Remote Sensing from Space

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Remote Sensing from Space

• C5646

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Course Layout

• Lectures
• Practicals
• Assessment

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Lectures

• Week 1
• Introduction, course layout
•  
• Week 2
• The electromagnetic energy, energy source, wave
  theory,
• particle theory,
•  
• Week 3
• The electromagnetic spectrum
•  
• Week 4
• Radiation and the atmosphere, spectral signature

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Lectures

• Week 5
• Image display, sensors and platforms
•  
• Week 6
• Spectral Resolution, spatial resolution, temporal
  resolution
•  
• Week 7
• Test No. 1
• Remotely sensed images, multispectral images,
  type of images
•  
• Week 8
• Passive sensors, active sensors
•  

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Lectures

• Week 9
• Image Interpretation and analysis, visual
  interpretation, element of visual interpretation
•  
• Week 10
• Digital image processing, preprocessing, image
  enhancement
•  
• Week 11
• Image transformation, image classification and
  analysis
•  
• Week 12
• Image classification, information and spectral
  classes

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Lectures

• Week 13
• Supervised classification, unsupervised
  classification
•  
• Week 14
• Test No. 2
• Radar, basic principles, radar system in remote
  sensing
• Week 15
• Range resolution, radar geometry, radar images

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Practicals

• Digital Image Processing
• Print intro_e.pdf
• exerc_e.pdf
• Hands-on assignments to be handed in before week
  14
• Project Proposal Assigment
• see AssignX.pdf
• Date Due week 8

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Practicals

• Digital Image Processing
• Print intro_e.pdf
• exerc_e.pdf
• Hands-on assignments to be handed in before week
  14
• Project Proposal Assigment
• see AssignX.pdf
• Date Due week 8

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Assesment

• Test 2x 30
• Coursework (2) 20
• Final Exam 50
• Total 100

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Remote Sensing

• Remote Sensing is the acquisition and
  measurement of data/information on some
  property(ies) of a phenomenon, object, or
  material by a recording device not in physical,
  intimate contact with the feature(s) under
  surveillance
• Techniques involve amassing knowledge pertinent
  to environments by measuring force fields,
  electromagnetic radiation, or acoustic energy
  employing cameras, lasers, radio frequency
  receivers, radar systems, sonar, thermal devices,
  and other instruments.

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Remote Sensing

• Remote Sensing The techniques for collecting
  information about an object and its surroundings
  from a distance without contact
• Components of Remote Sensing
• the source, the sensor, interaction with the
  Earths surface, interaction with the atmosphere

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Mechanisms
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Remote Sensing Principle
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Some Basic Terms

• Spectral response is a characteristic used to
  identify individual objects present on an image
  or photograph
• Resolution describes the number of pixels you can
  display on a screen device
• Spatial resolution is a measure of the smallest
  separation between two objects that can be
  resolved by the sensor

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The First Application of Remote Sensing
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A Brief Chronology of Remote Sensing

• 1826 - The invention of photography
• 1960s - The satellite era, and the space race
• between the USA and USSR.
• 1960s - The setting up of NASA.
• 1960s - First operational meteorological
• satellites
• 1960s - The setting up of National
• Space Agencies

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A Brief Chronology of Remote Sensing

• 1970s - Launching of the first generation of
  earth resource satellites
• 1970s - Setting up of International Remote
  Sensing Bodies
• 1980s - Setting up of Specific Remote
  Sensing Journals
• - Continued deployment of Earth
• Resource satellites by NASA
• 1990s - Launching of earth resource
  satellites by national space agencies and
  commercial companies

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A Brief Chronology of Remote Sensing

• Satellite remote sensing first received
  operational status in 1966 in the study of
  meteorology.
• At this stage a series of orbiting and
  geo-stationary American satellites were
  inaugurated, with the intention that they would
  yield information to any suitably equipped and
  relatively modestly priced receiver anywhere in
  the world.

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Wave Theory

• Electromagnetic radiation consists of an
  electrical field (E) which varies in magnitude in
  a direction perpendicular to the direction in
  which the radiation is travelling, and a magnetic
  field (M) oriented at right angles to the
  electrical field.
• Both these fields travel at the speed of light (c)

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Wavelength and Frequency

• Wavelength is measured in metres (m) or some
  factor of metres such as
• nanometers (nm, 10-9 metres),
• micrometers (?m, 10-6 metres) or
• centimetres (cm, 10-2 metres).
• Frequency refers to the number of cycles of a
  wave passing a fixed point per unit of time.
  Frequency is normally measured in hertz (Hz),
  equivalent to one cycle per second, and various
  multiples of hertz.

