Browsing by Author "Izadi, Hormoz"

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    Application of 1-D Inverse Scattering to Inversion of Laboratory Seismic Data and Distributed Acoustic Sensing Data
    (2020-09-02) Izadi, Hormoz; Innanen, Kristopher A.; Karchewski, Brandon; Hobill, David W.; Trad, Daniel O.
    The Born series provides a framework for constructing a connection between Earth model parameters and a wavefield characterised by perturbation about a known reference wavefield. The inverse scattering series provides a linear and a nonlinear expression for approximating Earth’s model parameters. Based on our results, the linear expression provides an accurate approximation of the 1-D depth varying velocity profile. However, with increasing contrast, one has to utilise the nonlinear expression for increased accuracy. In seismic inversion, a major problem relates to the bandlimited nature of recorded seismic data, limiting the inversion for absolute amplitudes. Numerical results on a 1-D synthetic model demonstrate the capacity of the algorithm to recover low frequency information, critical for accurate inversion. By extending the application of projection onto convex sets (POCS) to 1-D physical modelling data, we obtain an accurate reconstruction of the dataset. Inversion of the data demonstrates the advantage of nonlinear inverse scattering in approximating a relatively accurate velocity profile. In comparison, the linear scattering expression fails to provide a reasonable estimate of reflectors beyond the first interface. One of the areas of growing interest in the field of exploration geophysics is the application of optical fibre sensing technology. Recent studies suggest the advantage of this technique in providing a greater range of applicability in comparison to traditional methods. Among various Optical time-domain reflectometer (OTDR) arrangements, the intensity based measurement is generally limited by the nonlinear response of a signal to external disturbances such as strain. This has served as a motivation in the second half of this thesis to frame the problem as a 1-D scattering problem, in an attempt to apply the Born series to recover information related to variations in external measurements such as strain. Our attempts to utilise the Born series fails to provide an accurate estimation of changes in location of scattering points. This is primarily due to the complexity of the model and interference of backscattered optical pulse within the fibre. Continued research could potentially provide a framework for a robust detection of external perturbation based on variation in intensity.
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    Local signal regularity and smoothness as a means for seismic Q estimation
    (2012-12-20) Izadi, Hormoz; Innanen, Kris; Lamoureux, Michael
    In seismic signal analysis, irregular structures and points of sharp variation contain critical information, thus making the study of a signal's local properties an appropriate mechanism for obtaining information from seismic data. The local regularity of a seismic event is determined by the wavelet transform modulus maxima and the associated Lipschitz exponent. As a means of classifying regularities of a signal and estimating the associated Lipschitz exponent, the linear and non-linear Mallat-Hwang-Zhong (MHZ) signal model based on the wavelet theory is reviewed and developed. For isolated seismic events, resembling a delta function or a Heaviside function, the linear MHZ model is used to estimate the associated Lipschitz exponent and subsequently verify the theoretical properties of the exponent. However for practical settings, in particular, band-limited signal events, the more complex non-linear MHZ signal model must be applied in order to estimate the local regularity and the additional smoothness parameter. Based on the synthetic vertical seismic profile (VSP) modelling, a relatively complicated mathematical mapping between the Lipschitz exponent and seismic quality factor Q is obtained. However, analysing the smoothness parameter results in an invertible power law relation between the aforementioned parameter and Q. Applying the non-linear MHZ model to the Ross Lake VSP field data captures the general absorption trend estimated by Zhang and Stewart (2006). Furthermore, the power law relation provides geophysically reasonable Q values comparable to the estimated values using traditional methods, such as the steepest descent. However, for a more robust mathematical relation between the Lipschitz exponent, smoothness parameter and seismic quality factor Q, additional theoretical and field data analysis is required.