In the BBC News article Europe's Mars rover takes shape there is a short video describing the Structural and Thermal Model (STM) of the ExoMars Rover.
After describing the drill box, the narrator in the video says (approximate transcription):
But because you’ve got a drill, we’ve also need to be seeing where we are going to be drilling and to do that we’ve at the back here got ground penetrating radar.
So this is our ground penetrating radar bracket. There are two of them so you can see in stereo like you have two eyes, you get the depth perception.
And with those we can look at the structure of the rock for example in the ground and see where there would be a scientifically valid point to do that drilling so where there is a fissure between two different seams of rocks where there might be a life form protected from the harsh radiation at the surface might still be thriving today. (emphasis added)
We have two eyes because one eye has very little ability to sense depth, although there are optical imaging devices that can recover depth information such as Lytro's "light field" technology, and more interestingly REAL3™ depth-sensing imager chips which actually measures the photon time of flight on a per-pixel basis.
But radar, or RAdio Detection And Ranging certainly is sensitive to range and ground penetrating radar will provide reflected intensities as each depth.
So why are two ground-penetrating radar "eyes" necessary or important for the ExoMars Rover?