Stereotomography assisted by migration of attributes     

Sylvain Nguyen †  Reda Baina  Mathias Alerini ‡  Gilles Lambaré  Vincent Devaux  Mark Noble 《Geophysical Prospecting》2008,56(5):613-625

Depth velocity model building remains a difficult step within the seismic depth imaging sequence. Stereotomography provides an efficient solution to this problem but was limited until now to a picking of seismic data in the prestack time un-migrated domain. We propose here a method for stereotomographic data picking in the depth migrated domain. Picking in the depth migrated domain exhibits the advantage of a better signal-to-noise ratio and of a more regular distribution of picked events in the model, leading to a better constrained tomographic inverse problem. Moreover, any improvement on the velocity model will improve the migrated results, again leading to improved picking. Our strategy for obtaining a stereotomographic dataset from a prestack depth migration is based on migration of attributes (and not on a kinematic demigration approach!). For any locally coherent event in the migrated image, migration of attributes allows one to compute ray parameter attributes corresponding to the specular reflection angle and dip. For application to stereotomography, the necessary attributes are the source/receiver locations, the traveltime and the data slopes. For the data slope, when the migration velocity model is erroneous, some additional corrections have to be applied to the result of migration of the attributes. Applying these corrections, our picking method is theoretically valid whatever the quality of the migration velocity model. We first present the theoretical aspects of the method and then validate it on 2D synthetic and real seismic reflection data sets.  相似文献   

The critical period of high mortality of larvae fish —A discussion based on current research     

Li Sifa  J. A. Mathias 《中国海洋湖沼学报》1987,5(1):80-96

Most fishes suffer high mortality during early development stages. The existence of a “critical period” was hypothesized by Hjort (1914). However, several decades of research have resulted in considerable controversy over the hypothesis. This paper attempts to clarify the critical period concept, demonstrate its usefulness, and resolve some of the controversy surrounding it. Based on our own studies and the literature, we find that within the “aquaculture school” (those concerned with culturing fishes, particulary larval stages), there is a great deal of evidence for the critical period concept. But we redefine the concept of “critical period” of mortality of fish larvae in this way. The deepest, sharpest, and fastest physiological and ecological changes during the development of the larvae are produced with the shift from endogenous nutrition to exogenous. At this stage, the old functions are quickly being replaced by new functions inside the body. Because of this shifting of function and imperfection of organs, the larvae are most sensitive at this time to environmental factors, particularly food supply. A higher specific mortality rate often occurs immediately folowing the period of strictly endogenous yolk feeding, and during the period of first exogenous feeding. Then it may be followed by a lower specific mortality rate. The significance of a “critical period” for fish populations is discussed. A good understanding of the “critical period” would provide a means for predicting the strength of year classes in natural fish populations, and also suggests approaches for increasing survival in aquaculture systems.  相似文献   

Stable isotope study of cave percolation waters in subtropical Brazil: Implications for paleoclimate inferences from speleothems     

Francisco W. Cruz  Jr.  Ivo Karmann  Oduvaldo Viana  Jr.  Stephen J. Burns  Jos A. Ferrari  Mathias Vuille  Alcides N. Sial  Marcelo Z. Moreira 《Chemical Geology》2005,220(3-4):245-262

We analyze the interannual monthly variability of oxygen isotope ratios in data from IAEA stations along the Atlantic coast of South America between 23° and 34° S to evaluate the influence of parameters such as temperature, rainfall amount and moisture source contribution on meteoric water recharging two karst systems in subtropical Brazil. In addition, a 2 year monitoring program performed on soil and cave drip and rimstone pool waters from sampling sites with contrasting discharge values and located at 100 and 300 m below the surface in the Santana Cave System (24°31′ S; 48°43′ W), is used to test the influence of hydrologic and geologic features on the temporal variations of seepage water δ¹⁸O.

