Optical satellites capture reflected sunlight (so they need daylight and clear skies), while SAR (synthetic aperture radar) satellites actively illuminate the ground with radar and can image day or night and through clouds.
SAR is the right choice when timeliness must beat weather: floods, storms, and night events where cloud cover would block an optical sensor. SAR measures surface structure and moisture rather than colour, and is widely used for flood mapping, maritime surveillance, ground deformation (interferometry), and all-weather monitoring.
Optical imagery is the right choice when you need natural-colour or multispectral interpretation — vegetation health, visual damage assessment, land cover — and conditions allow a clear, daylight pass. Cloud forecasting and climatology are central to planning optical acquisitions.
Yes. SAR uses radar wavelengths that penetrate cloud and operate without sunlight, so SAR can image day or night and in any weather, unlike optical sensors.
SAR is usually preferred for floods because events are often accompanied by cloud and may occur at night, conditions under which optical sensors cannot collect usable imagery.
Plan a real acquisition over your area on the interactive map, browse the satellite catalog, or read the tasking guides.