Model‐based removal of water‐layer multiple reflections

Geophysics ◽  
1999 ◽  
Vol 64 (6) ◽  
pp. 1816-1827 ◽  
Author(s):  
Guochun Lu ◽  
Bjørn Ursin ◽  
Jan Lutro
Keyword(s):  
Water Layer ◽  
Computationally Efficient ◽  
Multiple Reflections ◽  
Model Based ◽  
The North ◽  
Sea Bottom ◽  
Receiver Array ◽  
Sea Bed ◽  
Reflectivity Function ◽  
Calculated Amplitude

We have developed a procedure to attenuate water‐layer multiple reflections. We estimate the sea‐bottom reflectivity function and use it plus calculated amplitude functions to model all order water‐layer multiple reflections, taking into account both amplitude and waveform shape. We model the primary and multiple reflections from the sea bottom in the frequency‐slowness domain. The amplitude function in the data modeling includes the source directivity function, source ghost response, receiver array directivity function, receiver ghost response, and offset‐dependent geometrical spreading. For small offsets we can assume that the seabed reflectivity depends only on frequency, and it is estimated using a least‐squares algorithm. An unknown scaling constant in the data is estimated using the amplitude of the primary and first multiple reflection from the sea bed. The composite sea‐bottom reflectivity is estimated as a function of frequency for each common midpoint (CMP) position. We apply the algorithm to high‐resolution seismic data from the North Sea. The modelled data match the recorded data well, and the estimated primary reflectivity is more geologically meaningful than the stacked trace. By comparison with Radon transform multiple removal applied to the same data, the model‐based method was more computationally efficient and left less residual multiple energy.

A two‐layer stacking procedure to enhance converted waves

Geophysics ◽  
1993 ◽  
Vol 58 (7) ◽  
pp. 997-1001 ◽  
Author(s):  
B. L. N. Kennett
Keyword(s):  
Lower Layer ◽  
Effective Means ◽  
Water Layer ◽  
Physical Models ◽  
S Wave ◽  
P Waves ◽  
S Waves ◽  
Receiver Array ◽  
Sea Bed ◽  
Layer Stacking

For marine seismic sources quite efficient conversion of P‐waves to S‐waves can occur at hard seafloors, e.g., carbonate horizons in tropical waters. The S‐waves are reflected back from structures at depth and are reconverted to P‐waves in the water before detection by the receiver array. Such PSSP reflections can carry useful information on the structure beneath the sea bed but are most significant at large offsets and so are not easily stacked with a conventional normal moveout (NMO) procedure based on a hyperbolic time trajectory. A two‐layer stacking procedure that separates the water layer from the region below the seafloor provides a very effective means of extracting the PSSP arrivals, but also works well for P‐waves. There is no direct analytic form for the stacking trajectories but they can be calculated quite efficiently numerically. A further advantage is that the stacking velocity for S‐waves in the lower layer can be interpreted directly in terms of S‐wave propagation, so that S‐wave interval velocities can be found. Stacking procedures based on such simple physical models are likely to be useful in other cases where attention needs to be focused on a particular aspect of the wavefield.

scholarly journals Geology of outer Horns Rev, Danish North Sea

2008 ◽  
Vol 15 ◽  
pp. 41-44
Author(s):  
Jørn Bo Jensen ◽  
Peter Gravesen ◽  
Steen Lomholt
Keyword(s):  
North Sea ◽  
Wind Farm ◽  
Offshore Wind ◽  
Side Scan Sonar ◽  
Cone Penetration Tests ◽  
The North ◽  
Complex Information ◽  
Sea Bottom ◽  
Sea Bed ◽  
The North Sea

In 2006, Dong Energy initiated the development of the Horns Rev II offshore wind farm in the North Sea (Fig. 1). In order to evaluate and map the characteristics of the surface features of the sea bed and to characterise the subsurface in the wind farm area, the Geological Survey of Denmark and Greenland (GEUS) conducted a geophysical survey of the area. The survey utilised a variety of instruments: sparker, side-scan sonar, marine caesium magnetometer and a multibeam echo-sounder. In addition, information on the subsurface sediments was obtained by cone penetration tests (CPT) and by drilling to 30–50 m below the sea bottom. Geological correlation of the CPT results with the other survey results was extremely complicated but was required in order to understand the architecture of the ice marginal glaciotectonic complex. Information on the geology is crucial for evaluation of the geotechnical problems of the region.

