backscatter

Backscatter is the signal, which was reflected from the surface back to the direction where it came from.

Regarding Synthetic Aperture Radar (SAR) systems, backscatter for a target area at a particular wavelength will vary for a variety of conditions, such as the physical size of the scatterers in the target area, the target's electrical properties and the moisture content, with wetter objects appearing bright, and drier targets appearing dark (The exception to this is a smooth body of water, which will act as a flat surface and reflect incoming pulses away from the sensor. These bodies will appear dark). Read more: ESA SAR Tutorial