Materials

1
Activity How Can radar See?

• Materials
• Polarized glasses (3-d movie glasses, or from
  Rainbow Symphony)

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Part 1 Electromagnetic Spectrum

• Radiation
• The emission of energy as electromagnetic waves
  or as moving subatomic particles
• Photon
• A particle representing a quantum of light or
  other electromagnetic radiation. A photon carries
  energy proportional to the radiation frequency
  but has zero rest mass

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• Frequency
• The rate at which something occurs or is repeated
  over a particular period of time or in a given
  sample.
• Amplitude
• The maximum extent of a vibration or oscillation,
  measured from the position of equilibrium

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Examples of instruments

• Radio
• FM/AM/Shortwave radio, etc.
• Microwaves
• Microwave ovens, Radar
• Infrared
• Heat, remote controls, etc.
• Visible
• Ultraviolet (UV)
• Produced by the sun, black lights
• X-ray
• Doctors office, etc.

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Discussion

• How are radar waves different from visible light
  waves?
• Radar waves
• have a longer wavelength larger distance between
  the crests of each wave
• lower frequency
• Visible light waves
• Wavelengths are much smaller
• Can be seen by the human eye

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Radar review

• What does radar stand for?
• Radio Detecting and Ranging
• What can we use it for?
• Because microwaves, such as radar, can penetrate
  haze, light rain, snow, clouds and smoke, these
  waves are good for viewing the Earth from space

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Part 2 Polarized Light

• Brainstorming
• Describe what you know about polarization
• Students may or may not know what polarization
  is.
• Take a few minutes to have students brainstorm
  what they think polarization is, and help them
  identify familiar objects that they may know
  (i.e. Polaroid camera, polarizing sunglasses).
• Remind them that at this point, they are just
  putting their ideas down on paper.

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Radar-Polarization connection

• Radar
• reflected off any surface
• determine certain aspects of a surface not
  visible
• Polarization /MiniRF Instrument
• radar energy
• measures the polarization of the radar energy as
  it is reflected off of a surface.

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Vocab

• Polarization is the term used to describe the way
  in which the electromagnetic wave oscillates as
  it travels along.
• Vertically polarized waves will oscillate up and
  down as it moves forward
• horizontally polarized waves will oscillate from
  side to side.

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Circular Polarization

• Other types of polarization are possible, for
  example circular polarization in which the wave
  oscillates in a circle as it moves along
• (Demo You can use a slinky, long spring, or
  rope to emphasize these points).

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Part 3 Polarizing Lenses

• Activitypart 1
• For the first part of this activity, you will
  need a set of polarizing filters.
• We will be using the polarizing glasses through a
  company called Rainbow Symphony.
• http//www.rainbowsymphony.com/3d-polarized-glasse
  s.html

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Procedure (5 min)

• Look through the lenses of one pair of glasses to
  see how they reduce the amount of light passing
  through.
• Describe what you see
• Next, use a second set of glasses, and put the
  lenses on top of each other and look through both
  together.
• Rotate one lens by 90 degrees and the light
  passing through the two screens should be zero
  (i.e. you should see nothing).
• Describe what you see
• Why does the lens go dark?

13
Both horizontal and vertical components of the
light have been screened out
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Polarizing Lenscont

• For the second part of this activity, you will
  need to go outside and look at the reflected
  light off of a car windshield, leaves, etc.
• Using polarized glasses you will observe 2
  things
• How light can be reflected to show stress or
  strain in windows
• How using a polarizer can affect the reflection
  of light off an object.
• Materials
• Polarized glasses

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Outside Activity (10 min)

• Before we begin looking at the reflected light
  from the car window, put the glasses on and look
  at the sky, trees or any other object.
• What do you see?
• Next, take the polarized glasses off and look at
  the windshield of a vehicle.
• Do you notice anything unusual? Describe what
  you see.
• Now put the polarized glasses on, while looking
  at the car windshield.
• What has changed?
• Do you notice any unusual patterns on the
  windows?
• Does it change when you look at the cars
  windshield through a window of another vehicle?
• Describe what you see

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Whats going on

• Light from the sky is reflected by the windshield
  of the other car at an angle, making it mostly
  horizontally polarized. The rear window is made
  of tempered glass.
• Stress in the glass, left from its heat
  treatment, causes it to alter the polarization of
  light passing through it.
• The stress in the rear window changes some of the
  horizontally polarized light into vertically
  polarized light that can pass through the
  glasses.
• As a result, the regular pattern of the heat
  treatment becomes visible

17
Using polarized lenses outside

• Polarizing filters, such as a pair of polarizing
  sunglasses, can be used to observe this effect by
  rotating the filter while looking through it at
  the reflection off of a distant horizontal
  surface.
• At certain rotation angles, the reflected light
  will be reduced or eliminated.

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Additional Activities

• Observe reflections elsewhere around you.
• Rotate the glasses and vary the angle of viewing
  to vary the brightness.
• Try looking at a reflection from a metallic
  surface, such as an ordinary mirror.
• Do you notice any difference?

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How does this relate to Mini-RF?

• This image is a Mini-RF synthetic aperture radar
  (SAR) strip overlain on an Earth-based, Arecibo
  Observatory radar telescope image.
• Mini RF
• transmits a microwave pulse (radar) to the
  surface
• circularly polarized radar signal (at microwave
  frequencies) and receives horizontally and
  vertically polarized returns.

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• This image describes how Mini RF receives this
  information from the ground track.
• By measuring the type of reflected polarized
  energy that comes back to the instrument,
  scientists can determine what lies just below the
  surface of the moon.