What is Echelon Effect in Acoustics?

Question

I need answers only with regard to acoustics (sound, physics) - advance thanks

Answer 1

The following details indicate echelon was more used for sattellite communication intelligence for enhancing sound levels.
More details are given below and the source also is shown:
It now appears that the system identified as ECHELON has been in existence for more than 20 years. The need for such a system was foreseen in the late 1960s, when NSA and GCHQ planned ILC satellite interception stations at Mowenstow and Yakima.
The key component of the system are local "Dictionary" computers, which store an extensive database on specified targets, including names, topics of interest, addresses, telephone numbers and other selection criteria. Incoming messages are compared to these criteria; if a match is found, the raw intelligence is forwarded automatically. Dictionary computers are tasked with many thousands of different collection requirements, described as "numbers" (four digit codes).
An important point about the new system is that before ECHELON, different countries and different stations knew what was being intercepted and to whom it was sent. Now, all but a fraction of the messages selected by Dictionary computers at remote sites are forwarded to NSA or other customers without being read locally.
VR