Viscoacoustic wave propagation in 2-D random media and separation of absorption and scattering attenuation

Geophysics ◽  
1995 ◽  
Vol 60 (2) ◽  
pp. 459-467 ◽  
Author(s):  
Guido Kneib ◽  
Serge A. Shapiro
Keyword(s):  
Wave Propagation ◽  
Random Media ◽  
Wave Amplitude ◽  
Travel Distance ◽  
Scattering Coefficient ◽  
Nonlinear Dependence ◽  
Scattering Attenuation ◽  
Coherent Field ◽  
The Mean ◽  
Seismic Amplitudes

Wave theoretical analysis of scalar, time‐harmonic waves propagating in a constant density medium with isotropic, random velocity fluctuations and being scattered mainly in the forward direction yields a simple and robust procedure that combines the logarithm of the mean wave amplitude with the mean logarithm of the wave amplitude to perform a separation of scattering attenuation and absorption effects. Finite‐difference simulations of wave propagation in 2-D random media with a Voigt‐body rheology illustrate the evolution of wave field fluctuations and demonstrate that the separation procedure works for a wide range of seismic albedos. In the case of no absorption, the logarithms of seismic amplitudes will have a nonlinear dependence on the travel distance if the wavefield fluctuations are small compared to the amplitude of the coherent field. If these fluctuations are large, the logarithms of seismic amplitudes will tend to constant levels independent of the travel distance. In the case of random viscoacoustic media and at propagation distances larger than the inverse of the scattering coefficient of the coherent field, and apart from geometrical spreading, the overall amplitude decrease will be predominated by absorption, even if the absorption coefficient is one order smaller than the scattering coefficient of the coherent field.

On: “Stratigraphic filter theory: Combined effects of parallel bedding and random inhomogeneities” by I. Lerche (GEOPHYSICS, 51, 1531–1537, August 1986).

Geophysics ◽  
1988 ◽  
Vol 53 (7) ◽  
pp. 995-997 ◽  
Author(s):  
Ru‐Shan Wu
Keyword(s):  
Incident Wave ◽  
Random Media ◽  
Seismic Waves ◽  
Mean Field ◽  
Field Approach ◽  
Scattering Attenuation ◽  
Amplitude Attenuation ◽  
Validity Condition ◽  
The Mean ◽  
Field Formalism

In the paper by Lerche (hereafter referred to as Lerche 86), the author compared his formula of effective attenuation (42) based on the mean field attenuation with formula (41), attributed to Wu (1982a), and claimed that Wu’s formula “explicitly assumed that the Born approximation is valid (i.e., that the scattering by the randomly sited centers is from the unperturbed incident wave with no modification to the wave from previous scattering),” while in his result “the modification to the incident wave is taken into account through the statistically sharp mean field” and therefore is “more correct.” However, neither the statement about the validity condition of Wu’s formula not the author’s formula (42) from the mean field approach is correct. In fact, the mean field formalism, when improperly applied to amplitude attenuation, can generate physically meaningless results. The impotence and fallacy of the mean field formalism in dealing with amplitude attenuation in 3-D random media have been recognized since the early 1980s (Wu, 1980, 1982a, b; Sato, 1982a, b). This recognition and the developments thereafter can be considered as one of the major advances in the field of scattering attenuation of seismic waves (Herraiz and Espinosa, 1987; Wu, 1987). Retreat from this advance seems injudicious and illogical. Therefore, I would like to take this opportunity to clarify some basic problems of scattering attenuation.

Wave propagation in random media

1971 ◽  
Vol 45 (4) ◽  
pp. 769-783 ◽  
Author(s):  
M. S. Howe
Keyword(s):  
Wave Propagation ◽  
General Theory ◽  
Random Media ◽  
Random Medium ◽  
Dispersive Media ◽  
Transverse Waves ◽  
Small Deviations ◽  
The Mean ◽  
Density Inhomogeneities ◽  
Rough Boundaries

This paper discusses a general theory of wave propagation through a random medium whose random inhomogeneities are confined to small deviations from the mean. The theory is initially worked out in detail for the propagation of transverse waves along an infinite stretched string whose density is a random function of position. The manner in which the mean wave profile is modified by scattering from the density inhomogeneities is discussed in great detail, with particular emphasis on physical interpretation. The general theory of wave propagation in arbitrary dispersive or non-dispersive media is then discussed, and it is shown how the theory may be extended to wave propagation problems involving scattering from rough boundaries.

