Transcript Slide 1

Surface Remote Sensing Basics
(in context of Electromagnetic Radiation)
Faiza Azam
7-02-07
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Outline
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Definition
Elements of Remote sensing
Sensors and Plaforms
Electromagnetic Radiation Spectrum
Classification of Remote sensing on the basis of
Electromagnetic spectrum.
• Some talk about Orbits.
• Conclusion
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Definiton:
The techniques for acquisition of information about the
features of earth (at different time scales), without any physical
contact using devices that use electromagnetic energy,
acoustic waves and force fields.
• Classified as Active or Passive.
Main Elements of remote sensing
1. A PLATFORM to hold the instrument.
2. A target OBJECT to be observed.
3. An instrument or SENSOR to observe the target .
4. Key element is INFORMATION (Data).
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REMOTE SENSING ELEMENTS
http://ccrs.nrcan.gc.ca/resource
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Reception,
and Processing
6574321 –-- Transmission,
Interpretation
and
analysis
Energy Source
orthe
Illumination
Application
Radiation
Interaction
Recording
and
of
with
energy
the
atmosphere
target
by sensor
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Sensors
Active and Passive sensing:
Active systems:• Remote sensing systems that provide their own energy source of
illumination.
• Measure amplitude as well as the phase of the reflected signal.
• Operated any time and cover wavelentghs not provided by sun.
http://ccrs.nrcan.gc.ca/resource
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Sensors
Active and Passive sensing:
Passive systems:• Remote sensing systems that measure naturally available energy
• Measure incoherent energy.
• For reflective energies, passive sensors can only be used when sun
is lluminating earth.
http://ccrs.nrcan.gc.ca/resource
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Platforms
Air borne platforms:
• Fixed wings aircrafts
• Used to collect detailed images (photographic).
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Satellite Platforms
• Remote sensing is conducted from space shuttle or
orbiting satellites.
• Provide repetitive coverage of earth‘s surface on
continuous basis.
Space Shuttle
Satellite
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Energy Spectrum
Wavelengths used in Remote Sensing
• Ultraviolet – 0.3 to 0.4 μm
• Visible – 0.4 to 0.7 μm
• Near Infrared – 0.7 to 1.3 μm
• Middle Infrared – 1.3 to 2.8 μm
• Thermal Infrared – 2.4 to14 μm
• Microwave – 1 mm to 1 m
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Electromagnetic Spectrum
Infomation about
Sun and stars
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Radio waves
• Wavelength range: < 1 cm – 10, 100 m.
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Transmit radio and t.v. signals.
• Radar imaging: Waves are transmitted from a
satellite or airplane antenna. The reflected waves
(brightness) is used to form an image of the ground
in complete darkness or through clouds because as
they can pass through clouds and dry desert sand.
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Microwaves
• Wavelengths range: approx. 1 mm (the thickness of
a pencil lead) - 30 cm (one foot).
• Emitted from the Earth, from objects such as cars
and planes, and from the atmosphere.
• Two types; Active (scatterometers, alimeters)or
Passive(Radiometers)
• Can be detected to give information, such as the
temperature of the object that emitted the
microwaves.
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Infrared
• Wavelengths range: approx. 0.7 to 300 µm
 NIR (0.7 - 1.5 µm) & SWIR (1.5 - 3 µm)  reflected IR, solar rad.
refleced from earth‘s surface.
 MWIR (3 - 8 µm) & LWIR (8 - 15 µm)  thermal infrared (heat).
• Can be detected to give information, such as reflectance
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Visible
• Wavelengths range: 400 - 700 nm
• Coincides with the wavelength of greatest intensity of sunlight
• great utility for the remote sensing of vegetation and for the
identification of different objects by their visible colors.
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Ultravoilet
• Wavelengths range: 0.3 µm - 3.0 nm.
• Emitted from the sun, most of it is blocked by ozone in the
upper atmosphere.
• Used extensively in astronomical observatories. Also
concerned with the measurement of ozone.
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Classification of Remote Sensing
with respect to Radiation
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Classification
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Orbits
Geostationary orbits
Satellites (geostationary), at altitudes of approximately 36,000
kilometres, revolve at speeds which match the rotation of the Earth
(so seem stationary).
Usage:
• Collect information continuously
over specific areas. (Weather and
communications satellites)
• Due to high altitude, some
satellites can monitor weather and
cloud patterns covering an entire
hemisphere of the Earth.
http://ccrs.nrcan.gc.ca/resource
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Orbits
Near Polar Orbits:
Platforms follow an orbit (north-south) which, in conjunction with the
Earth's rotation (west-east), Cover most of the Earth's surface. Most
such orbits are also sun-synchronous.
Usage:
Being sun synchronous, ensures
consistent illumination conditions
when acquiring images in a specific
season over successive years, or
over a particular area over a series
of days. So important for
monitoring changes
http://ccrs.nrcan.gc.ca/resource
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Orbits
Near Polar Orbits
In near polar orbits, satellite travels northern pole to the southern
pole. The paths at poles are called ascending and descending
passes, respectively.
For sun-synchronous orbit:
Ascending pass
shadowed side of the Earth
Descending pass
sunlit side of the Earth
http://ccrs.nrcan.gc.ca/resource
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Conclusion
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What is remote sensing in general.
Main elements of remote sensing
Sensors, platforms
Electromanetic spectrum
(used for remote sensing)
• Classified remote sensing in terms of
wavelengths.
• Orbits
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Future of Remote Sensing
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