Remote Sensing ' Lecture 7

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Lecture 7 Content

• Near Polar orbiting earth
• resources satellites
• SPOT
• LIDAR

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• SPOT
• LANDSAT system suffered three major drawbacks
• Very high ground resolution is not possible with
  the mechanical MSS used
• The repetition time for any one scene is quite
  long, 18 or 16 days per satellite. Satellites
  have limited operational value especially when
  data is needed for monitoring purposes.
• Stereoscopic viewing is only possible in narrow
  image overlaps, and the accuracy of height
  estimation is low

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• SPOT
• French tackled these drawbacks as follows
• It was decided to use a pushbroom scanner. Not
  only can modern pushbroom scanners provide high
  resolution, they have a longer and more reliable
  life expectancy, lower power requirements, and
  higher geometric and radiometric accuracy
• Mirrors make off-nadir viewing possible which
  allow any area to be viewed frequently. Oblique
  viewing allowed for stereoscopic viewing

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• SPOT satellite characteristics
• SPOT in the first earth resource satellite to be
  launched from Europe
• Other characteristics of SPOT which are similar
  to LANDSAT
• Near-polar sun synchronous orbit
• Transmission of data to ground stations with the
  possibility of on-board recording
• SPOT sensors can sense in high resolution (10m)
  panchromatic mode or lower resolution (20m)
  multispectral mode in 3 wavelengths

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• A single SPOT scene covers a geographical
• area of 60 x 60 km.
• Two alternative modes of imaging are possible
  using
• SPOT
• Panchromatic black and white, with a ground
• resolution of 10 m
• Multispectral colour, with 20 m ground
• resolution acquired simultaneously in 3 bands
  
• green, red and near infrared.

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• In a MSS it scans the scene from side to side and
  reflects radiation from the ground surface onto a
  detector
• This process is limited by the accuracy of the
  rotating mirror
• To overcome this problem a HRV (High Resolution
  Visible) scanner is used in SPOT. It does not
  have any moving parts, instead, it records each
  scan line at one go by means of a line of
  detectors one detector for each area sampled on
  the ground
• Detectors are controlled by a microchip and
  controls 1,728 detectors on SPOT

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• Comparison between pushbroom scanner and MSS

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• SPOT 1 and SPOT 2 available and launched in 1985
  and 1986 respectively
• SPOT 1 carry two identical pushbroom scanners
  which are called High Resolution Visible (HRV)
  scanners
• When in panchromatic mode all of the detectors
  are sampled with a spatial resolution of 10m
• Used for mapping scales of 1150,000 to 1100,000
• When in multispectral mode only half of the
  detectors are sampled with a spatial resolution
  of 20m
• Used for pollution monitoring to vegetation
  mapping

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SPOT ground receiving stations
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SPOT Panchromatic
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SPOT Multispectral
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• LIDAR
• Light Detection And Ranging (LIDAR)
• It is a radiometer system that uses a light beam
  in stead of a microwave radar beam (Radar) to
  obtain measurements of speed, altitude, direction
  and range of a target
• Lidars are used to precisely measure distances
  and properties of far-away objects
• Its operation is that a powerful laser transmits
  a short and intense pulse of light
• Very high spatial resolution, for example a DEM
  was created of a complete coverage of the
  Netherlands at a spatial resolution of 1 cm
  (Introduction to LIDAR, 1997).

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• Use of LIDAR for accurate determination of
  terrain elevations began in the late 1970s but
  their use was limited due to project
  cost-effectiveness
• One of the most successful early applications of
  LIDAR was in the determination of accurate water
  depths
• Modern LIDAR acquisition makes use of a rapidly
  pulsing (20,000 to 50,000 pulses/sec) laser and a
  highly accurate clock to measure time
• The principle of LIDAR is similar to that of
  RADAR
• Further details in lecture 10

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LIDAR image at ground zero NY
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• Lidar Applications
• Atmospheric science
• - dynamics measurements temperatures, winds,
  and waves- climate measurements clouds,
  aerosols, and water vapor- ozone measurements
  depletions and polar stratospheric clouds- high
  altitude trace metal measurements sodium and
  potassium- pollution monitoring
• Astronomy
• planetary surface relief mapping (eg lidar Mars
  maps by NASA)
• Topographic mapping
• erosion monitoring
• Bathymetry (under water mapping)
• harbor profiling for marine safety

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• Forest ground and canopy measurements
• used to assess forest growth and health
• Building and factory construction
• measurements allow for precise prefabrication,
  improving efficiency and reducing costs
• Mine shaft mapping
• allows cavern monitoring for worker safety
• Aircraft docking
• for safe aircraft maneuvering near airport
  terminals
• Automobile speed monitoring
• a replacement for hand-held radar guns

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• The End