J.T. Fokkema

Delft University of Technology | TU · Department of Imaging Science and Technology

In the seventies, scientists observed discrepancies of the bending of light around the Sun based on Einstein's prediction of the curvature of star light due to the mass of the Sun. Discussions have become silent, because no rigorous theoretical model was proposed. We claim that the interior electromagnetic properties of the Sun influence the curvat...

Electromagnetic logging is a technique used to probe differences in electric conductivity around a measurement device. Electromagnetic logging while drilling can contribute to proactive geosteering to improve well placement in reservoirs because such measurements can serve as an indication for the structure of the surrounding geology. We have devel...

Seismic data recorded in a marine streamer are obtained, sorted as a common receiver gather. A complex Laplace frequency parameter is used to transform the seismic data from a space-time domain to a spectral domain. An iterative conjugate gradient scheme, using a physically-based preconditioner, is applied to the transformed seismic data, to provid...

Induction logging is used in hydrocarbon drilling operations to probe the local subsurface around a drilling bit. The scattered electromagnetic field at the tool receivers depends directly on the conductivity of its surroundings. These differences in conductivity can serve as a proxy to discriminate between oil- and water baring layers. The computa...

A method is disclosed for deghosting and water surface multiple reflection attenuation in marine seismic data. The method includes decomposing data acquired at two water depths with sensors that measure the same parameter into upgoing and downgoing wavefield components. The decomposing includes, in one embodiment, transforming the data into the spa...

marine seismic acquisition, the free surface generates seismic events in our recorded data that are often categorized as noise because these events do not contain independent information about the subsurface geology. Ghost events are considered as such noise because these events are generated when the energy generated by the seismic source, as well...

Seismic data recorded in a marine streamer are obtained, with the seismic data being representative of characteristics of subsurface earth formations and acquired by deployment of a plurality of seismic receivers overlying an area of the subsurface earth formations to be evaluated, the seismic receivers generating at least one of an electrical and...

For the computational solution of the acoustic scattering problem, new domain integral equations are proposed. These domain integral equations describe the acoustic wave propagation in some chosen inhomogeneous background, whereas the influence of the scattering object is viewed as a superposition of contrast sources. A stretching procedure of the...

Maurice Ewing Medal for Anthony R. Barringer Maurice Ewing Medal for M. Nafi Toksöz Honorary Membership for Michael S. Bahorich Honorary Membership for Walter S. Lynn Honorary Membership for Bjørn Ursin Virgil Kauffman Gold Medal to Gerard Thomas Schuster Virgil Kauffman Gold Medal to Kees Wapenaar Reginald Fessenden Award to Samuel Gray Reginald F...

The simulation of migrated and inverted data is hampered by the high computational cost of generating 3D synthetic data, fol-lowed by processes of migration and inversion. For example, simulating the migrated seismic signature of subtle stratigraphic traps demands the expensive exercise of 3D forward modeling, followed by 3D migration of the synthe...

We formulate the theory for a direct nonlinear seismic inversion method in the acoustic approximation. It is a completely data-driven method, aiming at the determination of subsurface properties directly from the data. The theory is presented for the full three-dimensional, laterally varying case. For this situation we derive a layer replacement me...

Wavefield-extrapolation (WE) implementations of the one-way scalar wave equation are relatively simple to write, compared with a Kirchhoff scheme, but in principle, they are costlier. The extra cost can be prohibitive if many iterations are needed for constructing the velocity model. With Kirchhoff migration, it is routine to output the data sorted...

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We present fast and efficient plane-wave migration methods for densely sampled seismic data in both the source and receiver domains. The methods are based on slant stacking over both shot and receiver positions (or offsets) for all the recorded data. If the data-acquisition geometry permits, both inline and crossline source and receiver positions c...

The term seismic interferometry refers to the principle of generating new seismic responses by crosscorrelating seismic observations at different receiver locations. The first version of this principle was derived by Claerbout (1968), who showed that the reflection response of a horizontally layered medium can be synthesized from the autocorrelatio...

Seismic reflection data always exhibit a progressive loss of high-frequency energy with time. This effect is partly attributable to irreversible processes such as the conversion of elastic energy into heat (commonly known as absorption), and partly to reversible processes associated with interference between reflected waves arriving at different ti...

Ground coupling are terms that describe the transfer from seismic ground motion to the motion of a geophone. In previous models, ground coupling was mainly considered as a disk lying on top of a half-space, not considering the fact that in current practice geophones are spiked and are buried for optimal response. In this paper we introduce a new mo...

