What is SAR?
Synthetic Aperture Radar (SAR) is an active imaging radar system that creates high-resolution 2D or 3D images of the Earth's surface by coherently processing the echoes of thousands of radar pulses transmitted and received as the satellite moves along its orbit. The satellite's motion is used to synthesise a very large virtual antenna — the synthetic aperture — far longer than any physical antenna that could be placed on a spacecraft, enabling resolution of under 1 metre from orbit.
All-weather, day-night capability
Unlike optical cameras, SAR transmits its own microwave illumination and is completely independent of sunlight — it works identically in total darkness. More importantly, radar wavelengths (typically 3–25 cm) penetrate clouds, rain, haze, and smoke without significant attenuation. This makes SAR the sensor of choice for monitoring flooded areas obscured by cloud cover, tracking wildfire progression through smoke, and monitoring polar ice year-round. ESA's Sentinel-1 SAR mission delivers free, global, 10-metre resolution data with a 6-day repeat cycle.
What SAR reveals that optical sensors cannot
SAR is sensitive to surface roughness and the dielectric constant (moisture content) of materials, enabling applications impossible with optical sensors: detecting soil moisture, mapping subsurface archaeological features, measuring millimetre-scale ground deformation via InSAR (used to monitor volcanoes, landslides, subsidence over oil fields and urban areas), and penetrating dry sand to image buried structures.
Commercial SAR constellation players
ICEYE (Finland, 30+ satellites), Capella Space (USA), Umbra, Synspective (Japan), and iQPS are operating commercial SAR microsatellite constellations. ICEYE achieves sub-hourly revisit at any point on Earth with a growing fleet of sub-100 kg microsatellites, delivering same-day imagery for insurance, maritime domain awareness, and defence applications.