Image Number 2 for United States Patent #5410517.
A method for cascading or linking seismic vibrator sweeps to form a cascaded sweep sequence. According to the method, a first cascaded sweep sequence is generated containing N sweep segments linked end-to-end. The N sweep segments are substantially identical, except that the initial phase angle of each sweep segment within the sweep sequence is progressively rotated by a constant phase increment of about 360/N degrees. A second cascaded sweep sequence is generated consisting of (i) N consecutive sweep segments linked end-to-end which correspond to said first cascaded sweep sequence and (ii) an additional sweep segment linked to the N consecutive sweep segments which is positioned and phased so as to substantially suppress harmonic ghosts during correlation. One of these cascaded sweep sequences is used for the vibrator sweep sequence and the other is used for the correlation reference sequence. Any type of sweeps may be cascaded or linked according to the method, and any amount of padding (listen time) may be inserted between the individual sweep segments.