Small-scale spatial fluctuations of a v.l.f. wave field in the ionosphere in the zone close to the transmitter

1967 ◽  
Vol 3 (7) ◽  
pp. 298
Author(s):  
M.P. Aubry
Keyword(s):  
Wave Field ◽  
Small Scale ◽  
Spatial Fluctuations

scholarly journals Small-scale diagenetic facies heterogeneity controls porosity and permeability pattern in reservoir sandstones

2020 ◽  
Vol 79 (18) ◽  
Author(s):  
Matthias Heidsiek ◽  
Christoph Butscher ◽  
Philipp Blum ◽  
Cornelius Fischer
Keyword(s):  
Reservoir Rock ◽  
Rock Properties ◽  
Small Scale ◽  
Reservoir Quality ◽  
Permian Basin ◽  
Gas Reservoirs ◽  
Spatial Fluctuations ◽  
Porosity And Permeability ◽  
Reservoir Sandstones ◽  
Diagenetic Facies

Abstract The fluvial-aeolian Upper Rotliegend sandstones from the Bebertal outcrop (Flechtingen High, Germany) are the famous reservoir analog for the deeply buried Upper Rotliegend gas reservoirs of the Southern Permian Basin. While most diagenetic and reservoir quality investigations are conducted on a meter scale, there is an emerging consensus that significant reservoir heterogeneity is inherited from diagenetic complexity at smaller scales. In this study, we utilize information about diagenetic products and processes at the pore- and plug-scale and analyze their impact on the heterogeneity of porosity, permeability, and cement patterns. Eodiagenetic poikilitic calcite cements, illite/iron oxide grain coatings, and the amount of infiltrated clay are responsible for mm- to cm-scale reservoir heterogeneities in the Parchim formation of the Upper Rotliegend sandstones. Using the Petrel E&P software platform, spatial fluctuations and spatial variations of permeability, porosity, and calcite cements are modeled and compared, offering opportunities for predicting small-scale reservoir rock properties based on diagenetic constraints.

scholarly journals Internal Waves and Mixing near the Kerguelen Plateau

2015 ◽  
Vol 46 (2) ◽  
pp. 417-437 ◽  
Author(s):  
Amelie Meyer ◽  
Kurt L. Polzin ◽  
Bernadette M. Sloyan ◽  
Helen E. Phillips
Keyword(s):  
Internal Wave ◽  
Wave Field ◽  
Internal Waves ◽  
Large Scale ◽  
Polar Front ◽  
Frontal Region ◽  
Small Scale ◽  
Kerguelen Plateau ◽  
Flow Strength ◽  
Internal Wave Field

AbstractIn the stratified ocean, turbulent mixing is primarily attributed to the breaking of internal waves. As such, internal waves provide a link between large-scale forcing and small-scale mixing. The internal wave field north of the Kerguelen Plateau is characterized using 914 high-resolution hydrographic profiles from novel Electromagnetic Autonomous Profiling Explorer (EM-APEX) floats. Altogether, 46 coherent features are identified in the EM-APEX velocity profiles and interpreted in terms of internal wave kinematics. The large number of internal waves analyzed provides a quantitative framework for characterizing spatial variations in the internal wave field and for resolving generation versus propagation dynamics. Internal waves observed near the Kerguelen Plateau have a mean vertical wavelength of 200 m, a mean horizontal wavelength of 15 km, a mean period of 16 h, and a mean horizontal group velocity of 3 cm s−1. The internal wave characteristics are dependent on regional dynamics, suggesting that different generation mechanisms of internal waves dominate in different dynamical zones. The wave fields in the Subantarctic/Subtropical Front and the Polar Front Zone are influenced by the local small-scale topography and flow strength. The eddy-wave field is influenced by the large-scale flow structure, while the internal wave field in the Subantarctic Zone is controlled by atmospheric forcing. More importantly, the local generation of internal waves not only drives large-scale dissipation in the frontal region but also downstream from the plateau. Some internal waves in the frontal region are advected away from the plateau, contributing to mixing and stratification budgets elsewhere.

scholarly journals Spectrally Resolved Energy Dissipation Rate and Momentum Flux of Breaking Waves

2008 ◽  
Vol 38 (6) ◽  
pp. 1296-1312 ◽  
Author(s):  
Johannes R. Gemmrich ◽  
Michael L. Banner ◽  
Chris Garrett
Keyword(s):  
Energy Dissipation ◽  
Wave Field ◽  
Wave Energy ◽  
Dissipation Rate ◽  
Momentum Flux ◽  
Phase Speed ◽  
Breaking Waves ◽  
Energy Dissipation Rate ◽  
Small Scale ◽  
Breaking Wave

