The last thirty years of environment monitoring witnessed a rapid development of the active remote sensing technology. Therefore, it is appropriate to consider this period as an advent of the active remote sensing. This paper offers a quick outline of the basics terms, approaches and typical applications of the technology which includes radar, synthetic aperture radar, synthetic aperture radar interferometry and methods which are derived from the synthetic aperture radar interferometry including the differential synthetic aperture radar interferometry and permanent scatterers. The polarimetric synthetic aperture radar interferometry and LiDAR were omitted from this review.

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