Acquisition design for direct reflectivity and velocity estimation from blended and irregularly sampled data     

Shotaro Nakayama  Gerrit Blacquière  Tomohide Ishiyama 《Geophysical Prospecting》2019,67(8):2127-2146

Blended acquisition along with efficient spatial sampling is capable of providing high-quality seismic data in a cost-effective and productive manner. While deblending and data reconstruction conventionally accompany this way of data acquisition, the recorded data can be processed directly to estimate subsurface properties. We establish a workflow to design survey parameters that account for the source blending as well as the spatial sampling of sources and detectors. The proposed method involves an iterative scheme to derive the survey design leading to optimum reflectivity and velocity estimation via joint migration inversion. In the workflow, we extend the standard implementation of joint migration inversion to cope with the data acquired in a blended fashion along with irregular detector and source geometries. This makes a direct estimation of reflectivity and velocity models feasible without the need of deblending or data reconstruction. During the iterations, the errors in reflectivity and velocity estimates are used to update the survey parameters by integrating a genetic algorithm and a convolutional neural network. Bio-inspired operators enable the simultaneous update of the blending and sampling operators. To relate the choice of survey parameters to the performance of joint migration inversion, we utilize a convolutional neural network. The applied network architecture discards suboptimal solutions among newly generated ones. Conversely, it carries optimal ones to the subsequent step, which improves the efficiency of the proposed approach. The resultant acquisition scenario yields a notable enhancement in both reflectivity and velocity estimation attributable to the choice of survey parameters.  相似文献   

The impact of surface‐wave attenuation on 3‐D seismic survey design          下载免费PDF全文

Tomohide Ishiyama  Gerrit Blacquière  Wim A. Mulder 《Geophysical Prospecting》2017,65(1):86-96

Three‐dimensional seismic survey design should provide an acquisition geometry that enables imaging and amplitude‐versus‐offset applications of target reflectors with sufficient data quality under given economical and operational constraints. However, in land or shallow‐water environments, surface waves are often dominant in the seismic data. The effectiveness of surface‐wave separation or attenuation significantly affects the quality of the final result. Therefore, the need for surface‐wave attenuation imposes additional constraints on the acquisition geometry. Recently, we have proposed a method for surface‐wave attenuation that can better deal with aliased seismic data than classic methods such as slowness/velocity‐based filtering. Here, we investigate how surface‐wave attenuation affects the selection of survey parameters and the resulting data quality. To quantify the latter, we introduce a measure that represents the estimated signal‐to‐noise ratio between the desired subsurface signal and the surface waves that are deemed to be noise. In a case study, we applied surface‐wave attenuation and signal‐to‐noise ratio estimation to several data sets with different survey parameters. The spatial sampling intervals of the basic subset are the survey parameters that affect the performance of surface‐wave attenuation methods the most. Finer spatial sampling will reduce aliasing and make surface‐wave attenuation easier, resulting in better data quality until no further improvement is obtained. We observed this behaviour as a main trend that levels off at increasingly denser sampling. With our method, this trend curve lies at a considerably higher signal‐to‐noise ratio than with a classic filtering method. This means that we can obtain a much better data quality for given survey effort or the same data quality as with a conventional method at a lower cost.  相似文献   

Physical and coupled fully three-dimensional numerical modeling of pressurized bottom outlet flushing processes in reservoirs     

Ousmane Sawadogo  Gerrit R. Basson  Simon Schneiderbauer 《国际泥沙研究》2019,34(5):461-474

Sediment deposition in reservoirs is an important research topic in engineering practice. Reservoir sedimentation has the potential to affect ood levels, drainage for agricultural land, pump station and hydropower operation as well as navigation. This paper describes the development of a coupled fully three-dimensional (3D) numerical model for the prediction of the local sediment ushing scour upstream of the bottom outlet. The presented numerical model solves the Navier-Stokes equations in conjunction with the k- turbulence model which includes both sediment transport and hydrodynamic parameters. The proposed coupled fully 3D numerical model is used to simulate experimental tests based on non-cohesive sediment. The geometric features of the scour hole (temporal and spatial hole devel- opment) upstream of the bottom outlet were reasonably well predicted compared to the experimental data. Furthermore, the velocity eld upstream of the bottom outlet was in good agreement with mea- surements. The proposed numerical model for bottom outlet ushing was, therefore, validated because of its ability to accurately predict the scour hole development during the ushing process. The proposed numerical model can be considered reliable provided that the model is correctly calibrated and set up to re ect the conditions of a particular case study.  相似文献   

