2012 Volume 65 Issue 1_2 Pages 27-36
Recently, a few studies have considered the effect of scattering attenuation to isolate intrinsic attenuation from total attenuation while estimating attenuation in the ultrasonic laboratory measurements. Recent advances in non-destructive methods such as Magnetic Resonance Imaging (MRI) and X-ray computed-tomography (CT) allow heterogeneous microstructures of specimens to be imaged, which enables us to adequately estimate scattering attenuation. However, often, assumptions of attenuation models and methods of estimating attenuation are not fully validated. This article describes the most commonly used attenuation model expressed as an exponential decay, which leads to clarifying the assumptions of the model. Furthermore, I imply that quality factor (Q-value) which is defined as the ratio of the total energy in a system to the energy lost per cycle is a phenomenological quantity. Then, I explain the basis of attenuation estimation by giving an example of the spectral ratio method which is the most common method based on spectral ratios, where data from two receiver distances across a medium of assumed constant Q-value are selected. Dependency of attenuation results on extraction of the first arrival waveform from the observed waveform is also indicated. Finally, I emphasis on the significant influence of scattering effect on attenuation measurements and emphasizes the necessity of revisiting the theory and models of seismic scattering, especially for the case of Mie scattering regime where strong scattering could occur and full waveform modeling is required.
