Abstract: A method of seismic exploration, wherein one or more vibratory sources are employed to generate an input signal whose frequency varies as a function of time and wherein the signal is reflected and refracted to detector stations from subsurface beds, in which the sources are tested for signal accuracy with respect to a reference. The method includes generating at a first location a system reference signal having a pattern of predetermined phase and frequency characteristics and generating at a first source a vibrator control signal or a motion detector signal. The vibrator control signal or the motion detector signal is converted to constant amplitude so that the signal pattern is represented principally by phase and frequency. The system reference signal is correlated with the vibrator control signal or the motion detector signal to generate a cross-correlation function.