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Radar

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  • Transcript

    • 1. Radar Many in a series of McGourty-Rideout Productions
    • 2. What is Radar?
      • RADAR (Radio Detection And Ranging) is a way to detect and study far off targets by transmitting a radio pulse in the direction of the target and observing the reflection of the wave.
      • It’s basically radio echo
    • 3. RADAR RA dio D etection A nd R anging
      • Radar observables:
        • Target range
        • Target angles (azimuth & elevation)
        • Target size (radar cross section)
        • Target speed (Doppler)
        • Target features (imaging)
      Antenna Transmitted Pulse Target Cross Section Propagation Reflected Pulse (“echo”)
    • 4. Radar Frequencies
    • 5. Radar Frequency Bands Frequency Wavelength 1 mm 1 km 1 m 1 nm 1 MHz 1 GHz IR UV 10 9 Hz 0 1 2 3 4 5 6 7 8 9 10 11 12 30 20 10 8 6 5 4 3 9 7 Allocated Frequency (GHz) Wavelength (cm) X-Band C-Band S-Band L-Band UHF VHF Visible 10 12 Hz Ku K Ka W 1  m
    • 6. The Range
      • Distance from the radar
      • Measured from time delay between transmitted pulse and returned signal received
    • 7. The Range
      • Remember, in general v=d/t and d=vt
      • The range is just a distance
      • Since radio waves travel at the speed of light (v = c = 300,000 km/sec )
        • range = c • time/2
      • Why divided by 2?
    • 8. The Range
      • The “2” is because the measured time is for a round trip to and from the target. To determine the range, you only want the time to the object, so you take half!
    • 9. Radar Range Measurement Transmitted Pulse Reflected Pulse Range Target
      • Target range =
      c  2 where c = speed of light  = round trip time
    • 10. Atmospheric Effects
    • 11.
      • Atmospheric attenuation
      • Reflection off of earth’s surface
      • Over-the-horizon diffraction
      • Atmospheric refraction
      Radar beams can be attenuated, reflected and bent by the environment
    • 12. Radar
      • The range and the direction of the target determine its location, which is what is needed for many radar applications such as air traffic control.
    • 13. How Strong Is It?
      • The strength of the received echo can also be measured
      • This will vary with the distance of the target, its size, its shape and its composition
    • 14. Types and Uses of Radar
      • Search radars scan a large area with pulses of short radio waves
      • Targeting radars use the same principle but scan a smaller area more often
      • Navigational radars are like search radar, but use short waves that reflect off hard surfaces. They are used on commercial ships and long-distance commercial aircraft
    • 15. Types and Uses of Radar
      • Mapping radar scans a large regions for remote sensing and geography applications
      • Wearable radar which is used to help the visually impaired
      • Air traffic control uses radar to reflect echoes off of aircraft
      • Weather radar uses radar to reflect echoes off of clouds
    • 16. Types and Uses of Radar
      • Weather radars use radio waves with horizontal, dual (horizontal and vertical), or circular polarization
      • Some weather radars use the Doppler effect to measure wind speeds
    • 17. Incoherent Scatter Radar- A Radar Application
      • Used to study the Earth's ionosphere and its interactions with the upper atmosphere, the magnetosphere, and the solar wind
    • 18. Incoherent Scatter Echo
      • Electrons in ionosphere are radar targets
      • These electrons can scatter radio waves
    • 19. Radar Can Measure Pressure
      • The strength of the echo received from the ionosphere measures the number of electrons able to scatter radio waves or what we call electron pressure
    • 20. Radar Can Measure Temperature
      • Some electrons are moving due to heat - In this case the echo is scattered
      • The echo will contain a range of frequencies close to the transmitter frequency
      • As the temperature increases, the electrons move faster
      • So radar can act like a thermometer and measure the temperature of the ionosphere
    • 21. Radar Can Measure Wind Speed
      • When an electron is removed from an atom, the remaining charged atom is called an ion
      • The ion gas can have a different temperature from the electron gas
      • The electron/ion mixture is known as a plasma and is usually in motion (like our wind)
      • So incoherent scatter radar can also measure wind speed
    • 22.