Azimuthal Sectors Research Articles

Generation of Tunable Necklace-Pattern Solitons in Two-Dimensional Dissipative System

We obtain necklace-pattern solitons (NPSs) from the same-pattern initial Gaussian pulse modulated by alternating azimuthal phase sections (AAPSs) of out-phase based on the two-dimensional (2D) complex Ginzburg-Landau equation with the cubic-quintic nonlinearity. The initial radially symmetrical Gaussian pulse can evolves into general necklace-rings solitons (NRSs). The number and distribution of pearls is tunable by adjusting sections-number and sections-distribution of AAPSs. In addition, we study the linear increased relationship between size of initial pulses and ring-radii of NRSs. Moreover, we predict the number-threshold of pearls in theoretical analysis by using of balance equations for energy and momentum. Final, we extend the research results to obtain arbitrary NPSs, such as elliptical ring, triangular-ring, and pentagonal ring.

P and SH velocity structure in the upper mantle beneath Northeast China: Evidence for a stagnant slab in hydrous mantle transition zone

Using high-dense regional body waves for three deep earthquakes that occurred around Russia–China border, we investigate both S and P wave velocity structures in the mantle transition zone beneath Northeast China and northern part of North China Craton, where the northwestern Pacific plate is imaged to subhorizontally lie above the 660-km discontinuity. We observe an increasing trend of S–P travel time residuals along the epicentral distance within a distance range of 11–16.5°, indicating a velocity anomaly in MTZ. We seek the simplest model that explains the observed broadband waveforms and relative travel times of triplication for a confined azimuth sector. Both SH and P data suggest a ∼140±20km high velocity layer lying above a slightly depressed and broad 660-km discontinuity. Shear velocity reduction of ∼2.5% in the deeper part of the transition zone is required to compensate for the significantly large relative time between AB and CD triplicate branches and the increased trending of S–P travel time residuals as well. The MTZ, as a whole, is featured by low shear velocity and high Vp/Vs ratio. A water-rich mantle transition zone with 0.2–0.4wt% of H2O may account for the discrepancy between the observed Vp and Vs velocity structures. Our result supports the scenario of a viscosity-dominated stagnant slab with an increased thickness of ∼140km, which was caused by the large viscosity contrast between the lower and upper mantles. The addition of water and eastward trench retreat might facilitate stagnation of the subducting Pacific slab beneath Northeast China.

GPS Dropwindsonde and WSR-88D Observations of Tropical Cyclone Vertical Wind Profiles and Their Characteristics

Abstract The characteristics of tropical cyclone vertical wind profiles and their associated wind speed peaks below 1.5 km were examined through the use of a large number of GPS dropwindsondes (GPS sondes) and radar-derived velocity–azimuth display (VAD) profiles. Composite wind profiles were generated to document the mean structure of tropical cyclone vertical wind profiles and their changes with storm-relative position. Composite profiles were observed to change as the radius decreased inward toward the radius of maximum winds. Profiles also varied between three azimuthal sectors. At landfall, wind profiles exhibited changes with radial distance and differences were observed between those within offshore and onshore flow regimes. The observations support a general reduction in boundary layer depth with decreasing radial distance. Wind profiles with peaks at low altitudes were typically confined to radii less than 60 km, near and radially inward from the radius of maximum winds. Wind speed maxima, when scaled by a layer mean wind, decreased in magnitude as the radius decreased. At landfall, composite profiles showed a distinct low-level wind speed maximum in the eyewall region with significant differences between the onshore and offshore flow regimes.

