Luminescence and ESR dating Beta-dose attenuation for various grain shapes calculated by a Monte-Carlo method
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A simple artificial neural network is considered for real-time estimation of excess atmospheric attenuation on a satellite communication link with known attenuation at two frequencies. All atmospheric contributors to attenuation are considered except for gases. The network has a two-layer feed-forward structure with 32 neurons in the hidden layer. Its performance is evaluated by computer simulation using 447 hours of measured attenuation data at 20, 40, and 50 GHz. Estimated attenuation tracks well the measured attenuation at 50 GHz. Estimation error standard deviation is 0.36 dB. RMS error is a function of attenuation: it increases slowly with attenuation, but the ratio of error to attenuation decreases with increasing attenuation. This approach accurately estimates excess attenuation without requiring assumptions, but required training data. (4 pages)
Correction for attenuation
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We analyze a range of VSP datasets for evidence of fracture related attenuation anisotropy, focusing on three attributes: P-wave attenuation anisotropy, differential shear-wave attenuation and frequency dependent shear-wave splitting. We find examples of all three phenomena and are able to reproduce the behaviour with well constrained, unified, theoretical models. Our results suggest a correlation between attenuation anisotropy and fracture properties. It is apparent that in all cases the reservoir displays much higher attenuation than the overburden. Measuring relative attenuation appears to be more robust than measuring absolute attenuation.
Overburden
Shear waves
Anelastic attenuation factor
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E-19 NUMERICAL STUDY OF SCATTERING ATTENUATION IN FRACTURED MEDIA – FREQUENCY DEPENDENCE AND EFFECTS OF CHARACTERISTIC LENGTH SCALES Introduction 1 Seismic attenuation is in general a combined effect of absorption (intrinsic attenuation) which is affected by lithological parameters and scattering (apparent) attenuation which is related to structural parameters. Which of these two mechanisms dominates in any given situation depends on the relative wavelengths of the seismic wave and the heterogeneities of the fracture system. In this study we deal exclusively with scattering attenuation. Synthetic modeling studies with and without intrinsic attenuation show that the contribution of scattering attenuation is significant.
Anelastic attenuation factor
Attenuation length
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