Apparatus for producing adaptive pilot signals

A seismic prospecting system where the frequency and duration of vibratory signals are automatically adjusted to compensate for deleterious variations in soil transmissivity which distort the equivalent reflection pulses. The actual signals injected into the earth are monitored by a near-field detector and compared with a predetermined standard. When the energy of one frequency of the injected signal equals the standard, a new frequency signal is computed and injected until it likewise equals the standard. In like manner, frequencies and durations of remaining segments in the vibratory signal are continuously generated until the spectrum of the equivalent reflection pulse closely approximates the standard spectrum chosen to best delineate the geological objective of the seismic survey.