Scanning Doppler Lidar for Input into Short-Term Wind Power Forecasts

Abstract Scanning Doppler lidar is a promising technology for improvements in short-term wind power forecasts since it can scan close to the surface and produce wind profiles at a large distance upstream (15–30 km) if the atmosphere has sufficient aerosol loading and there are no sizable blockages from terrain or large structures. However, successful measurements require a large spatial sampling domain and new estimation algorithms that can perform well in the very weak signal regime. The maximum likelihood (ML) algorithm in the spectral domain and a faster version based on the minimum mean-square-error (MSE) are investigated by numerical simulation and with actual scanning Doppler lidar data from the Lockheed Martin Coherent Technologies WindTracer lidar. In addition, the maximum range can be extended by simultaneous estimation of the wind speed and wind direction from a larger azimuth sector scan if the atmosphere is well behaved. Real-time operation is possible using the spectral data from the WindTracer lidar and a dedicated computer to interface with a data assimilation system. Analysis of the Doppler lidar data in the first few kilometers can be used to extract the turbulence conditions for improvements in real-time wind farm operations.

Teasing out the faults within the Permian Carbonate using an azimuth-rich seismic data – a Thailand case study

SummaryLand seismic data was acquired over a Permian carbonate field with a wide azimuth acquisition template, such that the recorded 3D seismic data is inherently source-to-detector azimuth rich. This geometry allows the data to be subdivided into azimuth sectors, so that stacks of different “illumination” directions can be generated. Subsurface faults and families of fractures are generally better characterized when illuminated normal to their dip, i.e. head on against the faults.The fault and fracture family patterns from each of the sorted shot-to-receiver azimuth sets portray a slightly different illumination of the continuity and development of these faults as shown in time-slices.The paper will describe the azimuth sorting process, followed by the methodology to sharpen the fault pattern within each dataset. The acquisition of seismic data in a wide-azimuth configuration has shown that with appropriate processing, it is possible to illuminate subtle faulting and fractures quite distinctively within the targeted hard rock reservoir.

Time Constants of the Transition between Onset and Decay Reynolds Numbers for the Appearance of Taylor-Couette Flow

We investigate the onset and the decay of Taylor-Couette flow in finite cylinders, and we report the estimated time scales in the azimuthal section of the flow state transition between the super-critical state and the sub-critical state by fitting the numerical result to the solution of the Stuart-Landau equation. The inner cylinder rotates, and the outer cylinder and both end walls of the cylinders are stationary. Near the end walls of the cylinders, the value of the time scale is small. In the inner region, the radial velocity component has a large time scale near the center of the vortices, while the axial velocity component has a large time scale between the vortices.

Spatiotemporal mode structure of nonlinearly coupled drift wave modes

This paper presents full cross-section measurements of drift waves in the linear magnetized plasma of the Mirabelle device. Drift wave modes are studied in regimes of weakly developed turbulence. The drift wave modes develop azimuthal space-time structures of plasma density, plasma potential, and visible light fluctuations. A fast camera diagnostic is used to record visible light fluctuations of the plasma column in an azimuthal cross section with a temporal resolution of 10 μs corresponding approximately to 10% of the typical drift wave period. Mode coupling and drift wave dispersion are studied by spatiotemporal Fourier decomposition of the camera frames. The observed coupling between modes is compared to calculations of nonlinearly coupled oscillators described by the Kuramoto model.

Use of RTM full 3D subsurface angle gathers for subsalt velocity update and image optimization: Case study at Shenzi field

Various reverse time migration (RTM) angle gather generation techniques have been developed to address poor subsalt data quality and multiarrival induced problems in gathers from Kirchhoff migration. But these techniques introduce new problems, such as inaccuracies in 2D subsurface angle gathers and edge diffraction artifacts in 3D subsurface angle gathers. The unique rich-azimuth data set acquired over the Shenzi field in the Gulf of Mexico enabled the generally artifact-free generation of 3D subsurface angle gathers. Using this data set, we carried out suprasalt tomography and salt model building steps and then produced 3D angle gathers to update the subsalt velocity. We used tilted transverse isotropy RTM with extended image condition to generate full 3D subsurface offset domain common image gathers, which were subsequently converted to 3D angle gathers. The angle gathers were substacked along the subsurface azimuth axis into azimuth sectors. Residual moveout analysis was carried out, and ray-based tomography was used to update velocities. The updated velocity model resulted in improved imaging of the subsalt section. We also applied residual moveout and selective stacking to 3D angle gathers from the final migration to produce an optimized stack image.