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Wave Theory

• From basic physics, waves obey the general
  equation
• c v l
• Since c is essentially a constant (3 x 108
  m/sec), frequency v and wavelength l for any
  given wave are related inversely, and either term
  can be used to characterise a wave into a
  particular form.

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Particle Theory

• Particle (Quantum) theory suggests that EM
  radiation is composed of many discrete units
  called photons or quanta. The energy of a quantum
  is given as
• Q h.v
• where
• Q energy of a quantum (Joules - J)
• h Planks constant, (6.626 x 10-34 J/sec)
• v frequency

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Particle Theory

• We can combine the Wave and Particle theories for
  EM radiation by substituting v c/l in the
  above equation. This gives us
• Q h.c
• l
• From this we can see that the energy of a quantum
  is inversely proportional to its wavelength.
  Thus, the longer the wavelength of EM radiation,
  the lower its energy content.

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Particle Theory

• This has important implications for remote
  sensing from the standpoint that
• Naturally emitted long wavelength radiation
  (e.g. microwaves) from terrain features, is more
  difficult to sense than radiation of shorter
  wavelengths, such as emitted thermal IR.
• Therefore, systems operating at long wavelengths
  must view large areas of the earth at any given
  time in order to obtain a detectable energy signal

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Electromagnetic Spectrum
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Electromagnetic Spectrum

• The electromagnetic spectrum ranges from the
  shorter wavelengths (including gamma and x-rays)
  to the longer wavelengths (including microwaves
  and broadcast radio waves).
• There are several regions of the electromagnetic
  spectrum which are useful for remote sensing.

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Visible Spectrum

• The light which our eyes - our "remote sensors" -
  can detect is part of the visible spectrum.
• It is important to recognise how small the
  visible portion is relative to the rest of the
  spectrum.
• There is a lot of radiation around us which is
  "invisible" to our eyes, but can be detected by
  other remote sensing instruments and used to our
  advantage.

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Visible Spectrum

• The visible wavelengths cover a range from
  approximately 0.4 to 0.7 ?m.
• The longest visible wavelength is red and the
  shortest is violet.
• It is important to note that this is the only
  portion of the EM spectrum we can associate with
  the concept of colours.

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VIOLET 0.400 - 0.446 mm BLUE 0.446 - 0.500
mm GREEN 0.500 - 0.578 mm YELLOW 0.578 -
0.592 mm ORANGE 0.592 - 0.620 mm RED 0.620
- 0.700 mm
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Visible Spectrum

• Blue, green, and red are the primary colours or
  wavelengths of the visible spectrum.
• They are defined as such because no single
  primary colour can be created from the other two,
  but all other colours can be formed by combining
  blue, green, and red in various proportions.
• Although we see sunlight as a uniform or
  homogeneous colour, it is actually composed of
  various wavelengths.
• The visible portion of this radiation can be
  shown when sunlight is passed through a prism,

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Infrared(IR)Region

• The IR Region covers the wavelength range from
  approximately 0.7 ?m to 100 mm - more than 100
  times as wide as the visible portion!
• The infrared region can be divided into two
  categories based on their radiation properties -
  the reflected IR, and the emitted or thermal IR.

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Reflected and Thermal IR

• Radiation in the reflected IR region is used for
  remote sensing purposes in ways very similar to
  radiation in the visible portion. The reflected
  IR covers wavelengths from approximately 0.7 mm
  to 3.0 mm.
• The thermal IR region is quite different than the
  visible and reflected IR portions, as this energy
  is essentially the radiation that is emitted from
  the Earth's surface in the form of heat. The
  thermal IR covers wavelengths from approximately
  3.0 mm to 100 mm.

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Microwave Region

• The portion of the spectrum of more recent
  interest to remote sensing is the microwave
  region from about 1 mm to 1 m.
• This covers the longest wavelengths used for
  remote sensing.
• The shorter wavelengths have properties similar
  to the thermal infrared region while the longer
  wavelengths approach the wavelengths used for
  radio broadcasts.

