Phase inversion deconvolution for long and short period multiples attenuationl1     

Eugene Lichrnan  E. John Northwood 《Geophysical Prospecting》1995,43(4):469-486

A new approach to deconvolution has been developed to improve the attenuation of multiple energy. This approach to deconvolution is unique in that it not only eliminates the usual assumptions of a minimum phase lag wavelet and a random distribution of impulses, but also overcomes the noise limitation of the homomorphic deconvolution and its inherent instability to phase computation. We attempt to analyse the continuous alteration of the acoustic waveform during the propagation through a linear system. Based on the results of this analysis, the surface-related measurements are described as a convolution of the impulse response of the system with the non-stationary forward wavelet which includes all multiple terms generated within the system. The amplitude spectrum of the forward wavelet is recovered from the amplitude spectrum of the recorded signal, using the difference between the rate of decay of the source wavelet and the duration of the measurement. The phase spectrum of the forward wavelet is estimated using the Hilbert transform and the fact that the mixed phase lag wavelet can be presented as a convolution of the minimum and maximum phase lag wavelets. The multiples are discriminated from primaries by comparison of the phase spectrum of the seismic signal and the inverse of the forward wavelet. Therefore, the technique is called phase inversion deconvolution (PID). This approach requires no velocity information in order to recognize and attenuate multiple energy. Therefore, primary energy is recovered in the near-offset region where the velocity differential between primary and multiple energies is very small.  相似文献   

Measurements of level-crossing statistics of concentration fluctuations in plumes dispersing in the atmospheric surface layer     

Eugene Yee  R. Chan  P. R. Kosteniuk  G. M. Chandler  C. A. Biltoft  J. F. Bowers 《Boundary-Layer Meteorology》1995,73(1-2):53-90

The statistics of level crossings and local extremes in concentration fluctuations in plumes dispersing in the atmosphere have been investigated. A set of concentration fluctuation tracer experiments has been utilized to measure the statistical propertics of the upcrossing interval (inter-arrival time between consecutive concentration bursts), excursion duration (persistence or width of concentration bursts), and concentration amplitude (difference between the maximum and minimum concentrations between successive upcrossings) with respect to a range of concentration crossing levels. In particular, the effect of downwind distance and atmospheric stratification on the level-crossing statistics has been studied in detail. It is shown that the effect of increasing atmospheric stability on level-crossing statistics is similar to the effect of increasing distance from the source in the sense that level-crossing statistics of concentration fluctuations in stable stratification resemble those in neutral stratification, but at a greater downwind distance. It is also found that the distribution of the interval between consecutive upcrossings of a concentration level, as well as the duration of an excursion across a concentration level, can be approximated by a lognormal distribution, whereas the distribution of the concentration amplitude is best characterized by a gamma distribution. Some implications of these results for the modeling of level-crossing statistics of concentration fluctuations are discussed.  相似文献   

Boundary-layer flow and turbulence near porous obstacles     

Hao Wang  Eugene S. Takle 《Boundary-Layer Meteorology》1995,74(1-2):73-88

We derive a set of governing equations for flow through porous obstacles by employing a two-step averaging processes. The Navier-Stokes equations under the Boussinesq approximation that describe the air space of the porous obstacle are subjected to high-wavenumber a veraging, which leads to a set of high-frequency (wake) turbulence equations. We then use conventional Reynolds-averaging methods to obtain statistically steady mean and turbulence equations that include interactions between wake and shear turbulence. Our method provides a theoretical basis for the cascade of turbulent kinetic energy. We use this approach to analyze the constants and parameters of simpleK-theory and higher-order closure models. We also discuss qualitatively the theory of the turbulence energy generation process and the significance of interactions between different turbulent mechanisms.  相似文献   

Roberts Rift, Canyonlands, Utah, A Natural Hydraulic Fracture Caused by Comet or Asteroid Impact     

Peter W. Huntoon  Eugene M. Shoemaker 《Ground water》1995,33(4):561-569

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Petrogenesis of the Elephant Moraine A79001 meteorite: Multiple magma pulses on the shergottite parent body     

Harry Y. McSween  Eugene Jarosewich 《Geochimica et cosmochimica acta》1983,47(8):1501-1513

The EETA 79001 achondrite consists of two distinct igneous lithologies joined along a planar, non-brecciated contact. Both are basaltic rocks composed primarily of pigeonite, augite, and maskelynite, but one contains zoned megacrysts of olivine, orthopyroxene, and chromite that represent disaggregated xenoliths of harzburzite. Both lithologies probably formed from successive volcanic flows or multiple injections of magma into a small, shallow chamber. Many similarities between the two virtually synchronous magmas suggest that they are related. Possible mechanisms to explain their differences involve varying degrees of assimilation, fractionation from similar parental magmas, or partial melting of a similar source peridotite; of these, assimilation of the observed megacryst assemblage seems most plausible. However, some isotopic contamination may be required in any of these petrogenetic models. The meteorite has suffered extensive shock metamorphism and localized melting during a large impact event that probably excavated and liberated it from its parent body. Both basaltic lithologies and the inferred ultramafic protolith of the megacryst assemblage are petrologically similar to other members of the shergottite group, and all may have been derived from a volcanic-plutonic complex on a planetary body.  相似文献   

Combining InSAR and seismology to study the 2003 Siberian Altai earthquakes—dextral strike-slip and anticlockwise rotations in the northern India–Eurasia collision zone     