On the accuracy of Rüger's approximation for reflection coefficients in HTI media: implications for the determination of fracture density and orientation from seismic AVAZ data

We have investigated the accuracy of Rüger's approximation for PP reflection coefficients in HTI media (relative to an exact generalization of Zoeppritz to anisotropy derived by Schoenberg and Protazio) within the context of seismic fracture characterization. We consider the inverse problem of seismic amplitude-versus-angle and azimuth (AVAZ) inversion with respect to fracture density and azimuthal fracture orientation, as well as the forward problem of calculating PP reflection coefficients for different contrasts and anisotropy levels. The T-matrix approach was used to relate the contrast and anisotropy level to the parameters of the fractures (in the case of a single set of vertical fractures). We have found that Rüger's approximation can be used to recover the true fracture density with small uncertainty if, and only if, the fracture density and contrast are significantly smaller than the values that are believed to occur in many practically interesting cases of fractured (carbonate) reservoirs. In one example involving a minimal contrast and a fracture density in the range 0.05–0.1, Rüger's approximation performed satisfactorily for inversion, although the forward modelling results were not very accurate at high incident angles. But for fracture densities larger than 0.1 (which we believe may well occur in real cases), Rüger's approximation did not perform satisfactorily for forward or inverse modelling. However, it appears that Rüger's approximation can always be used to obtain estimates of the azimuthal fracture orientation with small uncertainty, even when the contrast and anisotropy levels are extremely large. In order to illustrate the significance of our findings within the context of seismic fracture characterization, we analysed a set of synthetic seismic AVAZ data associated with a fault facies model where the fracture density decreases exponentially with distance from the fault core, and a set of real seismic AVAZ data involving offset-averaged (root mean square) maps for six azimuthal sectors. Our results suggest that the difference between the maps of inverted fracture densities (which partially determines the effective permeability) obtained using Rüger's approximation can be very different from those obtained using the exact reflection coefficients; but Rüger's approximation can still be used to obtain qualitative information about the trends in the spatial distribution of fractures.

Cabled observatory vent imaging sonar.

A cabled observatory vent imaging sonar (COVIS) has been developed to provide plume and Doppler imaging of hydrothermal vents and surrounding diffuse flow. The system was designed to be compatible with the power and data interface standards of the Neptune Canada cabled observatory. COVIS is a 4 m tall, titanium tripod employing a Reson 7125 multibeam sonar. The sonar transducers are positioned by a motor‐driven three degree of freedom rotation system (pitch, roll, and yaw). A 400 kHz, 1 × 128 deg fan‐beam projector is used with a receiver array that forms 256 beams having horizontal width 0.5 deg and covering a 128 deg azimuthal sector. Volumetric imaging of plumes is generated as the transducer array is scanned in 1 deg pitch steps. Doppler measurements of flow velocity over a 3‐D grid are also derived. A 200 kHz, 28 × 128° broad beam projector is used to image the diffuse areas near the base of the hydrothermal vent edifices. Software allows for the creation of complex, arbitrary, autonomously executed experiments that control all aspects of the sonar and rotation system. COVIS was successfully deployed in September 2010. The design of COVIS provides insights relevant to future cabled acoustic systems. [Work supported by NSF.]

Sampling gap fraction and size for estimating leaf area and clumping indices from hemispherical photographs

Hemispherical photography is becoming a popular technique for gap fraction measurements to characterize biophysical parameters and solar radiation in plant canopies. One of the crucial steps in the measurement of canopy gap fraction using hemispherical photography is determining the resolution of the sampling grid. In this work, the effects of varying resolutions of sampling grids by modifying the angle widths of zenithal annuli and azimuthal sectors were evaluated for leaf area and clumping indices computations. Sensitivity analysis was performed to test these effects using artificial photographs simulating ideal canopies with varying leaf area index and aggregation levels of foliage elements. Contrasting forest types, including natural tropical cloud forest and exotic plantations, were tested as real canopies. Results indicate that leaf area and clumping indices estimates are significantly affected by the variation of sampling grids. A new approach to solve the problem of null-gap segments, obscured completely by foliage, is proposed. However, the determination of optimal combinations of zenithal annuli and azimuthal sector angular widths that suit all canopy types remains a difficult practical problem that is often overlooked. Finally, theoretically sound gap fraction and size sampling regions were demonstrated for reliable estimates of canopy biophysical parameters.