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Radiation Emission
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Emission of Radiation from Energy Sources

• Each energy/radiation source, or radiator, emits
  a characteristic array of radiation waves.
• A useful concept, widely used by physicists in
  the study of radiation, is that of a blackbody.
• A blackbody is defined as an object or substance
  that absorbs all of the energy incident upon it,
  and emits the maximum amount of radiation at all
  wavelengths.
• A series of laws relate to the comparison of
  natural surfaces/radiators to those of a
  black-body

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Stefan-Boltzmann Law

• All matter at temperatures above absolute zero
  (-273 oC) continually emit EM radiation. As well
  as the sun, terrestrial objects are also sources
  of radiation, though of a different magnitude and
  spectral composition than that of the sun.
• The amount of energy than an object radiates can
  be expressed as follows
• M s T4
• M total radiant exitance from the surface of a
  material (watts m-2)
• s Stefan-Boltzmann constant, (5.6697 x 10-8 W
  m-2 K-4)
• T absolute temperature (K) of the emitting
  material

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Stefan-Boltzmann Law

• It is important to note that the total energy
  emitted from an object varies as T4 and therefore
  increases rapidly with increases in temperature.
• Also, this law is expressed for an energy source
  that behaves like a blackbody, i.e. as a
  hypothetical radiator that totally absorbs and
  re-emits all energy that is incident upon
  it.actual objects only approach this ideal.

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Kirchoffs law

• Since no real body is a perfect emitter, its
  exitance is less than that of a black-body.
• Obviously it is important to know how the real
  exitance (M) compares with the black-body
  exitance (Mb)
• This may be established by looking at the ratio
  of M/Mb, which gives the emissivity (e) of the
  real body.
• M eMb
• Thus a black-body 1, and a white-body 0

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Weins Displacement law

• Just as total energy varies with temperature, the
  spectral distribution of energy varies also.
• The dominant wavelength at which a blackbody
  radiation curve reached a maximum, is related to
  temperature by Weins Law
• l m A
• T
• lm wavelength of maximum spectral radiant
  exitance, mm
• A 2898 mm, K
• T Temperature, K

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Some Basic Terms

• Upon Striking an Object the Irradiance Will Have
  the Following Response
• Transmittance - some radiation will penetrate
  into certain surface media such as water
• Absorptance - some radiation will be absorbed
  through electron or molecular reactions within
  the medium encountered
• Reflectance - some radiation will, in effect, be
  reflected (and scattered) away from the target at
  different angles

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Reflected Light Remote Sensing
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Light Interaction with Surfaces
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The Brightness of Surfaces - What Controls This?
(1) Reflectance
(2) Roughness and the BRDF
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Effect of Different Types of Scattering/Reflection
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(3) The Effect of Topography
On the shaded hill slopes, the sun's illumination
is spread over a larger area than on the sunny
slopes. So the amount of energy per unit area is
less. This means that there is less light
available for reflection, and the shaded hill
slopes are darker.
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The Effect of the Atmosphere on Spectral Data
Path Radiance (Lp)
Atmospheric Transmissivity (T)
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Energy Interactions with the Atmpsphere
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Energy Interaction with the Atmosphere

• Irrespective of source, all radiation detected by
  remote sensors passes through some distance (path
  length) of atmosphere.
• The net effect of the atmosphere varies with
• Differences in path length
• Magnitude of the energy signal that is being
  sensed
• Atmospheric conditions present
• The wavelengths involved.

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The Process

• Energy Source An energy source generates
  electromagnetic radiation (EMR) that illuminates
  objects it encounters.
• Radiation and the Atmosphere As the EMR
  encounters the atmosphere, only a fraction of it
  passes through to the ground.
• Radiation and the Surface EMR is absorbed,
  transmitted, or reflected by objects on the
  Earths surface.

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The Process

• Sensor records Radiation EMR that is reflected
  is then recorded by a sensor (via a satellite or
  other platform).
• Transmitting Sensor Data EMR data from the
  sensor is then transferred to a receiving center
  where it is transformed into an image.
• Data Analysis The data is analyzed and
  pertinent information is extracted.
• Remote Sensing Application The data is used to
  increase understanding about a particular locale
  or issue.

