China launches first-ever geosynchronous orbit SAR satellite

Synthetic aperture radar satellites can image Earth during the day and night, even through adverse weather conditions.
Chris Young
A Long March 4C launch in 2021.
A Long March 4C launch in 2021.

Getty Images 

China launched the world's first geosynchronous orbit synthetic aperture radar (SAR) satellite aboard a Long March 3B rocket at 1:26 am Beijing time on Sunday, a report from the South China Morning Post reveals.

The rocket carrying the Ludi Tance 4-01 satellite launched from the Xichang launch center in the province of Sichuan and is gradually climbing to a geosynchronous orbit with an altitude of roughly 22,370 miles (36,000km).

China's world-first SAR satellite

The Ludi Tance 4-01 will continuously monitor the Asia-Pacific region at a resolution of approximately 65 feet (20 meters).

A geosynchronous orbit is a fixed orbit of a specific location on Earth. The satellite moves at practically the same speed as Earth's rotation, so it appears to be fixed.

In the case of Ludi Tance 4-01, translated to 'Land Exploration,' will continuously orbit over the same region and view a third of the entire Earth.

According to the China Aerospace Science and Technology Corporation (CASC), the satellite will provide "all-day, all-weather observation of China and surrounding areas."

Ludi Tance 4-01 will mainly be used for disaster prevention and relief, though it will also provide observations for oceanography, meteorology, agriculture, and forestry.

The benefit of SAR satellite technology

SAR satellites differ from the more conventional optical remote sensing satellites that capture images in the visible and near-infrared wavebands.

SAR technology sends energy pulses to Earth in the form of microwaves and then measures how long they take to bounce back to a sensor on the satellite. SAR signals are able to penetrate clouds, fog, and forestry and can image during the day and night.

Satellites using SAR imaging technologies have so far only been deployed in low Earth orbit, meaning Ludi Tance 4-01 will be the highest-altitude SAR satellite orbiting Earth.

According to CASC, the Ludi Tance 4-01 also works in the L-band, meaning it has a better capacity for penetrating forest regions as it has more interactions with large branches and tree trunks.

In an interview with the South China Morning Post, Stephen Hobbs, a professor in space systems and sensors at Cranfield University in the United Kingdom, said Ludi Tance 4-01's 20 meter (65 feet) spatial resolution is "good for geosynchronous radar."

"It should be able to observe subtle, millimeter-level ground motions due to landslides and earthquakes, which is a powerful measurement capability," he continued.

Just last week, Rocket Lab announced it would launch a satellite for Japanese space firm iQPS, which aims to send a constellation of SAR satellites to low Earth orbit. Much like China's Ludi Tance 4-01 satellite, the iQPS constellation will be utilized for disaster prevention, agriculture observation, and more.

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