Radar subsurface sounders have been also designed to measure the surface characteristics and access the buried structures of different planets in the Solar System.
In the context of planetary missions, radars operating at extremely different frequencies have been used. The choice of the frequency is of the uppermost importance since it will drive the penetration depth. Moreover, because the bandwidth is limited by the central frequency, this choice will also set the range resolution (i.e. its ability to distinguish between two targets at different distances of the instrument). Radars designed to perform deep soundings of the subsurface must operate at low center frequencies and consequently have a poor vertical resolution.