The resolution of a radar image is a function of the band,the polarization , the sensor, and the platform from which the sensor operates. Unlike the human brain computers can record bands seperately and mix any combination you want to use later. If the space between to objects is smaller then the smallest wavelength in that band, no waves will pass between. The return signals will arrive simultaneously and the image will show a single surface. Microwaves are electromagnetic waves and so unlike seismic techniques and more like electro-resistivity , the electrochemical properties of materials need to be considered when analyzing radar imagery.
Water has a very high dielectric constant, so it has very strong return signal.
Sillica has a very low dielectric constant, as a resultloose sand is transparent to some radar bands. Carbon and lignen have strong signals in some bands making plant cover inpenetrable. So radar can be used to view subsurface structures, provided the correct surface conditions and bands are used. If both are used and both recorded seperately. Unfortunately, returns from objects oriented with the emitted pulse are often so strong other features get lost in the noise.