Singularity free formulations of the geodetic boundary value problem in gravity-space     

Gerrit Austen  Wolfgang Keller 《Journal of Geodesy》2009,83(7):645-657

The idea of transforming the geodetic boundary value problem into a boundary value problem with a fixed boundary dates back to the 1970s of the last century. This transformation was found by F. Sanso and was named as gravity-space transformation. Unfortunately, the advantage of having a fixed boundary for the transformed problem was counterbalanced by the theoretical as well as practical disadvantage of a singularity at the origin. In the present paper two more versions of a gravity-space transformation are investigated, where none of them has a singularity. In both cases the transformed differential equations are nonlinear. Therefore, a special emphasis is laid on the linearized problems and their relationships to the simple Hotine-problem and to the symmetries between both formulations. Finally, in numerical simulation study the accuracy of the solutions of both linearized problems is studied and factors limiting this accuracy are identified.  相似文献   

Role of land surface parameterizations on modeling cold-pooling events and low-level jets     

Thara V. Prabha  Gerrit Hoogenboom  Tatiana G. Smirnova 《Atmospheric Research》2011,99(1):147-161

Land surface parameterization schemes play a significant role in the accuracy of meso-local scale numerical models by accounting for the exchange of energy and water between the soil and the atmosphere. The role of land surface processes during large-scale cold-pooling events was studied with two land surface schemes (LSMs) in the Advanced Research Weather Forecasting model (ARW). Model evaluation was complex due to the surface and boundary layer interactions at different temporal and spatial scales as revealed by a scale dependent variance analysis. Wavelet analysis was used for the first time to analyze the model errors with specific focus on land surface processes. The ARW model was also evaluated for the formation of a low-level jet (LLJ). It is shown that vertical resolution in the model boundary layer played a significant role in determining the characteristics of LLJ, which influenced the lower boundary layer structure and moisture distribution. The results showed that the simulated low-level jet over southern Georgia was sensitive to the land surface parameterization and led to a significant difference in the boundary layer exchange. The jet shear played a crucial role in the maintenance of turbulence and weak shear caused excessive radiative cooling leading to unrealistic cold pools in the model. The results are important for regional downscaling as the excessive cold pools that are simulated in the model can go unnoticed.  相似文献   

The art of the science: climate forecasts for wildfire management in the southeastern United States     

Carla Roncoli  Norman Breuer  David Zierden  Clyde Fraisse  Kenneth Broad  Gerrit Hoogenboom 《Climatic change》2012,113(3-4):1113-1121

This article illustrates how a wildfire risk forecast evolved iteratively based on stakeholder consultations. An assessment based on phone interviews indicates that such forecasts can assist fire management decisions, such as deployment of human, financial, and material resources and management of forest, timber, and habitats, and public safety. But careful attention to communication, collaboration, and capacity building is key to realizing this potential.  相似文献   

Estimating trends of Atlantic meridional overturning circulation from long-term hydrographic data and model simulations     

Gerrit Lohmann  Helmuth Haak  Johann H. Jungclaus 《Ocean Dynamics》2008,58(2):127-138