Edwin Nissen  Brian Emmerson  Gareth J. Funning  Anatoly Mistrukov  Barry Parsons  David P. Robinson  Eugene Rogozhin  Tim J. Wright † 《Geophysical Journal International》2007,169(1):216-232

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An Analytical Model For Threshold Crossing Rates Of Concentration Fluctuations In Dispersing Plumes     

Eugene Yee 《Boundary-Layer Meteorology》2001,98(3):517-527

A simple analytical model is developed for the meanupcrossing rate of plume concentration fluctuations assuming that thisprocess can be well approximated by a lognormal process. The resultingexpression requires only the specification of the in-plume fluctuationintensity and in-plume Taylor micro-time scale and, hence, does notexplicitly involve the joint probability density function of theconcentration and its derivative. The analytical model provides agood fit to some field measurements of the mean upcrossing rate ina dispersing plume.  相似文献   

Dust in the Wind: Long Range Transport of Dust in the Atmosphere and Its Implications for Global Public and Ecosystem Health   总被引：4，自引：0，他引：4  

Dale W. Griffin  Christina A. Kellogg  Eugene A. Shinn 《Global Change & Human Health》2001,2(1):20-33

Movement of soil particles in atmospheres is a normal planetary process. Images of Martian dust devils (wind-spouts) and dust storms captured by NASA's Pathfinder have demonstrated the significant role that storm activity plays in creating the red atmospheric haze of Mars. On Earth, desert soils moving in the atmosphere are responsible for the orange hues in brilliant sunrises and sunsets. In severe dust storm events, millions of tons of soil may be moved across great expanses of land and ocean. An emerging scientific interest in the process of soil transport in the Earth's atmosphere is in the field of public and ecosystem health. This article will address the benefits and the potential hazards associated with exposure to particle fallout as clouds of desert dust traverse the globe. This revised version was published online in September 2006 with corrections to the Cover Date.  相似文献   

Of manatees, mangroves, and the Mississippi River: Is there an estuarine signature for the Gulf of Mexico?     

R. Eugene Turner 《Estuaries and Coasts》2001,24(2):139-150

Important parameters of estuarine variability include morphology, flushing times, nutrient loading rates, and wetland: water ratios. This variability both reflects and disguises underlying relationships between the physics and biology of estuaries, which this comparative analysis seeks to reveal, using the Gulf of Mexico (GOM) estuaries as a starting point. A question used to focus this analysis is: are the GOM estuaries unique? The GOM receives the Mississippi River, a uniquely large, world-class river, which dominates the freshwater and nutrient inflows to the GOM continental shelf, whose margins include 35 major estuarine systems. These GOM estuaries have 28% and 41% of the U.S. estuarine wetlands and open water, respectively. Within the GOM, estuarine nitrogen, phosphorus, and suspended matter loading varies over 2 orders of magnitude. Anoxic estuarine events tend to occur in estuaries with relatively slow freshwater turnover and high nitrogen loading. Compared to estuaries from other regions in the U.S., the average GOM estuary is distinguished by shallower depths, faster freshwater flushing time, a higher wetland area:open water area ratio, greater fisheries yield per area wetland, lower tidal range, and higher sediment accumulation rates. The average GOM estuary often, but not always, has a flora and fauna not usually found in most other U.S. estuaries (e.g., manatees and mangroves). Coastal wetland loss in the GOM is extraordinarily high compared to other regions and is causally linked to cultural influences. Variations in nutrient loading and population density are very large among and within estuarine regions. This variation is large enough to demonstrate that there are insufficient systematic differences among these estuarine regions that precludes cross-system analyses. There are no abrupt discontinuities among regions in the fisheries yields per wetland area, tidal amplitude and vegetation range, salt marsh vertical accretion rates and organic accumulations, nitrogen retention, or wetland restoration rates. These results suggest that a comparative analysis emphasizing forcing functions, rather than geographic uniqueness, will lead to significant progress in understanding how all estuaries function, are perturbed, and even how they can be restored.  相似文献   

On three-dimensionality of shelterbelt structure and its influences on shelter effects   总被引：5，自引：0，他引：5  

Hao Wang  Eugene S. Takle 《Boundary-Layer Meteorology》1996,79(1-2):83-105

Natural shelterbelts, unlike planar barriers, have a certain width, within which interactions among wind speed, drag force and pressure perturbations create a net sheltering effect. The variations of flow, drag force, permeability, and pressure perturbation for shelterbelts of different widths and different horizontal structures are numerically studied, and their influences on shelter efficiency are discussed. Comparisons are made of fourteen medium-dense shelterbelts, with the same overall leaf-area, that differ only in width or horizontal distribution of leaf-area density. The simulated results are consistent with both field observations and wind-tunnel measurements.The simulations demonstrate that the total drag force of the entire shelterbelt varies little with changes in width and structure. The results also show that shelter distance and the overall average wind speed reduction decrease only by 15–18% as width increases by a factor of 100, and changes even less for different internal structure. However, width greatly affects the location of minimum wind speed, pressure perturbation, and the permeability of shelterbelts. Horizontal changes of wind speed inside the uniform shelterbelts have four different patterns, which depend on shelterbelt width and height. The absolute pressure perturbation significantly decreases with increasing width. A possible cause of the insensitivity of shelter efficiency to width and internal inhomogeneous structure is the compensation between the effects of permeability and pressure perturbation on shelter efficiency.  相似文献