Category: Radar (SAR)
SAR (Synthetic Aperture Radar)
SAR is an active radar sensor that works day or night and can see through clouds, measuring surface scattering rather than reflected sunlight.
Also known as: radar imagery, microwave radar
Expanded definition
Synthetic Aperture Radar (SAR) emits microwave pulses and measures the returned signal. Because it is active, SAR does not depend on sunlight, and clouds do not block it.
SAR images behave differently from optical images. Pixel values represent radar backscatter, which is influenced by surface roughness, moisture, vegetation structure, and geometry. Interpretation is less intuitive but can be very powerful for monitoring during cloudy seasons.
SAR comes with its own artifacts: speckle noise, geometric distortion, and strong dependence on incidence angle and polarization. Good SAR workflows explicitly account for these factors.
Related terms
Backscatter
Backscatter is the amount of radar signal returned to the sensor, influenced by roughness, moisture, and structure.
Polarization (VV, VH, HH, HV)
Polarization describes the transmit and receive orientation of radar waves; different polarizations respond to different surface properties.
Speckle
Speckle is a grainy noise pattern in SAR imagery caused by coherent interference, typically reduced by filtering or multi-looking.
Incidence Angle
Incidence angle is the angle between the radar beam and the surface; it affects SAR backscatter and comparability.