The Thirty-Ninth Thomas Lowe Gray Lecture: Offshore Drilling, with Particular Reference to the North Sea and the ‘Sea Quest’

1966 ◽  
Vol 181 (1) ◽  
pp. 848-875 ◽  
Author(s):  
R. G. S. Avery
Keyword(s):  
North Sea ◽  
Essential Factor ◽  
Safety Equipment ◽  
Offshore Drilling ◽  
Advantages And Disadvantages ◽  
The North ◽  
Drilling Equipment ◽  
Sea Bed ◽  
Weight Problems ◽  
The North Sea

The origins of offshore drilling work and the development of structures used at sea are traced. Comparison of the various types illustrates the advantages and disadvantages of each. Tables show the numbers in operation, being built, and the apparent liability of each type to damage. Typical bore-hole structures are illustrated, the need for undersea well-heads explained and their development into a sea-bed completion is discussed. Much more research is necessary before this can be considered a practical proposition. The design of drilling barge equipment is compared with typical land rigs and the development of drilling equipment, including the sophisticated electric drive and turbo-drill, discussed. Rigs in various types of barge are compared. Fire precautions and other safety equipment are described. The problems associated with control by the driller lead to complications of motive power layout. The lecture describes in some detail the design of the semi-submersible drilling barge Sea Quest, illustrates the weight problems and their effect on floating stability and indicates the need for management decisions on the degree of resistance to damage. This is measured by the variable deck load of drilling equipment that can be held on board and the degree of weather deterioration that can be tolerated before disengaging the drill from the hole. The need for, and extent of, diving is discussed, with some comparison between diving vehicles. Weather too is an essential factor of work in the North Sea and both pre-surveys and day-to-day reporting are described.

The onset of the early Toarcian flooding of the Pliensbachian carbonate platform of Central Tunisia (North-South Axis) as inferred from trace fossils and geochemistry

2021 ◽  
pp. SP514-2021-10
Author(s):  
Matías Reolid ◽  
Mohamed Soussi ◽  
Jesús Reolid ◽  
Wolfgang Ruebsam ◽  
Ilef Belhaj Taher ◽  
...  
Keyword(s):  
Carbonate Platform ◽  
High Energy ◽  
Trace Fossils ◽  
Energy Conditions ◽  
Local Conditions ◽  
Content Type ◽  
The North ◽  
Sea Bottom ◽  
Supplementary Material ◽  
South Axis

AbstractThe flooding of the Lower Jurassic shelf in the North Gondwana Palaeomargin during the early Toarcian occurred on a fragmented and irregular topography affected by differential subsidence—due to the activity of listric faults along the North-South Axis of Tunisia—that favoured lateral changes in facies and thickness at a kilometric scale. The onset of Toarcian sedimentation (Polymorphum ammonite Zone, NJT5c nannofossil Subzone) in two adjacent sections was characterised by the deposition of limestones under high-energy conditions. The Châabet El Attaris section was located in a depressed sub-basin, and recorded restricted environmental conditions owing to water stagnation and an oxygen-depleted sea-bottom. Therefore, dark mudstones developed, with increased TOC contents and enhanced accumulation of redox-sensitive elements. The sedimentation of limestones bearing gutter cast structures is related to gravity flows probably linked to storm activities. These processes favoured the remobilization of sediments at the sea floor, as well as oxygen input to bottom waters, as shown by the record of trace fossils including Zoophycos, Ophiomorpha, and secondarily, Chondrites and Diplocraterion. The thinly interbedded dark mudstones are locally rich in thin-shelled bivalves that re-colonised the sea bottom after the sedimentation of these high-energy deposits, and subsequently underwent mass mortality related to the return of oxygen-depleted conditions. The Kef El Hassine section is located in the upper part of a tilted, less subsident block, as indicated by its reduced thickness compared with the Châabet El Attaris section; the absence of dark mudstones implies oxic conditions. The Polymorphum Zone consists of limestones showing evidence of sedimentation under high-energy conditions, along with hardgrounds. The occurrence of Zoophycos (deep-tiers) in the upper part of some limestone beds of the Polymorphum Zone is linked to minor erosive processes. The top of the high-energy sequence—below the deposits of a marly interval corresponding to the Levisoni Zone—is interpreted as a hardground given the high content of belemnites and Arenicolites, some of them boring on the eroded Zoophycos and Thalassinoides. This study shows that the sedimentary expression of the Jenkyns Event is not uniform across Tunisia, supporting the importance of local conditions in determining the development of anoxic conditions.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5510162

scholarly journals Performance and Economic Assessment of a Grid-Connected Photovoltaic Power Plant with a Storage System: A Comparison between the North and the South of Italy

