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26: Growth faults, offshore New Zealand. Younger sediments continue to be deposited in basins created as the fault blocks drop down to the left (courtesy of Don Lawton).
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The article presents the developing a model of adaptive state observer for single input-single output linear stationary discrete systems, based on non-recurrent algorithm for adaptive observation, using the least squares method. Examples, confirming the synthesized model workability will be presented to support the conclusions. Разработване на моде...
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... To confirm our polarity analysis, synthetic seismograms were computed using the CREWES finite difference algorithm (Margrave and Lamoureux, 2019) for two models of (1) a 10 m-thick lake underlying 760 m of glacial ice, and (2) a 20 m-thick consolidated sediment package underlying 760 m of glacial ice (Fig. 3b-c; Appendix A) and compared to the 200 acquired shot gather (Fig. 3a). The source wavelet used in the simulations was a negative minimum phase wavelet with dominant frequency 100 Hz, which best represents our impulse source (hammer and plate) and the direct wave observed in our seismic data. ...
In 2018 the first subglacial lake in the Canadian Artic was proposed to exist beneath Devon Ice cap, based on the analysis of airborne radar data. Here, we report a new interpretation of the subglacial material beneath Devon Ice Cap, supported by data acquired from multiple surface-based geophysical methods in 2022. The geophysical data recorded included 9 km of active source seismic reflection profiles, 7 transient electromagnetic soundings and 17 magnetotellurics stations. These surface-based geophysical datasets were collected above the inferred locations of the subglacial lakes and show no evidence for the presence of subglacial water. The acoustic impedance of the subglacial material, estimated from the seismic data, is 9.49 ± 1.92 x 106 kg m-2 s-1, comparable to consolidated or frozen sediment. The resistivity models obtained by inversion of both the transient electromagnetic and magnetotelluric measurements show the presence of highly resistive rock layers (1000 – 100000 Ω.m) directly beneath the ice. Re-evaluation of the airborne reflectivity data show that the radar attenuation rates were likely overestimated, leading to an overestimation of the basal reflectivity in the original radar studies. Here, we derive new radar attenuation rates using the temperature- and chemistry-dependent Arrhenius equation, and when applied to correct the returned bed power, the bed power does not meet the basal reflectivity threshold expected over subglacial water. Thus, the radar interpretation is now consistent with the seismic and electromagnetic observations of dry or frozen, non-conductive basal material.
... The wave refraction due to passing through the inhomogeneous medium is described by Snell's law [61]: ...
Paper ID: TRIG-D-22-00034
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During track construction or ballast bed maintenance, ballast layer compaction quality plays an essential role in the following track irregularities accumulation, its lifecycle, and maintenance costs. The ballast compaction process is characterized by its compaction and the accumulation of the stressed state. The elastic wave propagation methods are an effective way for the identification of the ballast bed compaction properties. The paper presents the theoretical and experimental studies of the ballast consolidation under the vibration loading of the sleeper. The practical laboratory study is given by the 1:2.5 scaled physical model of one sleeper and the corresponding ballast layer box. The measurements of ballast pressure and deformations under the vibration loading in the ballast layer and the photogrammetric recording of the ballast flow are carried out. The measurements demonstrate the accumulation of the residual stresses under the ballast layer. Furthermore, the measurements of elastic wave time of flight (ToF) using the shakers under the sleeper and acceleration sensors under the ballast show the substantial increase of the ToF velocities after the tamping process. Moreover, the distribution of the velocities along the sleeper is spatially inhomogeneous. The numeric simulation using the discrete element method (DEM) of the tamping and the testing processes proves the inhomogeneous wave propagation effect. The modeling shows that the main reason for the wave propagation inhomogeneity is the accumulated residual stress distribution and the minor one – the compaction density. Additionally, a method for identifying wave velocity spatial distribution is developed by wave tracing the inhomogeneous medium. The procedures allow ballast identification in the zones outside the shakers.
... Then, using the superposition principle, diffractions from multiple PDs were added to the 2D reflection traces. The modeling scheme is implemented in MATLAB using the CREWES toolbox 10.1029/2021EA002156 20 of 24 version 1,695 (Margrave, 2003) for the generation of the synthetic traces. In contrast to the 3D MADAGASCAR model, only horizontal reflectors were modeled using the same Baltic Sea velocity profile as for the 3D model (Tóth et al., 2014). ...
Small‐scale heterogeneities within the seafloor such as glacial boulders, concretions, or unexploded ordnance are of major scientific and economic interest. Because of their small size, such objects are hardly imageable by conventional seismic methods since they produce only faint diffractions. Despite the growing interest, reliable and efficient object detection methods are still not established. So, a marine acquisition system to image objects in the size range 0.3–4.1 m in the near‐surface has been designed and workflows have been developed. Source signals with a central frequency of ∼1,000 Hz are necessary to generate diffractions for the object size range. Performing beam pattern analyses, a rigid tow frame with the dimensions 8 × 3 m and attached hydrophones was designed. A synthetic aperture approach is realized to improve the resolution. Reflection events are suppressed in Normal‐Move‐Out corrected shot gathers by the muting of high singular values to enhance the diffractions. The diffractions are imaged with a beamforming algorithm with a high efficiency, as a total swath angle of about 80° in across‐track direction is covered. The processing of synthetic data sets allows an optimization and validation of the workflow and sensitivity analyses. Ground truthing is achieved with 1–2 m large boulders on the seafloor in 22 m depth, which were identified in a Multi‐Beam Echo Sounder data set. Although diffractions are only weak events in seismic data sets, 3D object detection with seismic beamforming has been found to be an efficient and reliable method to perform derisking for offshore infrastructure installations, drillings, or geologic interpretation.
