Discovering Radar and Polarized Light Connection

1. Activity —How Can radar See? • Materials • Polarized glasses (3-d movie glasses, or from Rainbow Symphony)

2. 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

3. 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

4. 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.

5. 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

6. Radar review 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 Mt. Pinatubo, the Philippines as seen from space. Clouds and vegetation obscure surface features • 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:

7. 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.

8. 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.

9. 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 polarizedwaves will oscillate from side to side.

10. 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).

11. 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-polarized-glasses.html

12. 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

14. 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: • 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

15. 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

16. 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

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.

19. 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?

20. 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.

21. 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.