Remote Sensing ' Lecture 5

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Lecture 5 Content

• Remote sensing platform examples

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• Platform examples
• Ground attached
• Used for special purposes involving very small
  low level vertical remote sensing surveys, for
  example
• Archeological diggings
• Spectral reflectance studies of growing crops
• Most convenient to attach to the ground
• These include towers, mobile cranes, hydraulic
  platforms, kites, balloons

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• Very inexpensive to buy or hire
• Have the advantage of exact positioning and being
  stationary during observations
• All such platforms can be manned
• Useful for also making low level oblique images
  and for stereo photography for architectural
  photogrammetry

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• Small airborne
• This includes platforms which are not as costly
  and limited as the survey aircrafts
• Drones
• Unmanned guided aircraft
• Used to fly over enemy lines in time of war
• Very small version model aircraft
• Helicopters
• More expensive than the typical survey aircraft
• Advantage of being able to hover stationary at
  any desired altitude
• Free flying balloons
• Oblique photography
• Lacks control over flight direction

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• Survey aircraft
• The following table give a general comparison of
  the main types of aircraft for aerial survey

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• The different types of survey aircraft suit
  different types of remote sensing missions
• The smaller ones are hired for short periods and
  within the operational limits
• Large aircrafts are typically not used to cover
  small areas, however, for flying blocks of
  photographs they are ideal

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• Earth orbiting
• Very costly instruments
• Imagery obtained from orbit
• Typically covers large areas because of high
  altitude
• Lower resolution than aircraft products
• Various platforms are considered based upon
  orbital altitude, inclination to the Earths
  axis, time spent in orbit, the types of sensors,
  manned or unmanned

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• American Space shuttle
• The challenger accident delayed the Shuttle
  program
• As a platform, the shuttle has several advantages
  over satellites
• For each mission the orbit can be different
• There is a crew to operate the sensors
• There is enough power to operate several sensors
• Shuttle mission a metric camera took about 1000
  photographs

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• Other manned satellites
• American satellites are Mercury, Gemini, Apollo,
  and Skylab
• Only Skylab provided images of real scientific
  importance
• In mid 1970s Skylab orbited at 435km and passed
  over each point on the earths surface between
  50 N and 50 S
• Contained a MSS, a microwave radiometer
• Took over 35,000 photographs of high quality

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• Unmanned earth resources satellites
• Satellites operated in near-polar sun synchronous
  orbits
• Other orbits are possible, eg. The
  near-equatorial orbit of the Tropical Earth
  Resources Satellite (TERS)
• All orbits are in the range 600 to 900 km and are
  so designed that the satellite can cover its
  designated part of the Earths surface
• Examples of unmanned satellites are
• Landsat and SPOT (discussed in next lecture)
• Satellites have passive sensors only powered by
  solar panels
• Camera photography is not used because of the
  problem of retrieving the film

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• Unmanned meteorological satellites
• Different orbiting requirements than the earth
  resources satellites
• Daily and more frequent coverage is required but
  not necessarily with high resolution
• Uses
• Medium altitude (500 to 15,000km) and near polar
  orbits
• OR
• Very high altitudes (at least 35,000km) and
  geostationary orbits

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• A typical near polar sun synchronous satellite
  does 14 to 15 orbits per day, passing each point
  on the Earths surface at the same time
• The swath width of the Advanced Very High
  Resolution Radiometer (AVHRR) is 3000km at an
  altitude of 830
• The geostationary satellites orbit above the
  Equator and have an orbiting period of 1 day
• Sensors record every 30 mins during the daytime

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• Military and experimental Earth observation
  satellites
• Not much is known about these satellites
• Orbits are varied, sometimes very low to get a
  close look
• Some can move around to change their orbits
• Some carry electro-optical scanners, while others
  carry frame cameras which ejects the film
  capsules for retrieval
• Main characteristic is their ability to acquire
  very high resolution images of small areas

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GOES Eastern US SECTOR IR Image
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http//www.fourmilab.ch/earthview/satellite.html
Sample list of satellites
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• The End