Suppression of guided waves using the Karhunen-Loève transform
Résumé
Guided waves are the major source of coherent noise, either on terrestrial or on marine seismic data, because the signals they produce are much stronger in amplitude than the reflected ones. In marine contexts, these waves exhibit characteristics that depend on the water depth, on the geometry and on the material properties of the substrata. Guided waves - or ground roll - are dispersive, which constitutes their main property. This means that each frequency component of the wave travels at a different velocity, in the sense that smaller and larger wavelengths are respectively influenced by the seismic properties of the shallower and deeper parts of the media. Due to their linear moveout-versus-offset characteristics, it may be possible to suppress the guided waves by dip filtering techniques. Unfortunately, this kind of filtering causes serious distortion of the signal when the amplitude of guided waves is much stronger than that of reflection (Liu 1999). The method developed here consists of extracting the guided waves from common-shot gathers without disturbing the reflection signals.