terrain reticle to see though terrian

Hi there
I have a question awaiting an answer http://answers.unity3d.com/questions/1209740/terrain-reticlesee-though-terrian.html.
however i thought that i would link it here in the forums as there is more traffic here.

quick overview
we have procedurally generated terrain using satellite data. what i want to do is make it look like the blur reticle in homeworld deserts of karahk.
we can have another procedurally drawn terrain that is just the coloured height map or features (underground lakes etc. i then want to be able to mouse click and hold to see the second terrain overlaid. this i believe can be achieved using two cameras one pointing at each terrain.
I have searched high and low and basically "help", I cant seem to get an example working in unity 5.3.4 of all the examples i have found.