Interannual monthly variations in δ¹⁸O of rainfall reflect primarily regional changes in moisture source contribution related to seasonal shifts in atmospheric circulation from a more monsoonal regime in summer (negative values of δ¹⁸O) to a more extratropical regime in winter (positive values of δ¹⁸O). Variations in groundwater δ¹⁸O indicate that the climatic signal of recent rainfall events is rapidly transmitted through the relatively deep karst aquifer to the cave drip waters, regardless of location of collection in the cave. In addition, the data also suggest that water replenishment in the system is triggered by the increase in hydraulic head during periods when recharge exceeds the storage capacity of the soil and epikarst reservoirs. Significant perturbations in the groundwater composition, characterized by more positive values of δ¹⁸O, are probably connected to an increased Atlantic moisture contribution associated with extratropical precipitation. This implies that the δ¹⁸O of speleothems from caves in this region may be a suitable proxy for studying tropical–extratropical interactions over South America, a feature that is intrinsically related to the global atmospheric circulation.  相似文献   

The significance of flow in the matrix of the Chalk unsaturated zone     

S.A. Mathias  A.P. Butler  N. McIntyre  H.S. Wheater 《Journal of Hydrology》2005,310(1-4):62-77

The significance of flow in the matrix of the Chalk unsaturated zone, in comparison with flow in fractures, has been the subject of much debate. In this article, important elements of the literature are discussed in detail and several simple modelling analyses based on steady-state flow are presented. A study of the sensitivity of solute spreading to fracture spacing in models that ignore matrix flow shows that this latter assumption is generally incompatible with observed solute profiles, unless unrealistically small fracture spacings are assumed. The effect of air phase continuities (e.g. bedding planes) on matrix flow has also been examined. These discontinuities are frequently interrupted by points of connectivity between matrix blocks. An issue therefore is the relationship between connectivity and its effect on inter-block conductance. A simple analysis of the Laplace equation shows that just 1% connectivity represents an effective pathway equivalent to 18% of the local rock hydraulic conductivity. Obviously, when there is no fracture flow, solute spreading is significantly reduced. However, dual permeability model simulations show that matrix flow reduces solute spreading in the presence of persistent fracture flow. All of the above studies suggest that flow in the matrix of the Chalk unsaturated zone is significant and that ignoring it may result in a serious misunderstanding of the system.  相似文献   

Multiple Well Systems with Non‐Darcy Flow     

Ana Mijic  Simon A. Mathias  Tara C. LaForce 《Ground water》2013,51(4):588-596

Optimization of groundwater and other subsurface resources requires analysis of multiple‐well systems. The usual modeling approach is to apply a linear flow equation (e.g., Darcy's law in confined aquifers). In such conditions, the composite response of a system of wells can be determined by summating responses of the individual wells (the principle of superposition). However, if the flow velocity increases, the nonlinear losses become important in the near‐well region and the principle of superposition is no longer valid. This article presents an alternative method for applying analytical solutions of non‐Darcy flow for a single‐ to multiple‐well systems. The method focuses on the response of the central injection well located in an array of equally spaced wells, as it is the well that exhibits the highest pressure change within the system. This critical well can be represented as a single well situated in the center of a closed square domain, the width of which is equal to the well spacing. It is hypothesized that a single well situated in a circular region of the equivalent plan area adequately represents such a system. A test case is presented and compared with a finite‐difference solution for the original problem, assuming that the flow is governed by the nonlinear Forchheimer equation.  相似文献   

Joint optimization of oil well placement and controls     

Mathias C. Bellout  David Echeverría Ciaurri  Louis J. Durlofsky  Bjarne Foss  Jon Kleppe 《Computational Geosciences》2012,16(4):1061-1079

