On September 15th at 01:23 UTC, China had a rare sea launch of a Long March 11H carrying nine satellites to orbit.

According to Gunter’s Space Page, these nine satellites are the B and C series of the Jilin-1 Gaofen-03 constellation. (The one and only Jilin Gaofen-03A satellite was considered a prototype for these new satellites, and it was also carried to orbit from a sea-launched Long March 11 in May 2019.)

All nine are Earth observation satellites operating in the optical part of the spectrum and weigh about forty kilograms each. Assuming they are in a similar orbit to the prototype Gaofen-03A, they will orbit at an altitude of about 579 kilometers.

The B series consists of six satellites with pushbroom sensors that will provide panchromatic imagery with a resolution better than one meter and multispectral imagery with a resolution better than four meters. The swath width — that’s the remote sensing term for the width of an image — for both modes is more than 17 kilometers.

The C series consists of three satellites with video sensors that can provide color video images with a resolution better than 1.2 meters and a coverage area not less than 14.4 kilometers by 6 kilometers.

BONUS FACT: Jilin is the province in which they are made, and “gaofen” just means “high resolution.”

So, I mentioned that the Gaofen-03 satellites used pushbroom sensors.

There are a few different types of imaging sensors used on satellites. Two of them are whisk broom sensors and push broom sensors. Before we talk about pushbroom sensors, we need to talk about whisk broom sensors.

Whisk broom sensors have many moving bits, such as rotating mirrors, that scan back and forth across the swath of land being imaged as the satellite passes over it. They capture a series of pixels one at a time using a mirror that scans back and forth.

The Gaofen-03 Series B satellites, on the other hand, have pushbroom sensors, which means the sensor consists of a row of pixels that all take an image at the same time.

A good analogy for how a pushbroom sensor works is to think of a flatbed scanner. It captures a row of pixels, moves a bit, and then captures the next row of pixels until the whole page has been captured.  The sensor on the arm that scans the page as it moves along the length of the page is, in fact, a pushbroom sensor. 

For an airborne or space-borne pushbroom sensor, the airplane or satellite is the arm that moves across the face of the Earth with the sensor that captures one row at a time. This video shows how the Landsat 8 pushbroom sensor works, which is the same way the Gaofen-03 Series B sensors work.

Pushbroom sensors are used in favor of whiskbroom sensors because they have fewer fast-moving moving parts, meaning fewer things to break in space. As you saw in the first video, Landsat 7 had a whisk broom sensor. That sensor failed because one of the fast-moving bits broke. Its successor, Landsat 8, uses a pushbroom sensor because it is a more reliable technology.

Finally, here is a side-by-side comparison of how the two types of sensors capture imagery as they pass over a target.

More Information

Xinhua News article