SHARAD is a radar sounder on Mars Reconnaissance Orbiter. It pings the Martian surface with radio and times the echoes. The strongest reflection is from the surface, but in some places there are also reflections from subsurface layers. To verify the presence of subsurface layers, the SHARAD team performs a "clutter simulation" that shows what the radargram would look like if all the echoes were generated by surface topography. For this particular radargram, an impact crater located close to the ground track produces a false echo that looks like an underground dome in the radargram. However, there is also a subsurface echo in the radargram whose location is marked with blue arrows, and is not visible at the same depth in the clutter simulation, so is assumed to be from a subsurface reflector. In this region, the Utopia basin of Mars, the interpretation of the SHARAD data is that there are mesas standing 90 to 100 meters tall that are made primarily of water ice.