Activity —How Can radar See?
• Materials
– Polarized glasses (3-d
movie glasses, or from
Rainbow Symphony)
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
• 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
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.
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
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:
Mt. Pinatubo, the Philippines as
seen from space. Clouds and
vegetation obscure surface
features
Mt. Pinatubo, the Philippines
as seen with a radar
instrument. Radar sees
through the clouds and
vegetation. False colors revel
lava flows and mud flows
seen in orange
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.
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.
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.
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).
Part 3: Polarizing Lenses
• Activity—part 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-polarizedglasses.html
Procedure (5 min)
1. Look through the lenses of one pair of glasses to see how
they reduce the amount of light passing through.
– Describe what you see
2. Next, use a second set of glasses, and put the lenses on
top of each other and look through both together.
3. 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?
Both horizontal and
vertical components
of the light have been
screened out
Polarizing Lens—cont
• 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:
1.
2.
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
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 car’s windshield through a window of
another vehicle?
– Describe what you see
What’s 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
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.
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?
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.
• 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.