Helmholtz Centre Potsdam
GFZ German Research Centre for Geosciences
Abstract (EDOC: 11795)
In the framework of the project DESIRE 2006, a part of the reflection traverse was recorded with high-fold vibroseismics. Here (to our knowledge for the first time), strong subharmonic wave-portions were observed, i.e. in addition to the fundamental frequencies prescribed by the utilized vibroseis-sweep (and some less surprising harmonic multiples of them) the actual source signal contains a significant amount with half of the fundamental frequencies after propagating from the baseplate to the geophone. After crosscorrelation with the pilot-sweep these subharmonic partials become especially disastrous (with respect to the seismogram quality) for the simple reason that the corresponding correlation ghosts are imaged towards later traveltimes where the signal amplitudes have already considerably decayed (whereas the ghosts of the less crucial harmonic partials are imaged towards earlier traveltimes where the signal amplitudes are still relatively high). A mathematical procedure has been developed to recognize, separate, and selectively suppress these extremely disturbing (sub)harmonic side-bands. For this, the recorded vibrograms are transformed into a domain, that could be best named as ‘(sub)harmonic domain’, where all (sub)harmonic frequency portions focus separately from each other and can be properly eliminated before backward-transformation. Results of application to DESIRE vibroseis records will be shown.
(2008): Effective suppression of (sub)harmonic noise from vibroseis records. 13th International Symposium on Deep Seismic Profiling of the Contintents and Their Margins - SEISMIX 2008 (Saariselkä, Inari, Finland 2008).