There is a word for the optical shimmering effect that is caused by heat. It is particularly noticible when you are lying on the ground looking into the distance (the effect, not the word). It is a long word of the following structure: ------(t?)(a?)tion, (I don't know how many letters.)
The answer is not mirage. It is a similar phenomenon, but not exactly the same. Could anyone remind me what it is as I was taught this at school and have forgotten.