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Soner Bekleric Title of Thesis: Nonlinear Prediction via Volterra Ser

Soner Bekleric Title of Thesis: Nonlinear Prediction via Volterra Ser

Soner Bekleric Title of Thesis: Nonlinear Prediction via Volterra Ser

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series in this thesis has been truncated to a third-order <strong>Volterra</strong> series. <strong>Prediction</strong><br />

coefficients are found <strong>via</strong> least squares solutions. The real and synthetic data ex-<br />

amples showed that <strong>Volterra</strong> series modeling modeling is more versatile than linear<br />

prediction at the time <strong>of</strong> representing signals such as those arising in the context <strong>of</strong><br />

exploration seismology.<br />

Events that exhibit strong curvature cannot be modeled <strong>via</strong> linear f − x predic-<br />

tion filters. I can model these events by implementing the <strong>Volterra</strong> algorithm. The<br />

optimum filter length <strong>of</strong> a linear model <strong>of</strong> order (p) or a nonlinear <strong>Volterra</strong> model<br />

<strong>of</strong> order (p, q, r) can be computed <strong>via</strong> inspection <strong>of</strong> the residuals. A more practical<br />

method is desirable but at this stage looking for evidence <strong>of</strong> under-over fitting using<br />

sophisticated statistical analysis method was beyond the scope <strong>of</strong> this study.<br />

Different synthetic and real data examples showed that the modeling <strong>of</strong> events<br />

with linear moveout can be predicted mainly <strong>via</strong> linear prediction coefficients and<br />

cubic prediction coefficients. The contribution <strong>of</strong> quadratic parts to events with<br />

linear moveouts is negligible. In addition to this, events that exhibit curvature<br />

can be modeled properly with nonlinear terms <strong>of</strong> a <strong>Volterra</strong> series. Finally, it is<br />

important to stress that waveforms that exhibit linear moveout can be predicted<br />

with a linear system. Conversely, when waveforms exhibit nonlinear moveout, which<br />

translates in the f − x domain as non stationary signals, the nonlinear part <strong>of</strong> the<br />

<strong>Volterra</strong> system helps in predicting the signal.<br />

Another application <strong>of</strong> the nonlinear <strong>Volterra</strong> model in this thesis is adaptive<br />

subtraction <strong>of</strong> multiples. Elimination <strong>of</strong> multiples is a common problem in explo-<br />

ration seismology. In this case the prediction coefficients have been designed as<br />

prediction error filters (PEF). I used this algorithm to annihilate multiples from<br />

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