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| Ker, Stephan; Le Gonidec, Yves. |
| Multiscale seismic attributes based on the wavelet transform properties have been recently introduced and successfully applied to identify the geometry of a complex seismic reflector in an elastic medium. In the present paper, we extend this quantitative approach to anelastic media where intrinsic attenuation modifies the seismic attributes and thus requires a specific processing to retrieve them properly. The method assumes both an attenuation linearly dependent with the seismic wave frequency and a seismic source wavelet approximated with a Gaussian derivative function. We highlight a quasi-conservation of the Gaussian character of the wavelet during its propagation. We show that this shape can be accurately modeled by a Gaussian derivative function... |
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| Ano: 2018 |
URL: http://archimer.ifremer.fr/doc/00409/52034/52700.pdf |
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| Ker, Stephan; Le Gonidec, Yves; Gibert, Dominique. |
| A wavelet-based method was presented in a previous work to introduce multiscale seismic attributes for high-resolution seismic data. Because of the limited frequency bandwidth of the seismic source, we observed distortions in the seismic attributes based on the wavelet response of the subsurface discontinuities (Le Gonidec et al.). In this paper, we go further in the seismic source-correction by considering L´evy alpha-stable distributions introduced in the formalism of the continuous wavelet transform (CWT). The wavelets are Gaussian derivative functions (GDF), characterized by a derivative order. We show that a high-resolution seismic source, after a classical signature processing, can be taken into account with a GDF. We demonstrate that in the... |
| Tipo: Text |
Palavras-chave: Wavelet transform; Wave propagation; Acoustic properties. |
| Ano: 2012 |
URL: http://archimer.ifremer.fr/doc/00090/20155/17828.pdf |
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| Ker, Stephan; Le Gonidec, Yves; Marie, Louis; Thomas, Yannick; Gibert, Dominique. |
| Seismic Oceanography is coming of age as an established technique of observation of the thermohaline structure of the ocean. The present paper deals with the seismic reflectivity of the Armorican Shelf seasonal thermocline, west of France, based on two seismic experiments performed with a sparker source. The peak frequency was 500 Hz for the ASPEX experiment, where the thermocline was located at 27 m water depth, and reduced to 400 Hz associated to a higher source level for the IFOSISMO experiment, where the thermocline was 12 m deeper. Despite this settings, only the first experiment could clearly highlight the thermocline reflector, providing the first seismic observation of a shallow oceanic structure. To better understand the limitation of... |
| Tipo: Text |
Palavras-chave: Thermocline; Seismic method; Wavelet analysis; Acoustic. |
| Ano: 2015 |
URL: https://archimer.ifremer.fr/doc/00254/36535/35066.pdf |
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| Ker, Stephan; Le Gonidec, Yves; Gibert, D.; Marsset, Bruno. |
| We propose a wavelet-based method to characterize acoustic impedance discontinuities from a multiscale analysis of seismic reflected waves. Our approach relies on the analysis of ridge functions which contain most of the information of the wavelet transform in a sparse support. This method falls in the framework of the wavelet response (WR) introduced by Le Gonidec et al. which analyses the impedance multiscale behaviour by propagating dilated wavelets into the medium. We further extend the WR by considering its application to broad-band seismic data. We take into account the bandpass filter effect related to the limited frequency range of the seismic source. We apply the method to a deep-water seismic experiment performed in 2008 during the ERIG3D cruise... |
| Tipo: Text |
Palavras-chave: Wavelet transform; Seismic attenuation; Wave propagation; Acoustic properties. |
| Ano: 2011 |
URL: http://archimer.ifremer.fr/doc/00049/15994/13449.pdf |
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| Ker, Stephan; Le Gonidec, Yves. |
| A varying Q factor with depth induces modifications of seismic wave features due to anelastic propagation but also reflections at the discontinuities. Standard signal analysis methods often neglect the reflection contribution when assessing Q values from seismic data. We have developed an analytical quantification of the cumulative effects of both the propagation and reflection contributions by considering the Kjartansson's model and a seismic plane wave at normal incidence on a step-like discontinuity. We show that the cumulative effects are equivalent to a frequency filter characterized by a bandform and phase that both depend on the ratio between the elastic and anelastic contrasts. When considering this filter applied to a Ricker wavelet, we establish... |
| Tipo: Text |
Palavras-chave: Seismic attenuation; Q factor; Anelasticity; Seismic data analysis. |
| Ano: 2020 |
URL: https://archimer.ifremer.fr/doc/00640/75240/75398.pdf |
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