Well placement and control optimization in oil field development are commonly performed in a sequential manner. In this work, we propose a joint approach that embeds well control optimization within the search for optimum well placement configurations. We solve for well placement using derivative-free methods based on pattern search. Control optimization is solved by sequential quadratic programming using gradients efficiently computed through adjoints. Joint optimization yields a significant increase, of up to 20% in net present value, when compared to reasonable sequential approaches. The joint approach does, however, require about an order of magnitude increase in the number of objective function evaluations compared to sequential procedures. This increase is somewhat mitigated by the parallel implementation of some of the pattern-search algorithms used in this work. Two pattern-search algorithms using eight and 20 computing cores yield speedup factors of 4.1 and 6.4, respectively. A third pattern-search procedure based on a serial evaluation of the objective function is less efficient in terms of clock time, but the optimized cost function value obtained with this scheme is marginally better.  相似文献   

A case for hornblende dominated fractionation of arc magmas: the Chelan Complex (Washington Cascades)   总被引：5，自引：3，他引：2  

Mathias Dessimoz  Othmar Müntener  Peter Ulmer 《Contributions to Mineralogy and Petrology》2012,163(4):567-589

Amphibole fractionation in the deep roots of subduction-related magmatic arcs is a fundamental process for the generation of the continental crust. Field relations and geochemical data of exposed lower crustal igneous rocks can be used to better constrain these processes. The Chelan Complex in the western U.S. forms the lowest level of a 40-km thick exposed crustal section of the North Cascades and is composed of olivine websterite, pyroxenite, hornblendite, and dominantly by hornblende gabbro and tonalite. Magmatic breccias, comb layers and intrusive contacts suggest that the Chelan Complex was build by igneous processes. Phase equilibria, textural observations and mineral chemistry yield emplacement pressures of ∼1.0 GPa followed by isobaric cooling to 700°C. The widespread occurrence of idiomorphic hornblende and interstitial plagioclase together with the lack of Eu anomalies in bulk rock compositions indicate that the differentiation is largely dominated by amphibole. Major and trace element modeling constrained by field observations and bulk chemistry demonstrate that peraluminous tonalite could be derived by removing successively 3% of olivine websterite, 12% of pyroxene hornblendite, 33% of pyroxene hornblendite, 19% of gabbros, 15% of diorite and 2% tonalite. Peraluminous tonalite with high Sr/Y that are worldwide associated with active margin settings can be derived from a parental basaltic melt by crystal fractionation at high pressure provided that amphibole dominates the fractionation process. Crustal assimilation during fractionation is thus not required to generate peraluminous tonalite.  相似文献   

Time‐geographic Derivation of Feasible Co‐presence Opportunities from Network‐constrained Episodic Movement Data     

Mathias Versichele  Tijs Neutens  Manuel Claeys Bouuaert  Nico Van de Weghe 《Transactions in GIS》2014,18(5):687-703

Certain datasets on moving objects are episodic in nature – that is, the data is characterized by time gaps during which the position of the object is unknown. In this article, a model is developed to study the sparsely sampled network‐constrained movement of several objects by calculating both potential and feasible (i.e. more likely) co‐presence opportunities over time. The approach is applied to the context of a static sensor network, where the location of an object is only registered when passing a sensor location along a road network. Feasibility is incorporated based on the deviation from the shortest path. As an illustration, the model is applied to a large Bluetooth tracking dataset gathered at a mass event. The model output consists of maps showing the temporal evolution of the distribution of feasible co‐presence opportunities of tracked visitors over the network (i.e. the number of visitors that could have been present together). We demonstrate the model's usefulness in studying the movement and distribution of a crowd over a study area with relatively few sampling locations. Finally, we discuss the results with a special emphasis on the distinction between feasible and actual presence, the need for further validation and calibration, and the performance of the implementation.  相似文献   

Homogeneous reprocessing of GPS,GLONASS and SLR observations   总被引：3，自引：2，他引：1  

Mathias Fritsche  Krzysztof Sośnica  Carlos Javier Rodríguez-Solano  Peter Steigenberger  Kan Wang  Reinhard Dietrich  Rolf Dach  Urs Hugentobler  Markus Rothacher 《Journal of Geodesy》2014,88(7):625-642

