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Physical Fundamentals
Published in Iain H. Woodhouse, Introduction to Microwave Remote Sensing, 2006
We will see later that a key component of imaging radar systems is that they are able to maintain coherency between consecutive pulses, and because of this it is possible to assume the waves are always coherent. In passive systems, it is not so obvious that the source may have any degree of coherency, but under particular conditions (i.e. short time intervals and over small spatial scales) passive sources will also maintain a degree of coherence.
Philosophy, policies, procedures and practices: The four ‘P’s of flight deck operations
Published in Neil Johnston, Nick McDonald, Ray Fuller, Aviation Psychology in Practice, 2017
A complex human–machine system is more than merely one or more operators and a collection of hardware components. To operate a complex system successfully, the human–machine system must be supported by an organizational infrastructure of operating concepts, rules, guidelines and documents. The coherency, in terms of consistency and logic, of such operating concepts is vitally important for the efficiency and safety aspect of any complex system.
Spatial variability of the seismic ground motion at the dam-foundation interface of an arch dam
Published in Jean-Jacques Fry, Norihisa Matsumoto, Validation of Dynamic Analyses of Dams and Their Equipment, 2018
E. Koufoudi, E. Chaljub, F. Dufour, N. Humbert, E. Robbe, E. Bourdarot
Coherency estimation is a stochastic approach widely used to estimate the spatial variation of the motions during the prominent strong-motion shear (S-) wave window. By definition, coherency characterizes the variation in Fourier phase and expresses the loss of correlation between two time series. The lagged coherency, of the seismic motion between the stations j and k is given by the modulus of the ratio of the smoothed cross-spectrum of the two time series to the geometric mean of the respective, identically smoothed, auto power spectra (Equation 1). The value of lagged coherency is zero for uncorrelated processes and it is equal to one for linearly correlated processes. () (γ¯jk(ω))=(S¯jk(ω))(S¯¯jj(ω)S¯kk(ω))
Behavior of a RC Frame Under Differential Seismic Excitation
Published in Journal of Earthquake Engineering, 2020
Maria Ghannoum, Afifa Imtiaz, Stephane Grange, Matthieu Causse, Cécile Cornou, Julien Baroth
Here we follow the stochastic procedure for the estimation of spatial variability in terms of coherency from the synthetics, as described in Imtiaz [2015]. This allows the estimation of deterministic (or coherent) and stochastic (or incoherent) part of the ground motion. The most commonly quoted measure of coherency is the lagged coherency. It indicates the degree of linear correlation (i.e. similarity) between the random processes recorded at the two stations under consideration. The two time histories are aligned using the time lag that leads to the largest correlation of the two ground motions. Thus this coherency measure is assumed to remove the effects of systematic delay due to the simple inclined plane wave propagation, often called as the wave-passage effect. Let us consider two ground motions, and , recorded at locations j and k, respectively. A taper window, , is applied to that envelopes the strong shaking. The tapered time series is, then, given by . The Fourier transform, , of the tapered time series is:
Depth Coherency Analysis for Strong Seismic Motions from KiK-Net
Published in Journal of Earthquake Engineering, 2021
Lagged coherency is the most commonly cited coherency measure; hence, only lagged coherency will be analyzed and presented in this paper. This section reviews the methodologies of coherencies of seismic motions and introduces the models that can be used in engineering practices presented in the literature. The reason to present spatial coherency instead of depth coherency is that there is very little literature on depth coherency at the time of writing.