SAR (Synthetic Aperture Radar)

An active sensor that sends its own radar pulses and measures the echo. Works through clouds, day or night, because it doesn’t need sunlight.

Why it matters

SAR is the only way to reliably image during storms, at night, or through cloud cover — critical for floods, sea ice, deformation, and all-weather monitoring.

Where you’ll meet it

• Sentinel-1 (ESA) is the workhorse C-band SAR most people start with — its imagery is widely used for flood mapping because it sees right through storm clouds.
• NISAR, the NASA–ISRO SAR mission, carries L- and S-band radars built for measuring land and ice deformation across the whole globe.
• SAR pairs naturally with InSAR (its interferometric cousin) — the same radar images, compared over time, reveal millimeter-scale ground movement.

In plain terms

Like a bat using echolocation instead of eyes — it makes its own “light” (radio waves) and listens for the bounce-back.