... Under these circumstances, the ray path may bend, change direction, or re ect o surfaces, thus complicating analysis. [3]. Using the method of characteristics, we can transform this equation into a system of rst-order ordinary di erential equations (ODE) that can be solved by standard numerical methods where is slowness vector. ...
... Types and domains of tomography for velocity estimation[1] Full waveform inversion (also known as waveform tomography, wave equation tomography, and di raction tomography)The ray trajectories are found by solving a certain di erential equation that can be derived from the wave equation as follows[3]:Equation1 has a solution assumed in the form: where ( ⃗) and T( ⃗) are unknown functions describing amplitude and travel time that are expected to vary with position. Equation 4 is called the geometrical spreading equation because its solution can be shown to describe the ow of energy along a ray path. ...
Velocity model is essential for seismic data processing as it plays an important role in migration processes as well as time depth conversion. There are several techniques to reach that goal, among which tomographic inversion is an efficient one. As an upgrade version of handpicked velocity analysis, the tomography technique is based on the reflection ray tracing and conjugate gradient method to estimate an optimum velocity model and can create an initial high quality model for other intensive imaging and modelling module such as reverse-time migration (RTM) and full-waveform inversion (FWI). For the mentioned benefit, we develop a seismic travel-time reflection tomography (SeisT) module to study the accuracy of the approach along with building the technical capability in seismic processing. The accuracy of the module has been tested by both synthetic and real seismic field data; the efficiency and the accuracy of the model have been proven in terms of development method as well as field data application.
... 38 Since we can ignore some lowamplitude signals in thermoacoustic imaging, Stolt migration is a more efficient calculation method than phase-shift migration (PSM). 39 Equation (11) requires that the wave velocity is constant, and Stolt migration can, therefore, only be performed inside a single layer. Since the received wave field is limited by this transducer, we assume that the transmission factor at the interface is independent of the incident angle and only related to the dielectric impedance. ...
Microwave-induced thermoacoustic imaging (MTAI) is a potential nonionizing candidate for breast tumor detection due to its high contrast of tissue dielectric absorption and high resolution of ultrasonography. However, conventional MTAI systems need to contact the imaging targets through the ultrasound-coupling medium for the efficient transmission of thermoacoustic signals. This is a major drawback for potential applications such as navigation of open surgeries, burns, and ulcer testing. In this paper, we report a Fabry–Pérot (FP) interference principle-based non-contact thermoacoustic imaging system (NCTAIS). The system can infer the ultrasonic intensity by detecting the changes of the acoustically induced refractive index in the FP cavity. The miniaturized FP interferometer with a diameter of 5 mm achieves outstanding imaging sensitivity with a frequency response up to 1 MHz. An adaptive Stolt migration-based imaging reconstruction algorithm is proposed to solve the MTAI image distortion caused by the significant difference in sound velocity between air and a biological tissue. The NCTAIS is capable of achieving an axial resolution of 0.95 mm and a lateral resolution of 1.91 mm. The technical feasibility for breast tumor screening is validated with an in vitro simulated breast tumor model. The results demonstrate that the proposed NCTAIS offers high imaging sensitivity, high contrast, and deep imaging depth and will have more application scenarios than the conventional MTAI system, requiring the ultrasonic coupling medium to contact ultrasonic transducers.
... However, the number of (analytical) solutions of the wave equation is rare, and usually approximate numerical solutions are preferred for wave field modeling. Under this background, FDM has developed into a numerical technique in artificial seismic data calculation and has been widely used (Marfurt, 1984;Krebes and Lee, 1994;Manning and Margrave, 1998;Youzwishen and Margrave, 1999;Carcione et al., 2002;Margrave, 2003;Moczo et al., 2007). ...
Numerical modeling studies have a widespread application in exploration seismology in order to understand the seismic reflection responses of hydrocarbon traps formed in relation to tectonic structure, lithological changes and unconformities in complex geological environments and to develop effective data processing strategies. In this study, the seismic modeling of two important hydrocarbon trap models (Granite Wash and Normal Fault Trap) was performed by the Finite Difference Method (FDM), which provides the solution of the acoustic wave equation. Seismic data models were carried out in the pre-stack shot environment, and the obtained shot data were passed through appropriate data-processing stages to obtain stack and migration (zero offset) sections. By converting the obtained migration sections to depth, the spatial location and dimensions of hydrocarbon traps on the section were determined and it has been observed that they are compatible by comparing with the initial geological models. Thus, the seismic responses of hydrocarbon trap structures were learned, the importance of data processing was understood, and zero offset crosssections were obtained by processing of the generated synthetic shot records. Accordingly, it was observed that it is appropriate to make more and frequent shots in the investigation of granite wash type traps which are thin and short-width, whereas it is useful to make relatively less frequent shots in order to reduce the scattering intensity caused by the discontinuities of the fault type structures. Consequently, it is thought that before the field study for the hydrocarbon exploration, the modeling of the pre-stack shot instead of the post-stack modeling (zero offset) will contribute to the development of the data processing stages and the testing of the seismic section interpretation. In the future, such synthetic models and data processing will be developed for different complex trap structures and real data.