We compare two approaches for deriving the fact that the Green's function in an arbitrary inhomogeneous open system can be obtained by cross correlating recordings of the wave field at two positions. One approach is based on physical arguments, exploiting the principle of time-reversal invariance of the acoustic wave equation. The other approach is...

Constructing an image of the Earth subsurface from acoustic wave reflections has previously been described as a recursive downward redatuming of sources and receivers. Most of the methods that have been presented involve reflectivity and propagators associated with one-way wavefield components. In this paper, we consider the reflectivity relation b...

Purpose – To present the challenge of sustainable development, the way in which technology can address that challenge and the task of engineering education to train engineers for it. Design/methodology/approach – The paper describes briefly the history of the environmental and sustainability discourse in The Netherlands, as a densely populated co...

Stress is the most important parameter to understand basin dynamics and the evolution of hydrocarbon systems. The state of stress can be quantified by numerical geo-mechanical modelling techniques. These techniques require static elastic parameters of the rocks as input, while tectonic and gravitational forces are given as explicit boundary conditi...

In geophysical exploration different types of measurements are used to probe the same subsurface region. In this paper we show that the wavelet transform can aid the process of linking different data types. The continuous wavelet transform, and in particular the analysis of amplitudes along wavelet transform modulus maxima lines, is a powerful tool...

1] The interaction of elastodynamic waves with imperfect interfaces is usually described by the so-called linear slip model. In this model it is assumed that the particle displacement of an elastic wave at an interface jumps by a finite amount, linearly proportional to the stress at the interface. In this paper we postulate general boundary conditi...

Understanding the nature of the ground-penetrating radar (GPR) reflection response in terms of the dielectric permittivity and conductivity contrast is an important factor in interpretation. This is the reason for the present study, which aims to carry out an experiment in a controlled fashion, so that the relationship between measurements and the...

Diffusion, flow, and wave phenomena can each be captured by a unified differential equation in matrix-vector form. This equation forms the basis for the derivation of unified reciprocity theorems for diffusion, flow and wave phenomena.

Geomechanical modeling techniques require static elastic parameters of the rocks as input, while tectonic and gravitational forces are modeled as boundary conditions to compute the local state of stress at different scales. We developed a technique to determine the density and elastic constants at seismic frequencies using full Zoeppritz inversion...

Love waves are one of the major contributors of noise in SH-wave reflection data. Suppressing them can be difficult, most importantly because their group velocity is almost equal to the shear wave velocity. By using the Betti-Rayleigh reciprocity theorem for elastic media, modified for SH waves only, we derive an integral equation of the second kin...

We compare two geophysical survey measurements of the same type made at different times in order to characterize the change in the geological medium during the elapsed time. The aim of this study is to develop a strategy using a full non-linear inversion algorithm as the interpretation tool. In this way, not only the location and the form of the ch...

Scalar imaging algorithms originally developed for the processing of remote sensing measurements (e.g., the synthetic-aperture radar method) or seismic reflection data (e.g., the Gazdag phase-shift method) are commonly used for the processing of ground-penetrating radar (GPR) data. Unfortunately; these algorithms do not account for the radiation ch...

Understanding the nature of the georadar reflection response in terms of the dielectric permittivity and conductivity contrast is important in the realm of interpretation. This motivates the present study, which has the aim to carry out an experiment in a controlled fashion such that the relation can be established between the measurement and the r...

Seismic reflection response can be used to resolve the processes involved in the sedimentary basin developments. In this study we are trying to find to what extent this can be achieved. Integration of geomechanical modelling and seismic data analysis is required to answer this question. Geomechanical modelling is a multi-purpose study and one of th...

In this paper we discuss a new type of regularization technique for the nonlinear inverse scattering problem, namely the multiplicative technique. The main advantage is that we do not have to determine the regularization parameter before the inversion process is started. We consider different norms of the total variation as regularization factor. S...

This paper deals with the scattered field data measured by a closed microwave scanner and discusses the removal of the effects of the metal casing as a preprocessing step before actual inversion of the data can take place. It is shown that Rayleigh's reciprocity theorem furnishes a relation between the scattered field data obtained in the closed mi...

