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  1. 1. Radar Many in a series of McGourty-Rideout Productions
  2. 2. What is Radar? <ul><li>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. </li></ul><ul><li>It’s basically radio echo </li></ul>
  3. 3. RADAR RA dio D etection A nd R anging <ul><li>Radar observables: </li></ul><ul><ul><li>Target range </li></ul></ul><ul><ul><li>Target angles (azimuth & elevation) </li></ul></ul><ul><ul><li>Target size (radar cross section) </li></ul></ul><ul><ul><li>Target speed (Doppler) </li></ul></ul><ul><ul><li>Target features (imaging) </li></ul></ul>Antenna Transmitted Pulse Target Cross Section Propagation Reflected Pulse (“echo”)
  4. 4. Radar Frequencies
  5. 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. 6. The Range <ul><li>Distance from the radar </li></ul><ul><li>Measured from time delay between transmitted pulse and returned signal received </li></ul>
  7. 7. The Range <ul><li>Remember, in general v=d/t and d=vt </li></ul><ul><li>The range is just a distance </li></ul><ul><li>Since radio waves travel at the speed of light (v = c = 300,000 km/sec ) </li></ul><ul><ul><li> range = c • time/2 </li></ul></ul><ul><li>Why divided by 2? </li></ul>
  8. 8. The Range <ul><li>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! </li></ul>
  9. 9. Radar Range Measurement Transmitted Pulse Reflected Pulse Range Target <ul><li>Target range = </li></ul>c  2 where c = speed of light  = round trip time
  10. 10. Atmospheric Effects
  11. 11. <ul><li>Atmospheric attenuation </li></ul><ul><li>Reflection off of earth’s surface </li></ul><ul><li>Over-the-horizon diffraction </li></ul><ul><li>Atmospheric refraction </li></ul>Radar beams can be attenuated, reflected and bent by the environment
  12. 12. Radar <ul><li>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. </li></ul>
  13. 13. How Strong Is It? <ul><li>The strength of the received echo can also be measured </li></ul><ul><li>This will vary with the distance of the target, its size, its shape and its composition </li></ul>
  14. 14. Types and Uses of Radar <ul><li>Search radars scan a large area with pulses of short radio waves </li></ul><ul><li>Targeting radars use the same principle but scan a smaller area more often </li></ul><ul><li>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 </li></ul>
  15. 15. Types and Uses of Radar <ul><li>Mapping radar scans a large regions for remote sensing and geography applications </li></ul><ul><li>Wearable radar which is used to help the visually impaired </li></ul><ul><li>Air traffic control uses radar to reflect echoes off of aircraft </li></ul><ul><li>Weather radar uses radar to reflect echoes off of clouds </li></ul>
  16. 16. Types and Uses of Radar <ul><li>Weather radars use radio waves with horizontal, dual (horizontal and vertical), or circular polarization </li></ul><ul><li>Some weather radars use the Doppler effect to measure wind speeds </li></ul>
  17. 17. Incoherent Scatter Radar- A Radar Application <ul><li>Used to study the Earth's ionosphere and its interactions with the upper atmosphere, the magnetosphere, and the solar wind </li></ul>
  18. 18. Incoherent Scatter Echo <ul><li>Electrons in ionosphere are radar targets </li></ul><ul><li>These electrons can scatter radio waves </li></ul>
  19. 19. Radar Can Measure Pressure <ul><li>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 </li></ul>
  20. 20. Radar Can Measure Temperature <ul><li>Some electrons are moving due to heat - In this case the echo is scattered </li></ul><ul><li>The echo will contain a range of frequencies close to the transmitter frequency </li></ul><ul><li>As the temperature increases, the electrons move faster </li></ul><ul><li>So radar can act like a thermometer and measure the temperature of the ionosphere </li></ul>
  21. 21. Radar Can Measure Wind Speed <ul><li>When an electron is removed from an atom, the remaining charged atom is called an ion </li></ul><ul><li>The ion gas can have a different temperature from the electron gas </li></ul><ul><li>The electron/ion mixture is known as a plasma and is usually in motion (like our wind) </li></ul><ul><li>So incoherent scatter radar can also measure wind speed </li></ul>