The claim: radar technology would not work if the earth were a sphere

An April 20 Instagram post (direct link, archived link) shows an image of a world map on a radar screen.

“You think radar works on a ball?” read the text in the post. “Think again.”

The post garnered more than 1,000 likes in four days.

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Our rating: Wrong

Scientists say the logic of the post is flawed and that radar technologies are to blame for the curvature of the earth. In addition, the curvature of the earth plays a role in some of the limitations of radar technology. A wealth of evidence shows the Earth is spherical – including images of the planet taken from space.

Scientists say radar technology is responsible for the curvature of the earth

Radar technology uses radio waves to detect and track objects in the atmosphere. Radar technology has a wide range of applications, including tracking weather and precipitation, monitoring the airspace for aircraft and air forces, tracking ships at sea, and calculating the speed of moving objects.

Radar consists of an antenna and a large rotating dish. As the dish rotates, the antenna emits beams of energy called radio waves into the atmosphere. The antenna can emit beams of energy at slightly different angles as it rotates and reaches a few degrees above and below the horizon line.

When the wave hits an object like a water droplet or an airplane, the beam of energy is scattered and reflects some of that energy back to the radar dish. The radar is able to calculate the size of the object and its distance by analyzing the strength of the reflected signal.

According to Jessica Schultz, associate director of the National Weather Service Radar Operations Center, radar technology takes beam angle and the curvature of the earth into account in its calculations to determine the location of detected objects.

Ground-based radars are usually pointed skyward to a small extent, depending on location and purpose. Especially with long-range weather radar, the radar beam gets taller the farther it gets from the radar location because of beam angle and the curvature of the earth, Schultz said.

The story goes on

As a result, weather radars can “overshoot” certain areas and have difficulty detecting near-surface precipitation at long ranges. Planes and other airborne objects can exploit this to evade detection by air traffic control and other radars, Doerry said, noting that this is the premise of the slang term “flying under the radar.”

Armin Doerry, a radar researcher at Sandia National Laboratories, confirmed this in a 2013 report on the effects of earth curvature and atmospheric refraction on radar signals.

“The earth is not flat and radar beams do not travel straight,” Doerry wrote. “This becomes more noticeable with increasing range.”

Both Schultz and Doerry told USA TODAY that because the atmosphere isn’t uniform in terms of density, humidity, or temperature, radar beams don’t travel in perfectly straight lines. In general, the atmosphere is less dense at higher altitudes, causing the radar beam to bend along the Earth’s surface.

According to the American Physical Society, the ancient Greeks were the first people to theorize that the earth could be naturally spherical. Modern scientists have uncovered ample evidence confirming this has been the case for thousands of years since.

For example, Polaris — also known as the North Star — would always be visible in the night sky if Earth were a flat plane, physicist Jason Steffen previously told USA TODAY. But that’s not the case, as people in the southern hemisphere can’t see the star, Steffen said.

USA TODAY has previously debunked a number of flat earth posts, including ones that claim a laser test proves the earth is flat and that Antarctica is really an ice wall and not a continent.

Summary of the fact check: Debunking the flawed science behind flat earth claims

USA TODAY reached out to the Instagram user who shared the post for comment, but received no immediate response.

Our sources:

• USA TODAY, December 7, 2022, Fact Check Summary: Debunking the Flawed Science Behind Flat Earth Claims

• USA TODAY, December 7, 2022, Fact Check: Laser beam tests conducted over water are distorted by refraction, do not prove the earth is flat

• USA TODAY, Nov. 17, 2022, Fact check: Plenty of evidence that the earth is round and spinning, contrary to persistent claims on social media

• American Physical Society, June 2006, This month in the history of physics

• Armin Doerry, April 27, phone interview with USA TODAY

• Bureau of Meteorology accessed May 5, How Radar Works

• Encyclopedia Brittanica, updated February 20, Radar

• Jessica Schultz, April 25, phone interview with USA TODAY

• KYFR, 20 July 2022, Morse code of the weather: limitations of weather radars including radar gap in far western ND and how to deal with it

• Laser Interferometer Gravitational-Wave Observatory, invoked March 23, Ultra-High Vacuum

• National Center for Atmospheric Research, accessed May 5 How Do Radars Work

• National Weather Service accessed May 5, NWS Radar: How does the radar work?

• National Weather Service accessed May 5, JetStream Max: Radar Beams

• NOAA, April 3, How Radar Works

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This article originally appeared on USA TODAY: No, radar technology doesn’t prove the earth is flat | fact check