A correlator realized the function of the cross-correlation for the accurate determination of the time lag between two signals. Possible characteristics are special-purpose computer, analog circuits, brain structures or computer programs. The signals may be technically coded radio signals, radar, sonar or optical signals or echoes of natural origin.
The principle is explained using the example of three different applications,
- One direction measurement: measurement of the Earth's rotation by VLBI interferometry quasars,
- The velocity measurement by a moving direction staggered sensor pair, and
- A distance measurement: locating with the satellites of the Global Positioning System ( GPS).
In correlating two signals are shifted from each other as long calculation, to the characteristic of the two signals match. The shift is found then the time difference
- Either between the terms of a radiation source ( quasar ) to two ground stations
- And the signals of the two sensors which move successively across a structure
- Or between the signal received from a satellite and the receiver calculated in the code.
As long as the radiolocation receiver knows only very roughly in the room after turning on the orbits of the satellites and its own ( positionsabhängige! ) movement, his correlators must not only move because of the Doppler shift of the signals in time, but also stretch different. This two-dimensional search is considerably more complex.