Scour and three dimensional turbulent flow fields measured by ADV at a 90 ° horizontal forced bend in a rectangular channel

The three dimensional turbulent flow fields and scour at a 90° horizontal forced bend were investigated experimentally. Non-cohesive non-uniform sediments with median diameter d 50 equal to 0.3 mm were used. The flow depth and velocity in the upstream section were adjusted to get a shear velocity equal to 1.61 times the critical shear velocity of the bed particles. The time averaged velocity components, turbulent intensity components and Reynolds stresses on a stabilized scoured bed were taken by the Acoustic Doppler Velocimeter (ADV) at different azimuthal sections. The presentation of flow fields through vectors at the horizontal section mainly shows that there is a concentration of flow in the concave bank at the bend. It is found from the measured bed profile that the non-dimensional maximum scour depth (scour depth/width of channel) is approximately 0.17 at the bend under the above flow conditions. The maximum measured velocity was approximately 1.61 times the average velocity. The data obtained in the experimental investigation will be useful for the proper design of protection works at bends.

MAZ depth-velocity modelling and imaging with azimuthal anisotropy

Processing of multi and wide-azimuth seismic data faces some new challenges, and one of them is depth-velocity modelling and imaging with azimuthal velocity anisotropy. Analysis of multi-azimuth data very often reveals noticeable fluctuations in moveout between different acquisition directions. They can be caused by several factors: real azimuthal interval velocity anisotropy associated with quasi-vertical fractures or present day stress field within the sediments; short-wavelength velocity heterogeneities in the overburden; TTI (or VTI) anisotropy in the overburden; or, random distortions due to noise, multiples, irregularities in the acquisition geometry, etcetera. In order to build a velocity model for multi-azimuth pre-stack depth migration (MAZ PSDM) taking into account observed azimuthal anisotropy, we need to recognise, separate and estimate all the effects listed above during iterative depth-velocity modelling. Analysis of seismic data from a full azimuth 3D seismic land survey revealed the presence of strong spatially variable azimuthal velocity anisotropy that had to be taken into consideration. Using real data examples we discuss major steps in depth processing workflow that took such anisotropy into account: residual moveout estimation in azimuth sectors; separation of different effects causing apparent azimuthal anisotropy (see A–D above); iterative depth-velocity modelling with azimuthal anisotropy; and, subsequent MAZ anisotropic PSDM. The presented workflow solved problems with azimuthal anisotropy in our multi-azimuth dataset. Some of the lessons learned during this MAZ project are relevant to every standard narrow azimuth seismic survey recorded in complex geological settings.

Seismic imaging of thrust fault structures in Zagros Iranian oil fields, from surface and well data