Total reflection of a plane wave by a semi-infinite random medium

1972 ◽  
Vol 8 (2) ◽  
pp. 217-229 ◽  
Author(s):  
P. L. Sulem ◽  
U. Frisch
Keyword(s):  
Wave Propagation ◽  
Reflection Coefficient ◽  
Plane Wave ◽  
Random Media ◽  
Numerical Study ◽  
Random Medium ◽  
Exact Result ◽  
Total Reflection ◽  
One Dimensional ◽  
The Mean

An exact result in the theory of wave propagation in random media is presented. Using the ergodic theory of dynamical systems, it is shown that a semi-infinite, one-dimensional random medium is totally reflecting. A direct numerical study shows that the mean reflection coefficient converges exponentially to one.

scholarly journals Anomalous Anderson localization behavior in gain-loss balanced non-Hermitian systems

Nanophotonics ◽  
2020 ◽  
Vol 10 (1) ◽  
pp. 443-452
Author(s):  
Tianshu Jiang ◽  
Anan Fang ◽  
Zhao-Qing Zhang ◽  
Che Ting Chan
Keyword(s):  
Wave Propagation ◽  
Electromagnetic Waves ◽  
Anderson Localization ◽  
Random Media ◽  
Normal Incidence ◽  
Disordered Media ◽  
One Dimensional ◽  
Gain Loss ◽  
The Waves ◽  
Localization Behavior

AbstractIt has been shown recently that the backscattering of wave propagation in one-dimensional disordered media can be entirely suppressed for normal incidence by adding sample-specific gain and loss components to the medium. Here, we study the Anderson localization behaviors of electromagnetic waves in such gain-loss balanced random non-Hermitian systems when the waves are obliquely incident on the random media. We also study the case of normal incidence when the sample-specific gain-loss profile is slightly altered so that the Anderson localization occurs. Our results show that the Anderson localization in the non-Hermitian system behaves differently from random Hermitian systems in which the backscattering is suppressed.

scholarly journals Management of Chipping Operations in Polish Forests

2020 ◽  
Vol 3 (1) ◽  
pp. 56
Author(s):  
Arkadiusz Gendek ◽  
Monika Aniszewska ◽  
Witold Zychowicz ◽  
Tadeusz Moskalik ◽  
Jan Malaťák ◽  
...  
Keyword(s):  
Fuel Consumption ◽  
Travel Distance ◽  
Operating Efficiency ◽  
Site Location ◽  
Work Shift ◽  
Work Site ◽  
The Mean ◽  
The Impact ◽  
Machine Base

The aim of the research was to verify the impact of selected parameters on the efficiency and organization of chipper operations. The paper analyzes chipping operations in Polish forests with a focus on work site location, overnight chipper location, chipper workload per site, fuel consumption, and work shift duration, as all of these factors may affect operating efficiency. The mean chipper travel distance between sites during a shift ranged from 4.74 km to 9.5 km (chippers moved on average every other day). The mean work shift duration was 12.4 h. At the end of a shift, the chippers traveled on average from 4.2 km to 6.3 km to an overnight location. At the beginning of a workday, the chippers were dispatched to sites at a distance of 2.5 km to 4.0 km. The average fuel consumption of the forwarder-mounted chippers was 16 L/h and that of the truck-mounted chipper was 7.7 L/h. It was found that the following actions have a decisive influence on the effectiveness of the operation of the chippers: determination of the size of individual tasks and the deployment of successive forest areas, indication of the proper location of the machine base, and the method of accessing the forest area.

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