The ocean meridional overturning circulation (MOC) plays a central role for the climate in the Atlantic realm. Since scenarios for future climate change indicate a significant reduction of the MOC under global warming, an assessment of variations and trends of the real MOC is important. Using observations at ocean weather ship (OWS) stations and along oceanic sections, we examine the hydrographic information that can be used to determine MOC trends via its signature in water mass properties obtained from model simulations with the climate model ECHAM5/MPI-OM. We show that temperature trends at mid-latitudes provide useful indirect measure of large-scale changes of deep circulation: A mid-depth warming is related to MOC weakening and a cooling to MOC strengthening. Based on our model experiments, we argue that a continuation of measurements at key OWS sites may contribute to a timely detection of a possible future MOC slowdown and to separate the signal from interannual-to-multidecadal MOC variability. The simulations suggest that the subsurface hydrographic information related to MOC has a lower variability than the MOC trend measured directly. Based on our model and the available long-term hydrographic data, we estimate non-significant MOC trends for the last 80 years. For the twenty-first century, however, the model simulations predict a significant MOC decline and accompanied mid-depth warming trend.  相似文献   

Factors influencing the removal of fine non-cohesive sediment by vortex settling basin at small river abstraction works     

Kuria Kiringu  Gerrit Basson 《国际泥沙研究》2021,36(4):501-511

Diverted sediment causes a wide range of problems at small diversion works.The difference in water levels between low flows and floods,low investment capital and presence of cohesive sediment and fine non-cohesive sediment coupled with a requirement for a high level of supply assurance makes the design of such hydraulic structures complex.Vortex settling basins(VSBs)offer a promising alternative to conventional settling structures or hydro-cyclones.In the current study,parameters affecting the trapping of particles>75 mm were numerically investigated using ANSYS Fluent and were validated by physical modeling.It was established that the inlet velocity needs to be maintained at 0.26 m/s,the underflow to inflow ratio should be between 0.05 and 0.10,the cylinder height to cylinder diameter ratio should be greater than 0.5,and the positioning of the inlet pipe to cylinder height ratio should be greater than 0.7,with a cone of slope ratio of 2:1(V:H)and the cylinder diameter to inlet diameter ratio should be 8.2.These parameters form the basic design guidelines for VSB use at small diversion works(<100 L/s duty capacity).  相似文献   

Atmospheric bridge on orbital time scales     

Gerrit?LohmannEmail author 《Theoretical and Applied Climatology》2017,128(3-4):709-718

Large-scale atmospheric patterns are examined on orbital timescales using a climate model which explicitly resolves the atmosphere–ocean–sea ice dynamics. It is shown that, in contrast to boreal summer where the climate mainly follows the local radiative forcing, the boreal winter climate is strongly determined by modulation of circulation modes linked to the Arctic Oscillation/North Atlantic Oscillation (AO/NAO) and the Northern/Southern Annular Modes. We find that during a positive phase of the AO/NAO the convection in the tropical Pacific is below normal. The related atmospheric circulation provides an atmospheric bridge for the precessional forcing inducing a non-uniform temperature anomalies with large amplitudes over the continents. We argue that this is important for mechanisms responsible for multi-millennial climate variability and glacial inception.  相似文献   

Periglacial evidence for a 1.91–1.89 Ga old glacial period at low latitude,Central Sweden     

Gerrit Kuipers  Frank F. Beunk  Frederik M. van der Wateren 《Geology Today》2013,29(6):218-221

Cryoturbation and slump fold‐like sedimentary structures in ca. 1.9 Ga old dacitic metavolcanic sediments in West Bergslagen, Central Sweden, are recognized as a lowland periglacial environment. This type of environment is comparable with present day tundra in Siberia. Ice‐wedge casts and cryoturbation, together with polygonal frost patterns, are typical geomorphological structures above permafrost in this type of environment. The sedimentary environment could be interpreted as periglacial, broadly comparable to present day tundras. Intensive cryoturbation of the formation and close structural analogy with Quaternary ice‐wedges suggests a cold and humid environment. This discovery is corroborated by a previous report of glacial sediments and structures from NW Australia of ca. 1.8 Ga age. Both occurrences developed at low geographical latitudes, at locations far apart in the Late Palaeoproterozoic supercontinent Columbia. Either suggest the existence of a ca. 100 Ma long epoch of extreme, though possibly intermittent glaciations during the ca. 1.4 Ga long ‘Proterozoic gap’ (～2.2–0.77 Ga) from which no convincing glacial deposits were previously known.  相似文献