Abstract Video observations of the ocean surface taken from aboard the Research Platform FLIP reveal the distribution of the along-crest length and propagation velocity of breaking wave crests that generate visible whitecaps. The key quantity assessed is Λ(c)dc, the average length of breaking crests per unit area propagating with speeds in the range (c, c + dc). Independent of the wave field development, Λ(c) is found to peak at intermediate wave scales and to drop off sharply at larger and smaller scales. In developing seas breakers occur at a wide range of scales corresponding to phase speeds from about 0.1 cp to cp, where cp is the phase speed of the waves at the spectral peak. However, in developed seas, breaking is hardly observed at scales corresponding to phase speeds greater than 0.5 cp. The phase speed of the most frequent breakers shifts from 0.4 cp to 0.2 cp as the wave field develops. The occurrence of breakers at a particular scale as well as the rate of surface turnover are well correlated with the wave saturation. The fourth and fifth moments of Λ(c) are used to estimate breaking-wave-supported momentum fluxes, energy dissipation rate, and the fraction of momentum flux supported by air-entraining breaking waves. No indication of a Kolmogorov-type wave energy cascade was found; that is, there is no evidence that the wave energy dissipation is dominated by small-scale waves. The proportionality factor b linking breaking crest distributions to the energy dissipation rate is found to be (7 ± 3) × 10−5, much smaller than previous estimates.

Full Waveform Inversions of Borehole Transient Electromagnetic Virtual Wave Fields and Potential Applications

2020 ◽  
Vol 25 (2) ◽  
pp. 211-222
Author(s):  
Fan Tao ◽  
Qi Zhipeng ◽  
Yan Bin ◽  
Zhao Zhao ◽  
Wang Bingchun ◽  
...  
Keyword(s):  
Wave Field ◽  
Shanxi Province ◽  
Small Scale ◽  
Detection Accuracy ◽  
Dynamic Correction ◽  
Wave Fields ◽  
Full Waveform ◽  
Transient Electromagnetic ◽  
Good Imaging ◽  
Imaging Results

The transient electromagnetic method (TEM) for boreholes uses fixed source loops to launch at excavation faces, and is able to realize the mobile reception of secondary fields in the boreholes and detections of low-resistance hazards. This method is known as high detection accuracy, due to the fact that the receiving points are close to the anomalies. However, the interpretation method for this device has not yet been perfected. The present study's goal was to realize the interpretations of boreholes TEM based on inverse transform algorithms of the TEM wave-fields and full waveform inversions. It was found that under the conditions of transient electromagnetic virtual wave-fields, the characteristics of the virtual wave-field time-distance curves of the two-dimensional device could be examined, and a corresponding dynamic correction algorithm was successfully obtained. The wave-field velocities were analyzed using an equivalent conductive plane method. Additionally, the pseudo-seismic inversions of the tunnel-borehole TEM data were realized using full waveform inversion technology. Then, the inversion results of the three-dimensional numerical simulations, flume physical simulations, and downhole field simulations were calculated. It was observed that good imaging results had been obtained for small-scale borehole radial anomalies. Finally, the proposed method was applied to the engineering practices in an underground coal mine in Shanxi Province. The practicability and effectiveness of the proposed method in the fine detection of the properties, forms, and scale of water-logged goaf roadways were successfully tested in the field. The research results indicated that the roadway-borehole transient electromagnetic detection method was complementary to the underground geophysical exploration and drilling, and could be effectively applied in the detection of water-logged goaf roadways.

scholarly journals The Extragalactic Diffuse Background in the Far Ultraviolet

1990 ◽  
Vol 139 ◽  
pp. 307-316
Author(s):  
Francesco Paresce
Keyword(s):  
Line Of Sight ◽  
Small Scale ◽  
Zodiacal Light ◽  
Dust Layer ◽  
High Ionization ◽  
Spatial Fluctuations ◽  
Diffuse Background ◽  
Far Ultraviolet ◽  
Near Future ◽  
Uv Range

