Introduction to Remote Sensing

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Introduction to Remote Sensing

• Guido Cervone

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Remote Sensing

• Remote Sensing is the technology that is now the
  principal modus operandi (tool) by which the
  Earth's surface and atmosphere, the planets, and
  the entire Universe are being observed, measured,
  and interpreted from such vantage points as the
  terrestrial surface, earth-orbit, and outer
  space.
• More generally
• Acquire data without being in contact with it

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Examples of Remote Sensing Data
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Examples of Remote Sensing Data
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Examples of Remote Sensing Data
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Early Applications of Remote Sensing

• At the beginning of the 20th century a Bavarian
  pigeon fleet that operated in Europe.

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Early Applications of Remote Sensing

• In 1906 an ingenious effort by "flying" cameras
  on kites to study the damage in San Francisco,
  right after the catastrophic earthquake
• Here is the resulting composite photo

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Early Applications of Remote Sensing

• Remote Sensing became a reliable instrument as
  humans learned how to fly

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Early Applications of Remote Sensing

• The logical entry of remote sensors into space on
  a routine basis began with automated photo-camera
  systems mounted on captured German V-2 rockets,
  launched out of White Sands, NM
• These rockets also carried geophysical
  instruments in their nose cones, which were
  returned to Earth by parachute

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Early Applications of Remote Sensing

• The modern Space program is held by many
  historians to truly have begun with the launch of
  Sputnik I by the Soviets on October 4, 1957

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Todays Remote Sensing

• Remote sensing technology is very advanced
• We can observe the Earth and its environment with
  a large array of instruments with very high
  spatial, spectral and temporal resolution
• Such observations give us unprecedented access to
  massive amount of data

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Space Countries

• Since the 1950s several countries have been
  sending satellites into space
• At first, the USA and the Soviet Union were the
  only countries capable of launching satellites
  into orbit
• Nowadays many countries have capabilities to
  launch satellites into orbit
• Satellites use was primarily military
• Reconnaissance
• Communication

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Space Countries

• Nowadays several countries can independently send
  satellites into space
• Applications are both Military and Civilian
• Reconnaissance
• Communication
• Navigation
• What else?

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Space Countries
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Earths Gravitational Pull

• The Earth's gravity pulls everything toward the
  Earth. In order to orbit the Earth, the velocity
  of a body must be great enough to overcome the
  downward force of gravity
• One important fact to remember is that orbits
  within the Earth's atmosphere do not really
  exist. Atmospheric friction caused by the
  molecules of air (causing a frictional heating
  effect) will slow any object that could try to
  attain orbital velocity within the atmosphere.
• In space, with virtually no atmosphere to cause
  friction satellites can travel at velocities
  strong enough to counteract the downward pull of
  Earth's gravity
• The satellite is said to orbit around the Earth

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Orbits

• Orbit refers to the path of a smaller object
  (secondary) around a bigger object (primary) as a
  result of the combined effects of inertia and
  gravity.

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Satellite Orbit

• One of the most important aspect of a satellite
  orbit is its inclination
• The inclination limits the types of coverage and
  data that a satellite can acquire
• The velocity of the satellites determines the
  height above the geoid

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Satellites Orbit
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Geosyncronous Satellites

• GEO are circular orbits around the Earth having a
  period of 24 hours.
• A geosynchronous orbit with an inclination of
  zero degrees is called a geostationary orbit.
• A spacecraft in a geostationary orbit appears to
  hang motionless above one position on the Earth's
  equator. For this reason, they are ideal for some
  types of communication and meteorological
  satellites.
• A spacecraft in an inclined geosynchronous orbit
  will appear to follow a regular figure-8 pattern
  in the sky once every orbit.
• To attain geosynchronous orbit, a spacecraft is
  first launched into an elliptical orbit with an
  apogee of 35,786 km (22,236 miles) called a
  geosynchronous transfer orbit (GTO). The orbit is
  then circularized by firing the spacecraft's
  engine at apogee.

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Typical Geostationary Coverage
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Metereological Satellites
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World Clouds
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Polar Orbits

• PO are orbits with an inclination of 90 degrees.
• Polar orbits are useful for satellites that carry
  out mapping and/or surveillance operations
  because as the planet rotates the spacecraft has
  access to virtually every point on the planet's
  surface
• Most PO are circular to slightly elliptical at
  distances ranging from 700 to 1700 km (435 - 1056
  mi) from the geoid.
• At different altitudes they travel at different
  speeds.

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(Near) Polar Orbiting Satellites
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Ascending Vs. Descending
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Daily Coverage
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Polar Regions

• The satellite doesn't pass directly over the pole
  due to the slight inclination of the orbital
  plane.
• The transparent overlay identifies the 3000 km
  wide swath that is viewed by the AVHRR imaging
  instrument on the satellite.
• The yellow curves delineate the limits of the 60
  degree viewing arcs from the six "standard"
  geostationary satellites included in these
  discussions.

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Sun Synchronous Orbits

• SSO are near polar orbits where a satellite
  crosses periapsis at about the same local time
  every orbit.
• This is useful if a satellite is carrying
  instruments which depend on a certain angle of
  solar illumination on the planet's surface.
• In order to maintain an exact synchronous timing,
  it may be necessary to conduct occasional
  propulsive maneuvers to adjust the orbit.
• Most research satellites are in Sun Syncronous
  Orbits
• There is a special kind of sun-synchronous orbit
  called a dawn-to-dusk orbit. In a dawn-to-dusk
  orbit, the satellite trails the Earth's shadow
  (Why do you think this could be convinient?)

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Molniya Orbits

• They are highly eccentric Earth orbits with
  periods of approximately 12 hours (2 revolutions
  per day).
• The orbital inclination is chosen so the rate of
  change of perigee is zero, thus both apogee and
  perigee can be maintained over fixed latitudes.
• This condition occurs at inclinations of 63.4
  degrees and 116.6 degrees. For these orbits the
  argument of perigee is typically placed in the
  southern hemisphere, so the satellite remains
  above the northern hemisphere near apogee for
  approximately 11 hours per orbit. This
  orientation can provide good ground coverage at
  high northern latitudes.

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Molniya Orbits
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Tundra Orbits

• Tundra orbit is a class of a highly elliptic
  orbit with inclination of 63.4 and orbital
  period of one sidereal day (almost 24 hours).
• A satellite placed in this orbit spends most of
  its time over a designated area of the earth, a
  phenomenon known as apogee dwell.

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Different Orbital Distances
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Satellite Constellation

• A group of electronic satellites working in
  concert is known as a satellite constellation.
• Such a constellation can be considered to be a
  number of satellites with coordinated ground
  coverage, operating together under shared
  control, synchronised so that they overlap well
  in coverage and complement rather than interfere
  with other satellites' coverage.

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Satellite Formation
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Remote Sensing and Aviation

• How can we use the data from past, current and
  future satellite missions?
• Atmospheric chemistry
• Cloud physics
• Turbulence
• Volcanic Ash
• Mesoscale modeling
• Transport and Dispersion modeling