Morse Code of Weather: what’s inside a weather radar and how do they work to detect precipitation?

Published: Jun. 15, 2022 at 9:19 PM CDT
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BISMARCK, N.D. (KFYR) - Weather radars are one of meteorologists’ most valuable tools, but how exactly do they work to detect precipitation?

Radar is actually an acronym that stands for radio detection and ranging. There are 155 of them across the U.S., mostly co-located at National Weather Service offices, including one at the Bismarck NWS and one northeast of Minot.

“Radars are essentially transmitting energy. You can think about it like radio waves, and that starts down low in what we call the transmitter. That’s where that energy is generated, it’s sent up to the radar in what we call a waveguide, it really guides the radio waves up to the top of the radar.

And that’s where we have the other components of the radar then, where it’s sending out that signal, that energy. And then it listens as it rotates around, for that energy to be reflected back to the radar from whatever precipitation or clouds that it detects.

Then, it works in reverse. Back down through the waveguide, to the transmitter, turns that information, that data, into imagery that we can see on our apps, that we can visualize as meteorologists to help to detect weather and to predict weather,” said Chauncy Schultz, science and operations officer at the Bismarck National Weather Service.

In Bismarck, the radar tower is 65 feet tall and the radar dome itself is 39 feet tall. Inside is a 28-foot-wide metal dish that focuses the radio energy when it’s being sent out into the atmosphere and when the radar is listening for energy that is reflected back. It can determine how far away the precipitation is based on how long it takes for the energy to come back to the radar.

“The more intense the rain is, the more that energy is sort of attenuated as it comes back. And, so, we know from that how much energy comes back to the radar how intense the rainfall is, how large the hail is,” said Schultz.

Despite its size, the dish itself can be pushed fairly easily when the radar is not in use. When it is in operation, two large motors rotate the dish as well as tilt the dish at different angles to get a full three-dimensional, 360-degree picture of precipitation hundreds of miles from the radar site. In Bismarck, I’m Jacob Morse reporting for your news leader.

Tune in to First at Four next Wednesday to see the second part of our radar deep-dive series.

Some more facts about weather radars:

  • The transmitter is located in a building at the base of the radar and is called Klystron. The radio frequency energy it produces looks like sine waves.
  • The white rectangular tubes, known as waveguides, that carry the radio frequency waves from the transmitter 65 feet up to the radar have fairly smooth bends in them when they have to change direction so as to not interfere with the radio waves.
  • In front of the metal dish inside the radar dome (also called the radome), is the feedhorn where the waveguide carrying the radio frequency waves ends. This directs the radio waves toward the large dish, the dish focuses the energy and sends it out into the atmosphere. When the signal bounces off precipitation and is returned to the radar, the dish focuses the energy and it goes back to the feedhorn where is sent back down through the waveguide and to the transmitter for the energy to be interpreted into usable data.
  • The radome is made of fiberglass, which allows the radio frequency to pass through it unimpeded.

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