Doppler Radar

Doppler radar display
Doppler Weather Radar – NOAA

Let this Doppler Radar measure the speed of you throw

  • Throw a ball at the target behind the screen. The Doppler Radar box will flash red number which is the speed in miles-per-hour of your pitch.
  • How fast can you throw the ball?
  • How slow can you throw the ball?

The black box behind the screen is a Doppler radar machine which sens out a high frequency pulse ?. That is reflected off the moving ball. The moving ball compresses the signal slightly which changes the frequency of the pulse. The Doppler radar machine can measure the change in frequency an calculate the speed of the ball.

Hurricane Katrina Doppler

This is the same way police can measure the speed of a car on the highway and how Doppler radar can measure the speed of a moving storm.

  • Frequency modulation – One form of distance measuring radar is based on frequency modulation. Frequency comparison between two signals is an accurate method of measurement. By changing the frequency of the returned signal and comparing that with the original, the difference can be easily measured.
  • Speed measurement – Speed is the change in distance to an object with respect to time. The existing system for measuring distance, combined with a memory capacity to see where the target last was, is enough to measure speed.
  • |Doppler effect – if the transmitter’s output is coherent (phase synchronized), there is another effect that can be used to make almost instant speed measurements (no memory is required), known as the Doppler effect. Most modern radar systems use this principle in the pulse-doppler radar system. Return signals from targets are shifted away from this base frequency via the Doppler effect enabling the calculation of the speed of the object relative to the radar. The Doppler effect is only able to determine the relative speed of the target along the line of sight from the radar to the target.

What’s the problem?
Make an exhibit to demonstrate how Doppler radar can be used to measure the speed someone throws a ball.

  • Ask – Is the exhibit indoors? How much space is needed to track and measure the speed of a ball being thrown? Is there a Doppler radar measuring unit available that would be suitable for this application?
  • Imagine – What sort of structure is needed to keep the balls in the exhibit area? Where does the Doppler measurement unit need to be placed to record the throws?
  • Design, Build – The structure is built as a large cage from tubular metal pipe and open netting. The Doppler measurement unit is mounted on the rear wall of the exhibit just off to the right side of the target. The floor of the cage slopes down toward the front where the thrower stands so that the balls will roll back to the front for easy pick up.
  • Improve – the cage is large enough to be surly. The Doppler measurement is outside the cage structure. So it won’t be hit when the balls are thrown.

That’s engineering
Doppler effect
Engineering ideas

  • frequency, compression, measurement, calculate, slope, modulation, distance, speed, Doppler effect

Learn more…

Developed by the GE Volunteers in partnership with the Museum of Arts and Sciences (MOAS) – Daytona Beach, FL