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B. Radiation and the Atmosphere

• When Electromagnetic Radiation
• (EMR) interacts with the
• atmosphere, one or more of the
• following three processes may
• occur
• Scattering
• Refraction
• Absorption

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Scattering

• Upon reaching the atmosphere, EMR encounters
  large molecules or particles that cause
  scattering. Water vapor and dust particles are
  examples of substances that contribute to
  scattering.Shorter wavelengths scatter more
  often than longer wavelengths.Since blue
  wavelengths are shorter than red or green
  wavelengths, they are scattered more easily,
  causing the sky to appear blue.

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Scattering

• Atmospheric scattering is the unpredictable
  diffusion of radiation by particles in the
  atmosphere.
• Three types of scattering can be distinguished,
  depending on the relationship between the
  diameter of the scattering particle (a) and the
  wavelength of the radiation (?).

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Scattering of EM energy by the atmosphere
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Rayleigh Scatter

• a lt ?
• Rayleigh scatter is common when radiation
  interacts with atmospheric molecules (gas
  molecules) and other tiny particles (aerosols)
  that are much smaller in diameter that the
  wavelength of the interacting radiation.
• The effect of Rayleigh scatter is inversely
  proportional to the fourth power of the
  wavelength. As a result, short wavelengths are
  more likely to be scattered than long
  wavelengths.
• Rayleigh scatter is one of the principal causes
  of haze in imagery. Visually haze diminishes the
  crispness or contrast of an image.

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Relationship between path length of EM radiation
and the level of atmospheric scatter
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Mie Scatter

• a ltgt ?
• Mie scatter exists when the atmospheric particle
  diameter is essentially equal to the energy
  wavelengths being sensed.
• Water vapour and dust particles are major causes
  of Mie scatter. This type of scatter tends to
  influence longer wavelengths than Rayleigh
  scatter.
• Although Rayleigh scatter tends to dominate under
  most atmospheric conditions, Mie scatter is
  significant in slightly overcast ones.

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Non-selective scatter

• a gt ?
• Non-selective scatter is more of a problem, and
  occurs when the diameter of the particles causing
  scatter are much larger than the wavelengths
  being sensed.
• Water droplets, that commonly have diameters of
  between 5 and 100mm, can cause such scatter, and
  can affect all visible and near - to - mid-IR
  wavelengths equally.
• Consequently, this scattering is non-selective
  with respect to wavelength. In the visible
  wavelengths, equal quantities of blue green and
  red light are scattered.

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Non-Selective scatter of EM radiation by a cloud
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Absorption

• In contrast to scatter, atmospheric absorption
  results in the effective loss of energy to
  atmospheric constituents.
• This normally involves absorption of energy at a
  given wavelength.
• The most efficient absorbers of solar radiation
  in this regard are
• Water Vapour
• Carbon Dioxide
• Ozone

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Absorption of EM energy by the atmosphere
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C. Radiation and the Surface

• Electromagnetic radiation that passes through
  the atmosphere interacts with the surface in
  three ways
• Reflection
• Absorption
• Transmission
• Reflection EMR that is reflected off of the
  surface
• Absorption EMR that is absorbed by the surface
• Transmission EMR that moves through a surface

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Reflection

• In remote sensing, reflection is a very
  significant factor for recording the Earths
  surface.There are two important types of
  reflection
• Specular
• Diffuse
• A surfaces reflectance is generally a
  combination of specular and diffuse reflection.

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Reflection

• Specular reflection (1) occurs on smooth
  surfaces and is often called mirror reflection.
  Specular reflection causes light to be reflected
  in a single direction at an angle equal to the
  angle of incidence.Diffuse reflection (2)
  occurs on rough surfaces and causes light to be
  reflected in several directions.

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Specular reflection
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Diffuse reflection
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Reflectance of Surfaces

• Most earth surface features lie somewhere between
  perfectly specular or perfectly diffuse
  reflectors.
• Whether a particular target reflects specularly
  or diffusely, or somewhere in between, depends on
  the surface roughness of the feature in
  comparison to the wavelength of the incoming
  radiation.
• If the wavelengths are much smaller than the
  surface variations or the particle sizes, diffuse
  reflection will dominate.

