Operational control in a seismic source

A method for controlling trajectory in a resonant marine seismic source comprises: controlling the source frequency and controlling the motion trajectory. Controlling the source frequency includes: estimating the source frequency from its internal state and the state of its environment; deriving a frequency error as the difference between the estimated frequency and the frequency of the desired trajectory; and driving the frequency error to zero. Controlling the motion trajectory includes: detecting a motion trajectory of the source; deriving a motion trajectory error as the difference between the desired motion trajectory and detected motion trajectory; and driving the motion trajectory error to zero.