What is Doppler radar and how does it work? KSAT Explains

The technology dates back to the 1940′s.

Meteorologists and weather experts in South Texas rely heavily on Doppler radar technology, but how does it work? How can a giant soccer-ball-shaped tower, known as the radome, detect clouds hundreds of miles away and send them to a computer as rain?

In this episode of KSAT Explains, KSAT meteorologist Justin Horne visits the National Weather Service station in New Braunfels for answers, as well as the Bracken Bat cave, a common hotspot on radar images.

Doppler Radar’s Beginnings

In the early 1900′s, military ships and planes needed radar to avoid collisions in the fog, but the technology became a means of defense for the first time in World War II.

The Army Signal Corps coined the acronym RADAR, which stands for “radio detection and ranging.”

“In 1934, they conducted experiments on behalf of the United States Navy because the Navy was concerned again about maritime navigation,” said Rudy Purifacto, Senior Air Force Historian.

The radars eventually started being used to detect aircraft.

On December 7, 1941, the first major example of what radar could do took place.

“They spotted a flight of planes, they believed was a flight of planes, 136 nautical miles north of Oahu. Of course, it was the Japanese invasion fleet of Pearl Harbor,” said Purifacto.

Radars then really took off, and experiments all over the world began.

“Radar was a boon for air traffic controllers, it was also later developed for radio astronomy, and traffic cops now use it to check for speeders,” adds Purifacto.

It was detecting weather where radar proved to be most useful.

So, after wartime, some of the radars were donated to the Weather Bureau.

Today, there are 159 weather radars strategically placed throughout the U.S. and its territories.

Doppler Radar Today

Improvements are constantly being made to radar technology.

Image of Doppler radar at the National Weather Service in New Braunfels, TX. (2022) (ksat12)

“About 10 to 15 years ago, there was new technology that the Doppler radar has adapted called dual polarization,” said Matt Brady, Meteorologist with the National Weather Service.

Dual polarization means the radar scans horizontally and vertically through the atmosphere. This change has been a huge step forward in the world of meteorology.

It helps weather experts detect how strong a thunderstorm might be if a hail core is forming and monitor for possible rotation.

Matt Brady and his team at the National Weather Service in New Braunfels witnessed this advancement in technology this past March.

“It was a significant tornado. It was an EF-2,” said Brady.

KSAT Meteorologist Adam Caskey shows the radar image during what is later determined to be an EF-2 tornado in Guadalupe County on March 21st, 2022. (ksat12)

The NWS issued a tornado warning that day with the wording “tornado on the ground” without any eyewitness evidence.

The reason? They could see the debris field on the Doppler radar image.

Here in San Antonio, we utilize two Doppler radar stations. One near Brackettville and one in New Braunfels.

Inside The Radome

KSAT climbed almost 90 feet to get inside the “radome” for a better look at what makes these radar images possible.

Once inside the iconic “soccer ball” in the sky, we saw the giant dish that spins 360 degrees all day long.

“During calm air, during calm weather...it’s going much slower. During very violent weather, like tornadoes possibly, it’s really spinning fast, and it’s making cuts in the air very quickly. As fast as it physically can,” explains Tony Freund, Electronic Technician for the National Weather Service in New Braunfels.

It’s a giant piece of machinery, and if a human were to stand in the way of the emitting waves, which is strongly discouraged, the human would feel themselves start to heat up like a microwave.

The radar tilts up so it’s never aimed towards the ground or us, but instead through the varying parts of thunderstorms.

So How Does It Work?

Example of how radio waves are emitted from the Doppler radar. (ksat12)

In order to do all of these cool and potential life-saving things, the Doppler radar uses radio waves, shooting waves out of the dish at close to the speed of light.

The waves bounce off of objects in the atmosphere and then return to the giant dish inside the radome.

The energy is put out at high levels, but only a fraction of it actually makes it back to the dish.

The measurement works like sound waves and the Doppler effect, hence the name Doppler Radar.

A computer system then takes that data, converts it, and maps it to show the results.


Swarm of Mexican freetail bats at the Bracken Bat Cave in New Braunfels, TX. (ksat12)

Yes. Doppler radar can also detect movement, such as the bats at Bracken Bat Cave in New Braunfels.

“Bracken cave is home to the largest colony of bats in the world. We’re talking about 20 million Mexican free-tailed bats,” said Fran Hutchins, Director of Bat Conservation International’s Bracken Cave Preserve.

The bats can be seen on radar images during late summer evenings as the bats emerge for their nighttime flights.

”Right there at the cave, we call it a batnado. It’s literally a swirling vortex of bats there at the cave and then you can see them streaming away as a river of bats in the sky,” adds Hutchins.

The bats can also be seen returning early in the mornings.

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Find more like this on the KSAT Explains page.

About the Authors

Justin Horne is a meteorologist and reporter for KSAT 12 News. When severe weather rolls through, Justin will hop in the KSAT 12 Storm Chaser to safely bring you the latest weather conditions from across South Texas. On top of delivering an accurate forecast, Justin often reports on one of his favorite topics: Texas history.

Myra Arthur is passionate about San Antonio and sharing its stories. She graduated high school in the Alamo City and always wanted to anchor and report in her hometown. Myra anchors KSAT News at 6:00 p.m. and hosts and reports for the streaming show, KSAT Explains. She joined KSAT in 2012 after anchoring and reporting in Waco and Corpus Christi.

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