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Nouvelles méthodes de séparation des champs d'ondes en sismique

Abstract : The aim of this work is to bring a contribution to the wave field separation, in seismics, using two advanced techniques. The first technique, based on the pattern recognition, uses the signal shape associated to the seeked echo to extract it. We show, through applications on Vertical Seismic Profiles (VSP) data, that this technique seems like a more effective filter than the low-pass frequency filter, especially when noise is not localized in a given frequency band, and do not require nor a priori information on the received signal frequency band neither on its phase. In addition, we confirm that the pattern recognition is a good tool for P and SV polarized waves filtering, on three components data for offset VSP. We show, in this study, that the use of the Poline directional filter as pre-processing on the initial data allows an identification and an automatic extraction of the P and SV training signals; the efficiency of the method is thus improved and its use made easier. The second technique, very adapted for the non-stationary signals, is based on the wavelet transform and its rebuilding formula, to detect and extract locally, in the time-scale field, a quite particular echo on the seismic recording. Filtering quality depends on the delimitation of the echo to be filtered in the time-scale space and the adopted filtering process. We show, on a vibroseis seismic reflection recording, the efficiency of this method to filter the ground roll made up, in our case, of two slow and fast pseudo-Rayleigh waves, with a strong energy. We present the results for two different filtering processes, one based on the restoring of the transform coefficients in the selected zone and the other on their attenuation (roll-off). We propose, finally, the use of this technique to extract and characterize the two pseudo-Rayleigh waves, very useful waves for geotechnic studies.
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Zahia Benaïssa Hameg. Nouvelles méthodes de séparation des champs d'ondes en sismique. Géophysique [physics.geo-ph]. Université des Sciences et de la Technologie Houari Boumediène-Alger, 2007. Français. ⟨tel-01765384⟩

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