English to Slovak Science Aerospace / Aviation / Space radar technology

"All three of these activities can be accomplished using two things you may be familiar with from everyday life: echo and Doppler shift. These two concepts are easy to understand in the realm of sound because your ears hear echo and Doppler shift every day. Radar makes use of the same techniques using radio waves."

Source:
http://science.howstuffworks.com/radar.htm

I am native Slovak, fan of English. I use Lingea dictionary, I managed to find there an explanation in English what it is, but there is no slovak equivalent, and that is what I am looking for.

According english explanation by Lingea:
Doppler shift is a change in the apparent frequency of a wave as observer and source move toward or away from each other.