On March 30 at 22:45 UTC, a Chinese Long March 4C launched the Gaofen 12-02 spacecraft into orbit from the Jiuquan Satellite Launch Center in Northern China.

Gaofen 12-02 is the second in a series of high-resolution Earth observation satellites. The satellite has a synthetic aperture radar (SAR) sensor with sub-meter resolution. This means the smallest object the sensor can image is less than one meter by one meter in size. Like other satellites in the civilian China High-resolution Earth Observation System, or CHEOS, it will be used for land censuses, urban planning, land rights, road network design, crop estimation, disaster prevention and mitigation, and other fields.,

Radar satellites have different properties than optical satellites, and they complement each other. An optical satellite is like a camera; it can only see illuminated targets and capture reflected photons. If the target is obscured by clouds, an optical satellite can’t see it. Radar satellites emit a signal and record the reflection, which allows them to gather data day and night. Radar satellites use longer wavelengths on the electromagnetic spectrum that penetrate clouds, allowing for all-weather use.

If you were to take two images of a particular Russian volcano that was active in 1996, one with optical and one with SAR, you’d notice a few differences.

One of the major differences between the two images of this Russian volcano is that the surface details are more evident in the synthetic aperture radar image than they are in the photograph. The colors in the SAR image are a result of the processing, in which different colors were assigned to represent different textures and materials. Based on what can be seen, it appears that reds were assigned to areas where there was snow on the slopes of the volcanoes, while light blues were assigned to the areas that were clear of snow. It also makes it much more obvious that there are actually several volcanoes in the area, though only one appears to be erupting.

Another application of synthetic aperture radar imagery is to map sea ice in the extreme north. Different types of ice appear quite different in SAR imagery, making it relatively easy to produce maps that can help guide ships through the ice and avoid patches where even ice breakers will have problems.

More Information

CASC press release (Chinese)

China launches second Gaofen-12 Earth observation satellite (SpaceNews)

Gaofen 12 info page (Gunter’s Space Page)

Microwave remote sensing (Government of Canada)

Kliuchevskoi Volcano optical/radar comparison (Michigan Tech)

Launch video