The International GNSS Service (IGS) provides operational products for the GPS and GLONASS constellation. Homogeneously processed time series of parameters from the IGS are only available for GPS. Reprocessed GLONASS series are provided only by individual Analysis Centers (i. e. CODE and ESA), making it difficult to fully include the GLONASS system into a rigorous GNSS analysis. In view of the increasing number of active GLONASS satellites and a steadily growing number of GPS+GLONASS-tracking stations available over the past few years, Technische Universität Dresden, Technische Universität München, Universität Bern and Eidgenössische Technische Hochschule Zürich performed a combined reprocessing of GPS and GLONASS observations. Also, SLR observations to GPS and GLONASS are included in this reprocessing effort. Here, we show only SLR results from a GNSS orbit validation. In total, 18 years of data (1994–2011) have been processed from altogether 340 GNSS and 70 SLR stations. The use of GLONASS observations in addition to GPS has no impact on the estimated linear terrestrial reference frame parameters. However, daily station positions show an RMS reduction of 0.3 mm on average for the height component when additional GLONASS observations can be used for the time series determination. Analyzing satellite orbit overlaps, the rigorous combination of GPS and GLONASS neither improves nor degrades the GPS orbit precision. For GLONASS, however, the quality of the microwave-derived GLONASS orbits improves due to the combination. These findings are confirmed using independent SLR observations for a GNSS orbit validation. In comparison to previous studies, mean SLR biases for satellites GPS-35 and GPS-36 could be reduced in magnitude from \(-35\) and \(-38\)  mm to \(-12\) and \(-13\)  mm, respectively. Our results show that remaining SLR biases depend on the satellite type and the use of coated or uncoated retro-reflectors. For Earth rotation parameters, the increasing number of GLONASS satellites and tracking stations over the past few years leads to differences between GPS-only and GPS+GLONASS combined solutions which are most pronounced in the pole rate estimates with maximum 0.2 mas/day in magnitude. At the same time, the difference between GLONASS-only and combined solutions decreases. Derived GNSS orbits are used to estimate combined GPS+GLONASS satellite clocks, with first results presented in this paper. Phase observation residuals from a precise point positioning are at the level of 2 mm and particularly reveal poorly modeled yaw maneuver periods.  相似文献   

Ultrasonic attenuation of pure tetrahydrofuran hydrate          下载免费PDF全文

Mathias Pohl  Manika Prasad  Michael L. Batzle 《Geophysical Prospecting》2018,66(7):1349-1357

Improved estimates of the amount of subsurface gas hydrates are needed for natural resource, geohazard, and climate impact assessments. To evaluate gas hydrate saturation from seismic methods, the properties of pure gas hydrates need to be known. Whereas the properties of sediments, specifically sands, and hydrate‐bearing sediments are well studied, the properties of pure hydrates are largely unknown. Hence, we present laboratory ultrasonic P‐wave velocity and attenuation measurements on pure tetrahydrofuran hydrates as they form with reducing temperatures from 25°C to 1°C under atmospheric pressure conditions. Tetrahydrofuran hydrates, with structure II symmetry, are considered as proxies for the structure I methane hydrates because both have similar effects on elastic properties of hydrate‐bearing sediments. We find that although velocity increased, the waveform frequency content and amplitude decreased after the hydrate formation reaction was complete, indicating an increase in P‐wave attenuation after hydrate formation. When the tetrahydrofuran hydrate was cooled below the freezing point of water, velocity and quality factor increased. Nuclear Magnetic Resonance results indicate the presence of water in the “pure hydrate” samples above the water freezing point, but none below. The presence of liquid water between hydrate grains most likely causes heightened attenuation in tetrahydrofuran hydrates above the freezing point of water. In naturally occurring hydrates, a similarly high attenuation might relate to the presence of water.  相似文献