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The relationship between these three energy
interactions

• E i (l) E r (l) E a (l) E t (l)
• E i Incident energy
• E r Reflected energy
• E a Absorbed energy
• E t Transmitted energy

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Atmospheric Windows

• Because these gases absorb electromagnetic energy
  in specific wavebands, they strongly influence
  where we look spectrally with any given remote
  sensing system.
• The wavelength ranges in which the atmosphere is
  particularly Transmissive are referred to as
  atmospheric windows

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Atmospheric Windows

• Some sensors, especially those on meteorological
  satellites, seek to directly measure absorption
  phenomena such as those associated with CO2 and
  other gaseous molecules.
• Note that the atmosphere is nearly opaque to EM
  radiation in the mid and far IR
• In the microwave region, by contrast, most of the
  EM radiation moves through unimpeded - so that
  radar at commonly used wavelengths will nearly
  all reach the Earth surface unimpeded - although
  specific wavelengths are scattered by raindrops.

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Remote Sensing Principle Cont

• Energy Source or Illumination (A) - the first
  requirement for remote sensing is to have an
  energy source which illuminates or provides
  electromagnetic energy to the target of interest.
  
• Radiation and the Atmosphere (B) - as the energy
  travels from its source to the target, it will
  come in contact with and interact with the
  atmosphere it passes through. This interaction
  may take place a second time as the energy
  travels from the target to the sensor.
• Interaction with the Target (C) - once the energy
  makes its way to the target through the
  atmosphere, it interacts with the target
  depending on the properties of both the target
  and the radiation.
• Recording of Energy by the Sensor (D) - after the
  energy has been scattered by, or emitted from the
  target, we require a sensor (remote - not in
  contact with the target) to collect and record
  the electromagnetic radiation.
• Transmission, Reception, and Processing (E) - the
  energy recorded by the sensor has to be
  transmitted, often in electronic form, to a
  receiving and processing station where the data
  are processed into an image (hardcopy and/or
  digital).
• Interpretation and Analysis (F) - the processed
  image is interpreted, visually and/or digitally
  or electronically, to extract information about
  the target which was illuminated.
• Application (G) - the final element of the remote
  sensing process is achieved when we apply the
  information we have been able to extract from the
  imagery about the target in order to better
  understand it, reveal some new information, or
  assist in solving a particular problem.

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Remote Sensing Principle Cont

• Energy Source or Illumination (A) - the first
  requirement for remote sensing is to have an
  energy source which illuminates or provides
  electromagnetic energy to the target of interest.
  
• Radiation and the Atmosphere (B) - as the energy
  travels from its source to the target, it will
  come in contact with and interact with the
  atmosphere it passes through. This interaction
  may take place a second time as the energy
  travels from the target to the sensor.
• Interaction with the Target (C) - once the energy
  makes its way to the target through the
  atmosphere, it interacts with the target
  depending on the properties of both the target
  and the radiation.
• Recording of Energy by the Sensor (D) - after the
  energy has been scattered by, or emitted from the
  target, we require a sensor (remote - not in
  contact with the target) to collect and record
  the electromagnetic radiation.
• Transmission, Reception, and Processing (E) - the
  energy recorded by the sensor has to be
  transmitted, often in electronic form, to a
  receiving and processing station where the data
  are processed into an image (hardcopy and/or
  digital).
• Interpretation and Analysis (F) - the processed
  image is interpreted, visually and/or digitally
  or electronically, to extract information about
  the target which was illuminated.
• Application (G) - the final element of the remote
  sensing process is achieved when we apply the
  information we have been able to extract from the
  imagery about the target in order to better
  understand it, reveal some new information, or
  assist in solving a particular problem.

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The Remote Sensing Process

• Steps involved in the Process
• Identifying the problem
• Collection of data
• Analyze data
• Information output

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The Answer

• The most obvious source of electromagnetic
  energy and radiation is the sun. The sun provides
  the initial energy source for much of the remote
  sensing of the Earth surface. The remote sensing
  device that we humans use to detect radiation
  from the sun is our eyes. Yes, they can be
  considered remote sensors - and very good ones -
  as they detect the visible light from the sun,
  which allows us to see.

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How much have you learned?

• Assume the speed of light to be 3x108 m/s. If
  the frequency of an electromagnetic wave is
  500,000 GHz (GHz gigahertz 109 m/s), what is
  the wavelength of that radiation? Express your
  answer in micrometres (mm).

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The Answer

• Using the equation for the relationship between
  wavelength and frequency, let's calculate the
  wavelength of radiation of a frequency of 500,000
  GHz.
• Since micrometres (mm) are equal to 10-6 m, we
  divide this by
• 1x10-6 to get 0.6 mm as the answer. This
  happens to correspond
• to the wavelength of light that we see as
  the colour orange.

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• TAMAT