The RADAR (RAdio Detection And Ranging) is an active microwave sensor widely used in the civil sector of large infrastructures and in the environmental monitoring and natural risk detection sector.

A radar measures distances and from their processing it is able to extract information about the vibrational frequencies of infrastructures.

Furthermore, modern radars, known as Synthetic Aperture Radars (SAR), allow us to obtain high quality images of the Earth’s surface.

A SAR radar sensor can be on board a satellite or installed on the ground using a track to allow the radar antennas to move along it.

The system parameters of a SAR sensor which require to be suitably chosen in monitoring applications are wavelength, polarization and angle of incidence.

The typical wavelengths used are of 1 cm (KU band) in ground based SAR sensors and of 3 cm (X band), 6 cm (C band), 24 cm (L band) in satellite sensors.

In the case of satellite SAR, the sensor passes over the area to be monitored, moving along its orbit and sending a sequence of microwave pulses toward the scene to be observed with a Pulse Repetition Frequency (PRF) and illuminating it for a fraction of a second.

In the case of ground-based SAR the antennas advance along a track of variable length from 1 to 4 meters, depending on the application and illuminating the scene for a few minutes.

In both cases, the processing of the returning echoes allows to obtain images of the scene with a spatial resolution of the order of a meter.