Wave Propagation, Scattering and Imaging Using Dual-domain One-way and One-return Propagators

— Dual-domain one-way propagators implement wave propagation in heterogeneous media in mixed domains (space-wavenumber domains). One-way propagators neglect wave reverberations between heterogeneities but correctly handle the forward multiple-scattering including focusing/defocusing, diffraction, refraction and interference of waves. The algorithm shuttles between space-domain and wavenumber-domain using FFT, and the operations in the two domains are self-adaptive to the complexity of the media. The method makes the best use of the operations in each domain, resulting in efficient and accurate propagators. Due to recent progress, new versions of dual-domain methods overcame some limitations of the classical dual-domain methods (phase-screen or split-step Fourier methods) and can propagate large-angle waves quite accurately in media with strong velocity contrasts. These methods can deliver superior image quality (high resolution/high fidelity) for complex subsurface structures. One-way and one-return (De Wolf approximation) propagators can be also applied to wave-field modeling and simulations for some geophysical problems. In the article, a historical review and theoretical analysis of the Born, Rytov, and De Wolf approximations are given. A review on classical phase-screen or split-step Fourier methods is also given, followed by a summary and analysis of the new dual-domain propagators. The applications of the new propagators to seismic imaging and modeling are reviewed with several examples. For seismic imaging, the advantages and limitations of the traditional Kirchhoff migration and time-space domain finite-difference migration, when applied to 3-D complicated structures, are first analyzed. Then the special features, and applications of the new dual-domain methods are presented. Three versions of GSP (generalized screen propagators), the hybrid pseudo-screen, the wide-angle Padé-screen, and the higher-order generalized screen propagators are discussed. Recent progress also makes it possible to use the dual-domain propagators for modeling elastic reflections for complex structures and long-range propagations of crustal guided waves. Examples of 2-D and 3-D imaging and modeling using GSP methods are given.     

On the sensitivity of mesoscale models to surface-layer parameterization constants

The Colorado State University standard mesoscale model is used to evaluate the sensitivity of one-dimensional (1D) and two-dimensional (2D) fields to differences in surface-layer parameterization constants. Such differences reflect the range in the published values of the von Karman constant, Monin-Obukhov stability functions and the temperature roughness length at the surface. The sensitivity of 1D boundary-layer structure, and 2D sea-breeze intensity, is generally less than that found in published comparisons related to turbulence closure schemes generally.     

Expert judgment and climate forecasting: A methodological critique of “climate change to the year 2000”

The National Defense University's study of climate change to the year 2000 was based largely on the judgments of the members of two expert panels. Although the study has been widely distributed and apparently read by policy makers in the U.S. and abroad, the method of eliciting and analyzing expert judgment has not been critically reviewed. This paper uses the literature on judgment and subjective probability to evaluate the expert judgment methods used in the study.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Contribution à la surveillance de l'activité de l'Etna à partir de l'étude des zones fumerolliennes

Resume La convection de la vapeur d'eau formée en profondeur dans une zone fumerollienne crée en surface une anomalie hydrique, thermique et électrique, cette dernière pouvant être la plus sensible à une variation de l'activité thermique profonde. L'amplitude des anomalies dépend de la position du site par rapport à la configuration de l'activité magmatique, mais aussi des conditions hydrogéologiques locales. La surveillance spatiale et temporelle des éruptions à partir du phénomène convectif hydrique doit tenir compte de ces conditions.

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The water steam convection existing below a fumarolic area creates hydraulic, thermal and electric anomalies, the electric anomaly being probably the most correlated to a change of the deep thermal activity. The anomaly range depends on the position of the site connected with the configuration of the magmatic activity, but also on the local hydrogeologic conditions. The spatial and temporal surveillance of the eruptions based on these convective data should take into consideration these conditions.