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How to adapt numerical simulation of wave propagation and ultrasonic laboratory experiments to be comparable? A case study for a complex topographic model Running head: Comparison of synthetic and lab data

A B S T R A C TSeismic wavefield scattering from a statistically randomly rough interface in a multilayered piecewise homogeneous medium is studied in 3D. The influence of the surface roughness on the scattered wavefield is analysed numerically by using a finite-difference operator in the acoustic domain. Since interface scattering in the real practical sense is a 3D physical phenomenon, we show in this work that the scattering response of a randomly rough interface is not the same in 3D situations as in the 2D cases described in some earlier works. For a given interface roughness height in 3D, an interface roughness height at least three times greater is required to produce an equivalent phase scattering effect in 2D situations, for a given correlation length of the interface roughness scale. Based on observations from spectral analysis, we show that scattering results principally in de-phasing and frequency band-limiting of the incident wavefront, the frequency band-limiting properties being comparable to cases reported in the literature for absorption and thin-layer filtering. The interface scattering phenomenon should be critically considered when using amplitude and phase information from seismic signal during inversion processes. I N T R O D U C T I O NThe amplitude and phase of seismic signal are two important parameters which are normally exploited during inversion processes in reflection seismology. In order to be able to use information from these parameters for inversion purposes, it is essential that the method for modelling the subsurface includes all the physical phenomena that affect these parameters. Interface scattering is one such important physical phenomenon almost overlooked in reflection seismology, despite its considerable impact on these parameters. It is well known that a scattering regime depends on the relationship between the wavelength and the scale of heterogeneity. In this work, we show that the effect of interface scattering becomes significant when the interface roughness height attains 1/5 of the wavelength of the incident wave (λ/5). This might result in errors which could at times be as much as 50% in the quantitative interpretation of the amplitude of reflected waves. Thus, all inversion methods using these parameters to recover the acoustic impedances or stratigraphy of the subsurface should take this important phenomenon into consideration.Interface scattering of a seismic wavefield is associated with the spatial distributions of irregular geological contacts at the interface between layers of the stratified earth. It is well known that surface roughness is not an intrinsic property of a surface but depends on the properties of the wave that is being scattered (Ogilvy 1991). The scale of the interface roughness in relation to the wavelength of the incident wave is thus crucial in determining how energy is scattered from an interface. In optical and radar remote sensing, surfaces with roughness of the order of λ/10, where λ is the wavelength of the incident C 2005 European