Energies ◽  
2019 ◽  
Vol 12 (12) ◽  
pp. 2356 ◽  
Author(s):  
Ferdinando Chiacchio ◽  
Fabio Famoso ◽  
Diego D’Urso ◽  
Luca Cedola
Keyword(s):  
Power Plant ◽  
Power Plants ◽  
Low Voltage ◽  
Storage System ◽  
Economic Feasibility ◽  
The South ◽  
Model Based ◽  
The North ◽  
Photovoltaic Power ◽  
Historical Series

Grid-connected low voltage photovoltaic power plants cover most of the power capacity installed in Italy. They offer an important contribution to the power demand of the utilities connected but, due to the nature of the solar resource, the night-time consumption can be satisfied only withdrawing the energy by the national grid, at the price of the energy distributor. Thanks to the improvement of storage technologies, the installation of a system of battery looks like a promising solution by giving the possibility to increase auto-consumption dramatically. In this paper, a model-based approach to analyze and discuss the performance and the economic feasibility of grid-connected domestic photovoltaic power plants with a storage system is presented. Using as input to the model the historical series (2008–2017) of the main ambient variables, the proposed model, based on Stochastic Hybrid Fault Tree Automaton, allowed us to simulate and compare two alternative technical solutions characterized by different environmental conditions, in the north and in the south of Italy. The performances of these systems were compared and an economic analysis, addressing the convenience of the storage systems was carried out, considering the characteristic useful-life time, 20 years, of a photovoltaic power plant. To this end the Net Present Value and the payback time were evaluated, considering the main characteristics of the Italian market scenario.

scholarly journals A Case Study of Digital Elevation Model-Based Slope Stability Assessment on Managed Forestland in the Oregon Coast Range

2006 ◽  
Vol 21 (4) ◽  
pp. 195-202
Author(s):  
Marvin R. Pyles ◽  
Mari Kramer
Keyword(s):  
Slope Stability ◽  
Digital Elevation Model ◽  
Low Risk ◽  
Correct Prediction ◽  
Stability Assessment ◽  
Forest Management Planning ◽  
Model Based ◽  
The North ◽  
Digital Elevation ◽  
Elevation Model

Abstract An aerial photo-based inventory of landslides on recently harvested and reforested land after a significant landslide-producing storm in February 1996, was compared with a digital elevation model-based assessment of slope stability (shallow landsliding stability model [SHALSTAB]) for Confederated Tribes of Siletz Indians (CTSI) and surrounding forestland. The SHALSTAB predictions of landslide locations did not correlate well with the locations of observed landslides. Eighty-nine percent of the landslides on the more stable landform in the southern portion of the CTSI ownership occurred on land that SHALSTAB indicated to be at a low risk of landsliding. Seventy-two percent of the landslides on the less stable landform to the north occurred on land that SHALSTAB indicated to be at a low risk of landsliding. Conversely, only 11 and 28%, respectively, of the observed landslides occurred on lands predicted to be “chronically unstable” or at “high risk” by SHALSTAB. This level of correct prediction of landsliding was judged to be unacceptable for SHALSTAB to be used for slope stability assessment as a part of forest management planning. West. J. Appl. For. 21(4):195–202.

scholarly journals Bayesian splines versus fractional polynomials in network meta-analysis

2020 ◽  
Vol 20 (1) ◽  
Author(s):  
Andreas Heinecke ◽  
Marta Tallarita ◽  
Maria De Iorio
Keyword(s):  
Meta Analysis ◽  
Indirect Comparison ◽  
Real Data ◽  
Multiple Time ◽  
Computationally Efficient ◽  
Fractional Polynomials ◽  
Time Points ◽  
Model Based ◽  
Multiple Treatments ◽  
Indirect Comparisons

Abstract Background Network meta-analysis (NMA) provides a powerful tool for the simultaneous evaluation of multiple treatments by combining evidence from different studies, allowing for direct and indirect comparisons between treatments. In recent years, NMA is becoming increasingly popular in the medical literature and underlying statistical methodologies are evolving both in the frequentist and Bayesian framework. Traditional NMA models are often based on the comparison of two treatment arms per study. These individual studies may measure outcomes at multiple time points that are not necessarily homogeneous across studies. Methods In this article we present a Bayesian model based on B-splines for the simultaneous analysis of outcomes across time points, that allows for indirect comparison of treatments across different longitudinal studies. Results We illustrate the proposed approach in simulations as well as on real data examples available in the literature and compare it with a model based on P-splines and one based on fractional polynomials, showing that our approach is flexible and overcomes the limitations of the latter. Conclusions The proposed approach is computationally efficient and able to accommodate a large class of temporal treatment effect patterns, allowing for direct and indirect comparisons of widely varying shapes of longitudinal profiles.

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