The Aghajari field is located in the Dezful Embayment, one of major structural zone in Zagros fold-thrust belt containing most of Iranian oil fields. The late Oligocene-early Miocene Asmari formation is one of the main reservoir rocks of SW Iran with several decades of production history from different oil fields in the region. The objective of the present Ph-D thesis is to improve the structural understanding of the Aghajari field using 3D seismic imaging for the first time, and well seismic. the lack of seismic response of the dipping horizons in the reservoir oil zone constitutes a major identified difficulty. Given the dip values of 30° to 45° of the reflectors in the pay zone, the P-P reflections are expected to appear mainly on the horizontal components of the VSP data, justifying the processing of the 3 components (3C). An innovative method of 3C VSP orientation was developed. The 3C VSP results confirm the presence of dipping reflectors, with dip values in agreement with surface seismic, on the eastern flank of the structure. Several new approaches of seismic imaging have been applied in order to investigate and improve the reservoir illumination. The “Beyond Dix” workflow of CGGVERITAS was applied to land seismic data for the first time; this process enables to build a depth/velocity model from the dips read on the PSTM image (pre-stack time migration), and the residual move out corrections. The depth migrated image is improved in the overburden, unfortunately not at reservoir level, due to low signal to noise, interference with multiples, thus poor dip and velocity determination in the reservoir interval. A new Kirchhoff PSTM prototype technique was developed in IFP, allowing a selection of azimuth sector, offset range and geological dip, with automatic optimization of the local dip. The results from this new technique show clear improvements in dip determination and signal to noise ratio of the migrated image. The additional study of another exploration anticline in Zagros, using surface seismic, well data, VSP and geological information illustrates how an integrated data analysis can improve the understanding of deep structures, and therefore help making more reliable drilling decisions, if achieved timely. In Zagros, Surface seismic is definitely a good tool for the structural exploration, but its application to fine reservoir studies has not been demonstrated, in spite of the efforts achieved in the present study.

Alignment of the ATLAS muon spectrometer with tracks

The muon spectrometer of the ATLAS experiment at the Large Hadron Collider is designed to measure the muon momenta of up to 1 TeV/ c with a resolution of better than 10% in a toroidal magnetic field of superconducting air–core magnets. The muon track sagitta is measured in three layers of pressurized drift-tube chambers. The precision muon chambers have to be aligned with an accuracy of better than 30 μ m in the track bending plane. An optical alignment system monitors movements of the muon chambers with a precision of few microns. In order to determine the chamber positions in the spectrometer, the initial chamber positions have to be measured with 30 μ m accuracy using straight muon tracks from proton–proton collisions in a dedicated run of the ATLAS detector with the toroid magnets turned off. A Least Square algorithm has been developed which determines the misalignment parameters of a complete azimuthal sector of the barrel part of the muon spectrometer. It has been tested with straight cosmic muon tracks during the commissioning of the ATLAS experiment. Simulations show that the required alignment accuracy is reached with 100,000 muons per sector originating from the interaction point with transverse momentum greater than 10 GeV. About half of the barrel chambers have already been aligned with 30 μ m accuracy using cosmic muons.

Planar C-Band Antenna with Electronically Controllable Switched Beams

The design, manufacturing, and measurements of a switchable-beam antenna at 3.5 GHz for WLL or Wimax base station antennas in planar technology are presented. This antenna performs a discrete beam scan of a60∘sector in azimuth and can be easily upgraded to 5 or more steps. The switching capabilities have been implemented by the inclusion of phase shifters based on PIN diodes in the feed network following a strategy that allows the reduction of the number of switches compared to a classic design. The measurements show that the design objectives have been achieved and encourage the application of the acquired experience in antennas for space applications, such as X-band SAR and Ku-band DBS.

Converted-wave splitting estimation and compensation

Converted-wave (C-wave) splitting estimation and compensation (SEAC) estimates and removes the effects of shear-wave splitting from C-wave data. A locally 1D earth is assumed where a priori rotation of the field data to radial-transverse coordinates is valid. Subsurface fractures (horizontal transverse isotropy [HTI] layers are assumed) polarize C-wave reflection energy onto the transverse component, and introduce azimuth-dependent traveltime variations to the radial component. SEAC estimates the fast principal direction of the fractures, and the amount of traveltime splitting, from input radial and transverse azimuth-sectored stacks. SEAC also produces a splitting-compensated radial component, and a data misfit transverse component. Local fracture variations not accounted for in the coarse-interval inversion may be interpreted in the data misfit. Synthetic data generated by anisotropic reflectivity modeling for a model containing two HTI layers having different principal directions was used to illustrate SEAC. The field data example used was from a large3-C, 3D Vectorseis survey from onshore China. Preprocessed C-wave data (radial and transverse components) were prestack time migrated into offset planes within 10-degree azimuth sectors. These data were then corrected for residual moveout (azimuth-independent correction), and stacked over offset to produce azimuth-sectored stack gathers that were input to SEAC. SEAC estimated the azimuth of the fast principal direction [Formula: see text] and the amount of traveltime splitting [Formula: see text] that describe the overburden anisotropy. Spatially variable parameter estimates for the entire 3D data set, ([Formula: see text] and [Formula: see text]), produce significantly reduced energy on the transverse component at all record times after inversion. Azimuth-dependent traveltime variations on the input radial data were also significantly reduced at all record times, resulting in a postinversion radial full-azimuth stack having improved reflection continuity and temporal bandwidth. The data misfit (transverse component after inversion) potentially revealed local variations in shear-wave splitting not accounted for by the overburden layer-stripping correction.

