Fast Estimation of Parameters of a Layered-dipping Earth Model by Inverting Reflected Waves

Xia, Jianghai; Miller, Richard D.

doi:10.4133/jeeg5.2.21

Cited by 4 publications

(2 citation statements)

References 17 publications

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“…2). This model is common in mapping bedrock and any significant alluvial/colluvial acoustic contrasts between the bedrock and the ground surface in shallow reflection survey (e.g., Miller et al 1995;Xia & Miller 2000). An inverted velocity model by travel time inversion of real data acquired in Lake Tahoe, California, showed that velocities change from 1000 m/s to 1800 m/s in the top 200 m of the Earth (Xia & Miller 2000).…”

Section: Velocity Analysis Of a Synthetic Multi-flat-subsurface Modelmentioning

confidence: 99%

Accurate elevation and normal moveout corrections of seismic reflection data on rugged topography

Liu

Xia²,

Chen

et al. 2005

New Zealand Journal of Geology and Geophysics

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The application of the seismic reflection method is often limited in areas of complex terrain. The problem is the incorrect correction of time shifts caused by topography. To apply normal moveout (NMO) correction to reflection data correctly, static corrections are necessary to be applied in advance for the compensation of the time distortions of topography and the time delays from near-surface weathered layers. For environment and engineering investigation, weathered layers are our targets, so that the static correction mainly serves the adjustment of time shifts due to an undulating surface. In practice, seismic reflected raypaths are assumed to be almost vertical through the near-surface layers because they have much lower velocities than layers below. This assumption is acceptable in most cases since it results in little residual error for small elevation changes and small offsets in reflection events. Although static algorithms based on choosing a floating datum related to common midpoint gathers or residual surface-consistent functions are available and effective, errors caused by the assumption of vertical raypaths often generate pseudo-indications of structures. This paper presents the comparison of applying corrections based on the vertical raypaths and bias (non-vertical) raypaths. It also provides an approach of combining elevation and NMO corrections. The advantages of the approach are demonstrated by synthetic and real-world examples of multi-coverage seismic reflection surveys on rough topography.

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Section: Velocity Analysis Of a Synthetic Multi-flat-subsurface Modelmentioning

confidence: 99%

Accurate elevation and normal moveout corrections of seismic reflection data on rugged topography

Liu

Xia²,

Chen

et al. 2005

New Zealand Journal of Geology and Geophysics

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“…After each iteration the model is appropriately modified and the process continues until convergence, that is when further model updates do not affect the mismatch error E(x) (difference between the observed and calculated data). Deterministic methods were employed to provide stable solutions to inverse problems such as surface wave dispersion-curves inversion to find S-wave velocities (XIA et al, 1999(XIA et al, , 2003 and surface wave attenuation-curve inversion to find quality factors of near-surface materials (XIA et al, 2002) and to improve stability of inverse processing to an inverse problem of reflection travel time (XIA and MILLER, 2000). Convergence occurs when the inversion iterative process reaches a mismatcherror minimum.…”

Section: Introductionmentioning

confidence: 99%

The Inverse Problem of Refraction Travel Times, Part I:Types of Geophysical Nonuniqueness Through Minimization

Ivanov

Miller

Xia

et al. 2005

Pure appl. geophys.

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In a set of two papers we study the inverse problem of refraction travel times. The purpose of this work is to use the study as a basis for development of more sophisticated methods for finding more reliable solutions to the inverse problem of refraction travel times, which is known to be nonunique. The first paper, ''Types of Geophysical Nonuniqueness through Minimization,'' emphasizes the existence of different forms of nonuniqueness in the realm of inverse geophysical problems. Each type of nonuniqueness requires a different type and amount of a priori information to acquire a reliable solution. Based on such coupling, a nonuniqueness classification is designed. Therefore, since most inverse geophysical problems are nonunique, each inverse problem must be studied to define what type of nonuniqueness it belongs to and thus determine what type of a priori information is necessary to find a realistic solution. The second paper, ''Quantifying Refraction Nonuniqueness Using a Three-layer Model,'' serves as an example of such an approach. However, its main purpose is to provide a better understanding of the inverse refraction problem by studying the type of nonuniqueness it possesses. An approach for obtaining a realistic solution to the inverse refraction problem is planned to be offered in a third paper that is in preparation.The main goal of this paper is to redefine the existing generalized notion of nonuniqueness and a priori information by offering a classified, discriminate structure. Nonuniqueness is often encountered when trying to solve inverse problems. However, possible nonuniqueness diversity is typically neglected and nonuniqueness is regarded as a whole, as an unpleasant ''black box'' and is approached in the same manner by applying smoothing constraints, damping constraints with respect to the solution increment and, rarely, damping constraints with respect to some sparse reference information about the true parameters. In practice, when solving geophysical problems different types of nonuniqueness exist, and thus there are different ways to solve the problems. Nonuniqueness is usually regarded as due to data error, assuming the true geology is acceptably approximated by simple mathematical models. Compounding the nonlinear problems, geophysical applications routinely exhibit exact-data nonuniqueness even for models with very few parameters adding to the nonuniqueness due to data error. While nonuniqueness variations have been defined earlier, they have not been linked to specific use of a priori information necessary to resolve each case. Four types of nonuniqueness, typical for minimization problems are defined with the corresponding methods for inclusion of a priori information to find a realistic solution without resorting to a nondiscriminative approach. The above-developed stand-alone classification is expected to be helpful when solving any geophysical inverse problems.

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A moving hum filter to suppress rotor noise in high-resolution airborne magnetic data

et al. 2005

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A unique filtering approach is developed to eliminate helicopter rotor noise. It is designed to suppress harmonic noise from a rotor that varies slightly in amplitude, phase, and frequency and that contaminates aeromagnetic data. The filter provides a powerful harmonic noise-suppression tool for data acquired with modern large-dynamic-range recording systems. This three-step approach — polynomial fitting, bandpass filtering, and rotor-noise synthesis — significantly reduces rotor noise without altering the spectra of signals of interest. Two steps before hum filtering — polynomial fitting and bandpass filtering — are critical to accurately model the weak rotor noise. During rotor-noise synthesis, amplitude, phase, and frequency are determined. Data are processed segment by segment so that there is no limit on the length of data. The segment length changes dynamically along a line based on modeling results. Modeling the rotor noise is stable and efficient. Real-world data examples demonstrate that this method can suppress rotor noise by more than 95% when implemented in an aeromagnetic data-processing flow.

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Fast Estimation of Parameters of a Layered-dipping Earth Model by Inverting Reflected Waves

Cited by 4 publications

References 17 publications

Accurate elevation and normal moveout corrections of seismic reflection data on rugged topography

Accurate elevation and normal moveout corrections of seismic reflection data on rugged topography

The Inverse Problem of Refraction Travel Times, Part I:Types of Geophysical Nonuniqueness Through Minimization

A moving hum filter to suppress rotor noise in high-resolution airborne magnetic data

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