The invention concerns a method and apparatus for detecting Doppler-shifted waveforms in electrical signals. A replica is derived from the waveform prior to Doppler shift and stored in a storage device as a non-uniform profile having progressively increasing distortion along its length. The replica storage device is connected non-uniformly to correlating means such that the correlated replica profile has a degree of uniform distortion varying with storage position simulating varying degrees of Doppler shift. The electrical signal is uniformly correlated with the replica while the replica storage position is varied. An output signal is generated indicating correlation variation. The electrical signal is repetitively sampled and a maximum correlation is detected when the waveform occurs in the electrical signal with a degree of Doppler shift matching that simmulated by the correlated replica. The invention also includes apparatus for performing the method.