In this field, Radar and, in particular, SAR antennas (Synthetic Aperture Radar) are really becoming more and more interesting. A Radar antenna has the characteristic to acquire data almost everywhere and in every time, either with good or bad weather conditions and either with daylight or darkness on the observed area. As a matter of fact, the electromagnetic waves sent out from these antennas in some frequencies can pass the clouds through and, in some conditions, vegetation, ice or particularly dry sand as well. By this instrument, then, it is possible to observe what is under a dense rain vegetation or under the desert sand.
In some cases, finally, the Radar is the only mean the scientists have to observe some regions of the Earth surface particularly hard to reach.