The behaviour of Couette-Taylor flow in an azimuthal plane

We investigated the behaviour of Couette-Taylor flow in an azimuthal cross section by flow visualization using Kalliroscope flakes, and by image analysis of the obtained movie. Kalliroscope flakes are platelet and can make shear flow visible. Wavy vortex flow mode (WVF) in which an azimuthal wave mode superposes Taylor vortex flow mode (TVF) was investigated. Wave number and phase velocity of the azimuthal wave appearing in WVF at higher Reynolds number were determined by image analysis. Azimuthal flow structure of modulated wavy vortex flow mode (MWVF) was clearly visualized and the modulation component of MWVF was investigated by Fourier analysis of a temporal variation of brightness distribution extracted from a movie of visualized flow. Continuous wavelet analysis shows that spatial-temporal behaviour of MWVF on an azimuthal plane: the modulation first appears near the outer cylinder and spreads globally.

Demonstration of a Shaped Beam Reflectarray Using Aperture-Coupled Delay Lines for LMDS Central Station Antenna

A shaped-beam reflectarray based on patches, aperture-coupled to delay lines is demonstrated for local multipoint distribution system (LMDS) central station antennas, in the 10.10-10.70 GHz band. The antenna must cover a 60 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">deg</sup> -sector in azimuth with a squared cosecant pattern in elevation. The design process consists of two steps. First, a phase-only pattern synthesis technique is applied to obtain the required phase-shift distribution on the reflectarray surface which generates the shaped pattern. The second stage consists of determining the length of the delay lines, aperture-coupled to the square patches, in order to achieve the phase distribution synthesized in the previous step. Two reflectarray antennas have been designed, one for vertical (V) and the other for horizontal (H) polarization. A breadboard for V-polarization has been manufactured and tested in an anechoic chamber, showing a good agreement between theoretical and measured radiation patterns.

Secondary phase validation—Phase classification by polarization

A long-standing problem in operational seismology is that of reliable focal depth estimation. Standard analyst practice is to pick and identify a ‘phase’ in the P-coda. This picking will always produce a depth estimate but without any validation it cannot be trusted. In this article we ‘hunt’ for standard depth phases like pP, sP and/or PmP but unlike the analyst we use Bayes statistics for classifying the probability that polarization characteristics of pickings belong to one of the mentioned depth phases given preliminary epicenter information. In this regard we describe a general-purpose PC implementation of the Bayesian methodology that can deal with complex nonlinear models in a flexible way. The models are represented by a data-flow diagram that may be manipulated by the analyst through a graphical-programming environment. An analytic signal representation is used with the imaginary part being the Hilbert transform of the signal itself. The pickings are in terms of a plot of posterior probabilities as a function of time for pP, Sp or PmP being within the presumed azimuth and incident angle sectors for given preliminary epicenter locations. We have tested this novel focal depth estimation procedure on explosion and earthquake recordings from Cossack Ranger II stations in Karelia, NW Russia, and with encouraging results. For example, pickings deviating more than 5° off ‘true’ azimuth are rejected while Pn-incident angle estimate exhibit considerable scatter. A comprehensive test of our approach is not quite easy as recordings from so-called Ground Truth events are elusive.