Modified Transcript: Most radar is done by sending the signal through the air. We're sending it through the ice and that means we can not assume that the radar beam is going to do exactly what we as humans expect it to do, i.e., go straight to the object and reflect straight back at us. If you have ever reached your hand down into a pool of water or an aquarium, you can see your arm seems to bend and if you reach really quickly for an object you won't grab it. This is because of refraction, or the bending of light rays. The light doesn't travel straight to the object, it actually starts at one point and then gets refracted down to another point.
The refraction of radar in the polar ice sheet is actually more complicated than the refraction of light in water. In polar ice there is not a single point of refraction; It is actually a little bit of refraction at this point, then a little more as it goes deeper, then still a little more at another point lower down, etc. The radar signal sort of bends several times as it travels through ice layers that are of different composition. That adds quite a few problems when you're trying to model the behavior of the radar in ice, because it is difficult to define exactly how distorted the final signal will be and where the refraction will occur.