Radar remote sensing is a type of active remote Sensing which uses electromagnetic energy backscattered from ground targets to extract physical and dielectric behavior.
[1] It is different from passive remote sensing, the most common type, as the electromagnetic radiation (EMR) is produced by the emitters and they transmit radiation at radio wavelengths (i.e. from around 1 cm to several meters) and sensors use the measured return to infer properties of the Earth's surface.
radar remote sensing uses long-wavelength energy that penetrates through clouds and is sensitive to changes in vegetation physical structure.
Thus, it has advantage in its capability of all-hour and all-weather imaging.
Various satellite based sensors are using this kind of technology to produce Radar based remote sensing data (see RADARSAT, TerraSAR-X, Magellan).