... This algorithm relies on the technique of Stolt migration of ultrasound waves back to its source in the domain 20 . Thealgorithm has been employed in various areas such as radar imaging, ultrasound, and seismic imaging applications [21][22][23] . However, frequency domain inversions have not been widely considered in optoacoustic imaging, outside of a few demonstrations with simulated and ex vivo data [16][17][18][19] . ...
Optoacoustic signals are typically reconstructed into images using inversion algorithms applied in the time-domain. However, time-domain reconstructions can be computationally intensive and therefore slow when large amounts of raw data are collected from an optoacoustic scan. Here we consider a fast weighted ω-κ (FWOK) algorithm operating in the frequency domain to accelerate the inversion in raster-scan optoacoustic mesoscopy (RSOM), while seamlessly incorporating impulse response correction with minimum computational burden. We investigate the FWOK performance with RSOM measurements from phantoms and mice in vivo and obtained 360-fold speed improvement over inversions based on the back-projection algorithm in the time-domain. This previously unexplored inversion of in vivo optoacoustic data with impulse response correction in frequency domain reconstructions points to a promising strategy of accelerating optoacoustic imaging computations, toward video-rate tomography.
... Second, wave models make it easier to draw the connection between NLOS imaging and related work in areas such as radar, seismic imaging, ultrasonic imaging, and other established fields. For example, it was recently shown how range migration techniques originally developed in the seismic imaging community [91,92], and later used synthetic aperture sonar (SAS) [93,94], ultrasound imaging [95], and synthetic aperture radar [96], result in some of the fastest and most robust NLOS imaging techniques [5]. It should be noted that the phase information of the light wave used in these experiments is not measured or required. ...
Emerging single-photon-sensitive sensors combined with advanced inverse methods to process picosecond-accurate time-stamped photon counts have given rise to unprecedented imaging capabilities. Rather than imaging photons that travel along direct paths from a source to an object and back to the detector, non-line-of-sight (NLOS) imaging approaches analyse photons {scattered from multiple surfaces that travel} along indirect light paths to estimate 3D images of scenes outside the direct line of sight of a camera, hidden by a wall or other obstacles. Here we review recent advances in the field of NLOS imaging, discussing how to see around corners and future prospects for the field.
... Esta solución se caracteriza por la construcción de rayos, que son construcciones geométricas perpendiculares al frente de onda y que indican la dirección de propagación de las ondas. En esta aproximación, la propagación del frente de ondas asociado a un conjunto de rayos está descrita por la ecuación Eikonal (Margrave, 2001). ...
En este trabajo se presenta una estrategia de trazado de rayos con aplicación a los problemas de tomografía sísmica. El trazador está basado en el método del camino más corto. La estrategia permite calcular trayectorias de rayos reflejados y refractados simultáneamente, generar rayos con varias fuentes y varios receptores, escoger puntos en interfaces de interés para generar reflexiones en dichos puntos, entre otras. Usando esta aproximación como estrategia de modelado, se implementó una tomografía de tiempos de propagación usando técnicas de reconstrucción algebraica, para estimar velocidades de propagación de ondas en el subsuelo. Se realizaron diferentes experimentos que muestran el comportamiento del trazador de rayos en diferentes escenarios con refracciones y reflexiones, así como los resultados del uso de la técnica de trazado de rayos en problemas de tomografía sísmica, obteniéndose resultados positivos en la identificación de estructuras en el modelo del subsuelo a un costo computacional relativamente bajo.
... The soft increase of the P-wave and S-wave velocities can be easier observed with the velocities profile (Fig1). With the parameters of the model it is possible to produce the ray tracing and extract the travel-time curves of the events PP and PS (Margrave, 2000 and2003;Thorbecke & Draganov, 2012), as it can be observed in Figure 2. ...
Many nonhyperbolic multiparametric travel-time approximations were developed in the last decades. As the seismic inversion became more popular, there were studies concerning the objective function of this kind of equations. Many of these approximations have a unimodal behavior where there is only the global minimum region while others have a multimodal statistical distribution with the global minimum region and one or more local minimum regions. However, two approximations showed both unimodal and multimodal behaviors to vary depending on the model. As the variation of the model generates only subtle distortions concerning the topology of the objective function, a method which can make this topology more abrupt is a solution to perform a more effective inversion. This kind of information can be reached using the L1-norm rather than the L2-norm, and with the comparison of the two norms for both reflection events (PP and PS) of the model and both approximations, it is possible to understand which kind of improvement it brings concerning the complexity and accuracy analysis.
