Synthetic aperture radar (SAR)
Also known as: SAR imaging, radar satellite imaging
Synthetic aperture radar (SAR) is an imaging technique where a radar on a moving satellite or aircraft sends microwave pulses to the ground and combines the echoes to act like a much larger antenna.
The result is a detailed image that doesn't need sunlight and sees through clouds and smoke. While SAR images look strange and grainy compared with photos, they can measure ground movement down to millimetres, which makes them invaluable for monitoring ice, floods, oil spills, and sinking land.
Synthetic aperture radar (SAR), explained at three levels
At home
Regular cameras need light and clear skies. Radar satellites send out their own signals and listen for the echo, so they can make pictures of the ground at night or through thick clouds.
At work
SAR lets organizations monitor floods, ice, ships, and oil spills reliably, because it isn't blocked by weather or darkness.
At home
As the satellite flies, it collects echoes from the same spot many times. A computer combines them as if the antenna were kilometres long, which gives a much sharper image than the small antenna could alone.
At work
SAR images show surface roughness and moisture rather than colour. Smooth water looks dark, while buildings and ships look bright. Common uses include ship detection, sea-ice charting, flood extent mapping, and deforestation monitoring.
At home
By comparing radar images taken at different times, scientists can see the ground rise or sink by just millimetres. In my opinion, that's one of the most impressive things any satellite does.
At work
Interferometric SAR (InSAR) measures phase differences to detect subsidence, landslides, volcano inflation, and infrastructure deformation. Polarimetric SAR helps classify surfaces. Processing is complex, involving speckle, geometric distortions like layover, and large data volumes.
Real-world examples
At home
Sophie read that a radar satellite had spotted her city's new transit tunnel route causing slight ground settlement, measured in millimetres, before any cracks appeared on the surface.
At work
Jerome works in Arctic shipping logistics. His team uses daily SAR-based sea-ice charts from the Canadian Ice Service to plan safe routes through the Northwest Passage, even during polar night.
How it compares
| feature | Synthetic aperture radar (SAR) | Optical satellite imaging |
|---|---|---|
| Light needed | No, provides its own signal | Yes, sunlight |
| Clouds | Sees through them | Blocked |
| Image appearance | Grainy, greyscale, hard to read | Like a photograph |
| Ground movement | Measures millimetres with InSAR | Limited |
Radar sees in any weather. Optical is easier for people to read.
For analysts
SAR is reliable when you need guaranteed monitoring regardless of weather. I'd budget for specialist analysis, though, because raw radar images are easy to misinterpret.
History & origin
Carl Wiley, an engineer at Goodyear Aircraft, came up with the core idea of synthetic aperture radar in 1951. The military developed airborne SAR through the 1950s and 1960s. NASA's Seasat, launched in 1978, carried the first civilian SAR in orbit, though it failed after about 100 days. Canada became a SAR leader with RADARSAT-1 in 1995, used for sea-ice mapping and ship detection, followed by RADARSAT-2 and the RADARSAT Constellation Mission. Europe's Sentinel-1 made SAR data free from 2014. More recently, startups such as ICEYE and Capella Space launched small SAR satellites, and the NASA-ISRO NISAR mission launched in July 2025. In my view, SAR is Canada's quiet space superpower, born from the practical need to watch a huge, cloudy, ice-covered country.