian is related to the circumference of a
    circle.
  • A Radian "cuts out" a length of a circle's
    circumference equal to the radius.
  • A Steradian "cuts out" an area of a sphere equal
    to (radius)2.

42
  • Exercise 1 question 3
  • Peak at ______ nm of irradiance curve for
    sunlight as it reaches the outer atmosphere.
  • Spectral irradiance reads _____ W/m-2/nm
  • Sea level irradiance curve at the same peak
    position _____ W/m-2/nm

43
The atmosphere messes things up
  • Most r.s. is conducted above Earth within or
    above atmosphere.
  • Gases in atmosphere interact with incoming solar
    energy and outgoing infrared from the Earth's
    surface.
  • The atmosphere itself is excited by EMR, becomes
    another source of released photons.

44
Atmospheric windows white areas
45
2 Energy Sources Used in R. S.
R. S. is limited to Atmospheric Windows
Common Sensors
46
  • Blue zones - minimal passage incoming and/or
    outgoing radiation
  • White areas - atmospheric windows
  • Most r.s. instruments operate in windows by
    detectors tuned to wavelengths that pass through
    atmosphere.
  • Some sensors, meteorological satellites, directly
    measure absorption phenomena - CO2.

47
  • Opacity - measure of impenetrability to
    electromagnetic radiation, especially visible
    light.
  • An opaque substance transmits very little light,
    and therefore reflects, scatters, or absorbs most
    of it.

48
Remote sensing of the Earth
  • Reflected energy in vis, near and mid IR
  • Most r. s. systems designed to collect reflected
    radiation.
  • Emitted energy in thermal IR and microwave
  • Signals analyzed numerically - image variations
    represent different intensities of photons
  • multispectral remote sensing gathering of
    continuous or discontinuous ranges of wavelengths.

49
Images made from varying wavelength/intensity
signals
  • astronomical body viewed through telescopes
    equipped with different multispectral sensing
    devices.
  • four views of Crab Nebula, now in a state of
    chaotic expansion after a supernova explosion
    first sighted in 1054 A.D. by Chinese astronomers.

50
Multispectral Remote Sensing
IR
Radio
X-ray
Visible
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