Due mainly to the minimal contaminating effects of zodiacal light and direct stellar emission, the far UV wavelength band from 912 to à 2000 å is ideally suited, in principle at least, for an accurate measurement of a diffuse background component due to sources outside our own galaxy. The cosmological significance of such radiation is of great current interest as it certainly includes the cumulative line-of-sight effect of galaxies and quasars and may include emission from both a lukewarm intergalactic medium and decaying massive particles such as neutrinos, photinos, etc. The radiation required to maintain the IGM at its known high ionization level should also, in any case, appear clearly in this band due to redshift and lookback time effects, thereby providing a crucial clue as to its presently obscure origins. Just how accurately this component can be measured in practice, however, clearly depends on how well we understand the probably dominant galactic component from which it must be disentangled in one way or another except, possibly, at the galactic poles. The residual emission there in this band is on the order of a few ×102 photons cm−2 s−1 sr−1 å−1, of which perhaps as many as 50 units are almost certainly due to galaxies since the small-scale spatial fluctuations corresponding to this flux almost exactly mimic those expected from the known spatial distribution of galaxies. The rest must come from a presently uncertain source, most likely a residual tenuous dust layer at the galactic poles. This latter possibility is at least consistent with recent IRAS results on the diffuse IR background at 100 μm and very sensitive HI, 21 cm measurements in these regions, but an extragalactic origin cannot be presently ruled out. Higher spatial and spectral resolution observations throughout the entire far UV range planned for the near future from orbiting platforms are expected to resolve this last but critically important issue.

scholarly journals Occurrence of “precursors” of PKP-waves in the layered radial-symmetric Earth

2019 ◽  
Vol 489 (1) ◽  
pp. 84-88
Author(s):  
A. G. Fatyanov ◽  
V. Yu. Burmin
Keyword(s):  
Analytical Solution ◽  
Wave Field ◽  
Travel Time ◽  
High Frequency ◽  
Spherical Model ◽  
Outer Core ◽  
Small Scale ◽  
Longitudinal Waves ◽  
High Frequency Oscillations ◽  
The Earth

It is generally accepted that PKP‑waves precursors, which are observed on a real data ahead of PKP‑waves, are explained by scattering on small-scale inhomogeneities in the lower mantle. In this paper, a stable analytical solution (without interference) was obtained for the wave field of longitudinal waves in a layered (discrete) ball of planetary size. The calculations of the total wave field, rays and travel-time curves of longitudinal waves for the spherical model of the Earth AK135 with a carrier frequency of 1 hertz are presented. The analytical solution showed that at angles smaller than 145 degrees ahead of the PKP‑waves, low-amplitude waves appear, with a higher frequency of about 1,3 hertz. Indeed, these high-frequency oscillations have the form characteristic for waves scattered at a certain object. The ray pattern and the travel-time graph show that these high-frequency oscillations are due to exclusively to the spherical geometry of the Earth. This could be explained by the interference of refracted and reflected longitudinal waves in the bottom of a discrete outer core. This field propagates even further towards smaller angles due to the interference of diffraction waves.

scholarly journals Simulation of High-Frequency Rotational Motion in a Two-Dimensional Laterally Heterogeneous Half-Space

2021 ◽  
Author(s):  
Ivan Lokmer ◽  
Varun Kumar Singla ◽  
John McCloskey
Keyword(s):  
Wave Field ◽  
Half Space ◽  
High Frequency ◽  
Body Waves ◽  
Propagation Path ◽  
Small Scale ◽  
Two Dimensional ◽  
Engineering Structures ◽  
Background Medium ◽  
Body Forces

<p>The seismic waves responsible for vibrating civil engineering structures undergo interference, focusing, scattering, and diffraction by the inhomogeneous medium encountered along the source-to-site propagation path. The subsurface heterogeneities at a site can particularly alter the local seismic wave field and amplify the ground rotations, thereby increasing the seismic hazard. The conventional techniques to carry out full wave field simulations (such as finite-difference or spectral finite element methods) at high frequencies (e.g., 15 Hz) are computationally expensive, particularly when the size of the heterogeneities is small (e.g., <100 m). This study proposes an alternative technique that is based on the first-order perturbation theory for wave propagation. In this technique, the total wave field due to a particular source is obtained as a superposition of the ‘mean’ and ‘scattered’ wave fields. Whereas the ‘mean’ wave field is the response of the background (i.e., heterogeneity-free) medium due to the given source, the ‘scattered’ wave is the response of the background medium excited by fictitious body forces. For a two-dimensional laterally heterogeneous elastic medium, these body forces can be conveniently evaluated as a function of the material properties of the heterogeneities and the mean wave field. Since the problem of simulating high-frequency rotations in a laterally heterogeneous medium reduces to that of calculating rotations in the background medium subjected to the (1) given seismic source and (2) body forces that mathematically replace the small-scale heterogeneities, the original problem can be easily solved in a computationally accurate and efficient manner by using the classical (analytical) wavenumber-integration method. The workflow is illustrated for the case of a laterally heterogenous layer embedded in a homogeneous half-space excited by plane body-waves.</p>

Refined karst feature and fault identification through integrated wave field separation and imaging of Diffraction energy

2021 ◽  
Author(s):  
R. Alay
Keyword(s):  
Wave Field ◽  
Water Environment ◽  
Fault Identification ◽  
Small Scale ◽  
Advantages And Disadvantages ◽  
Specular Reflections ◽  
Total Wave ◽  
Karst Feature ◽  
Wave Field Separation ◽  
Field Separation

