Harmonic decomposition of a Vibroseis sweep using Gabor analysis

Christopher B. Harrison, Gary F. Margrave, Michael P. Lamoureux, Arthur Siewert, Andrew Barrett

In traditional Vibroseis surveys the harmonic frequencies generated by the vibrator are seen as undesirable noise distortions. These distortions are attributed to various factors such as nonlinear coupling of the vibrator to the ground, nonlinear effects in the vibrator and inadequacy of the feedback system. These harmonic effects cause a correlation-ghost forerunner or a tail at both positive and negative correlation times if the harmonically distorted sweep is used as the correlation operator. Over the years techniques for bulk attenuation of these harmonic effects have been developed to enhance Vibroseis seismic imaging. An innovative approach, however, is proposed to decompose Vibroseis sweeps into their respective fundamental and harmonic components such that the harmonics and their higher frequencies can be used for seismic imaging or more accurate filter design. The decomposition is accomplished through the use of the Gabor transform to produce broad band estimates of the fundamental and harmonics of the Vibroseis sweep. The method is tested on both a synthetic sweep with time varying amplitude and phase, as well as field data.