In this abstract, a case study from offshore Indonesia is showcased with examples emphasizing integrated wave field separation methods with the objective of diffraction imaging towards refined karst feature and fault identification. For imaging optimally all diffraction energy, pre-migration and post-migration methods have been integrated. The dataset and examples in this abstract are in a complex geological setting in a very shallow water environment, with a subsurface that is characterized by large carbonate pinnacles containing large amount of karst features with thinning and thickening carbonate layers. For the purpose of refined imaging of diffraction energy only, the total wave field has been separated into specular reflections and diffractions prior to migration and these have been integrated with existing post-migration wave field separation methods. Both the pre-migration and post-migration wave field separation methods have their advantages and disadvantages and is discussed later in this abstract. Diffraction energy, in general is much lower in amplitude than the specular reflections and separately imaging these, unveils higher resolution small scale geological features such as karst features and faults complementing the total wave field PSDM data. With existing industry available methods applying wave field separation in either pre-migration or post-migration stage, limitations have been observed, and therefore we propose in this abstract to integrate both methods and take advantage of the improvements showcased with examples throughout the abstract.

scholarly journals Spontaneous inertia-gravity-wave generation by surface-intensified turbulence

2012 ◽  
Vol 699 ◽  
pp. 153-173 ◽  
Author(s):  
E. Danioux ◽  
J. Vanneste ◽  
P. Klein ◽  
H. Sasaki
Keyword(s):  
Wave Field ◽  
Large Scale ◽  
Spatial Scales ◽  
Baroclinic Instability ◽  
Small Scale ◽  
Random Wave ◽  
Spontaneous Generation ◽  
Thin Filaments ◽  
Random Wave Field ◽  
Omega Equation

AbstractThe spontaneous generation of inertia-gravity waves (IGWs) by surface-intensified, nearly balanced motion is examined using a high-resolution simulation of the primitive equations in an idealized oceanic configuration. At large scale and mesoscale, the dynamics, which is driven by baroclinic instability near the surface, is balanced and qualitatively well described by the surface quasi-geostrophic model. This however predicts an increase of the Rossby number with decreasing spatial scales and, hence, a breakdown of balance at small scale; the generation of IGWs is a consequence of this breakdown. The wave field is analysed away from the surface, at depths where the associated vertical velocities are of the same order as those associated with the balanced motion. Quasi-geostrophic relations, the omega equation in particular, prove sufficient to separate the IGWs from the balanced contribution to the motion. A spectral analysis indicates that the wave energy is localized around dispersion relation for free IGWs, and decays only slowly as the frequency and horizontal wavenumber increase. The IGW generation is highly intermittent in time and space: localized wavepackets are emitted when thin filaments in the surface density are formed by straining, leading to large vertical vorticity and correspondingly large Rossby numbers. At depth, the IGW field is the result of a number of generation events; away from the generation sites it takes the form of a relatively homogeneous, apparently random wave field. The energy of the IGW field generated spontaneously is estimated and found to be several orders of magnitude smaller than the typical IGW energy in the ocean.

Full‐wave acoustic logging in an irregular borehole

Geophysics ◽  
1989 ◽  
Vol 54 (6) ◽  
pp. 758-765 ◽  
Author(s):  
Michel Bouchon ◽  
Denis P. Schmitt
Keyword(s):  
Wave Field ◽  
Boundary Integral ◽  
Borehole Diameter ◽  
Borehole Wall ◽  
Source Distribution ◽  
Small Scale ◽  
Stoneley Wave ◽  
Linear System Of Equations ◽  
Integral Equation Formulation ◽  
Elastic Rock

A new boundary integral equation formulation for wave propagation in a borehole of irregular cross‐section represents the wave field diffracted at the borehole‐rock interface by the radiation from a distribution of surface sources applied along the borehole wall. The wave fields in the borehole fluid and in the elastic rock are then expressed using the discrete wavenumber method. Application of boundary conditions at discretized locations along the borehole wall leads to a linear system of equations, whose inversion yields the required source distribution. We have used the method to investigate the effect of changes in borehole diameter on the pressure wave field inside the borehole. When the change is smooth, records obtained ahead of the discontinuity location are not affected by its presence. In the case of a steep variation, however, a significant amount of the Stoneley‐wave energy is reflected. When the borehole diameters are different at the source and receiver levels, the microseismograms obtained are somewhat of an average of those that would have been recorded in constant‐radius source and receiver boreholes, respectively. Small‐scale fluctuations in borehole diameter decrease the velocity of the Stoneley wave and of the pseudo‐Rayleigh wave.

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