To improve image resolution of GPR data, proper data acquisition is the first key part of the whole imaging sequence. Obtainable down and cross range resolutions, insofar as they are related to acquisition, are determined by the frequency bandwidth of the GPR equipment, the temporal and spatial sampling rates and the accurate knowledge of the anten...

One-way wave equations play a fundamental role in the formulation of imaging schemes for reflection measurements, as in seismic exploration and ground-penetrating radar. In this paper we review the theory for electromagnetic one-way wave fields, including dissipation, and we derive reciprocity theorems for these one-way wave fields. First we consid...

We discuss a time-lapse technique using a full nonlinear inversion scheme for subsurface monitoring purposes. In this technique we relate two measurements of the same nature but at different time instants to characterize the change of the subsurface during this time of evolution. This technique is very popular in seismic geophysical explorations. I...

The main objective of our work is to explore the feasibility of designing an airborne RADAR system much like the University of Texas Institute for Geophysics airborne ice-penetrating radar systems for use in the detection of underground structures. Here we summarize our initial efforts toward achieving this goal. The studies conducted so far includ...

For electromagnetic imaging the vectorial character of the emitted field and the radiation characteristics of both source and receiver play an important role. Recently, a new imaging algorithm was presented dedicated to the electromagnetic case. The radiation characteristics of GPR source and receiver antennas and the vectorial nature of the electr...

Continental topography is at the interface of processes taking place at depth in the Earth, at its surface, and above it. Topography influences society, not only in terms of slow processes of landscape change and earthquakes, but also in terms of how it affects climate. The Pannonian Basin-Carpathian Orogen System in Central and Eastern Europe repr...

In this paper we present the simulation and design of a directional borehole radar. In addition we discuss an imaging method for the radar system. The antenna system contains an electric dipole which is in one direction shielded by a cylindrical perfectly conducting reflector. The radiation pattern of the reflected wavefield is computed by first so...

Numerical modeling of thin-wire antennas is interesting to people working on antenna design and to people working on the processing and interpretation of radar data. They have different demands regarding the output of the model code. Our primary interest lies with improving image resolution through processing of ground-penetrating radar data. For t...

Electric dipoles radiate an electromagnetic field into their surroundings. The electric and magnetic fields from a point source or from linear dipoles have components parallel to a spherical surface but also a radial component. In most investigations on radiated fields, only the part of the electric field that is parallel to a spherical surface is...

A borehole radar with directional radiation pattern that fits in a single borehole was designed and developed. The radiation pattern of the antenna system was computed to obtain a 3D image of the subsurface. The best resolution in the radial direction using back-propagation was obtained for the measured data. It was found that the amplitudes corres...

This paper deals with the problem of localizing and characterizing cylindrical dielectric objects embedded in a homogeneous half-space from the knowledge of the electromagnetic scattered fields, i.e., the measurement data. We present and compare linear and nonlinear inversion algorithms based on the contrast source formulation. Both inversions are...

We describe a directional borehole radar system. The antennas are positioned in a bi-static set-up. In order to obtain a focused radiation pattern, the transmitting and receiving dipoles are shielded with a curved reflector. The radiation pattern of this scattered wavefield is computed by solving the integral equation for the unknown elec- tric sur...

Departuut oÍ Applied Earth kiences, Delí1 Universit! oÍ Tecluolog!, P.O. Bot 5028, 26N GA, DelÍt, The Nethc an^ Prese Address: Deparinent oÍ Seismologf, InsdrÉ dc PlEsíquc dtt Globe, 4 Phce Jussíeu, 75m5 Paás, France. ABSTRACT Mercerat, E.D., Wapenaar, C,P.A., Fokkema, J.T. and Dillen, M., 2002. Scaling behaviour of the acoustic transmission respon...

A boundary integral representation of the difference of two time-lapse acoustic wave fields is investigated. Recursive computation of the boundary integral eliminates the action of temporal contrast sources above the boundary at which the integral is evaluated. This method is a basis for pre-stack temporal contrast imaging and inversion schemes, an...

We formulate reciprocity theorems for time-lapse seismic methods, based on the full and the one-way wave equations. The latter form allows a straightforward physical interpretation of the various contributing terms. Unlike difference data taken at the acquisition surface, the boundary integral in the one-way reciprocity theorem represents the true...

In this paper we describe a directional borehole radar system. We first present the simulation and design of the antenna system. The antennas are positioned in a bistatic setup. In order to obtain a focused radiation pattern the transmitting and receiving dipoles are each shielded with a curved reflector. The radiation pattern of this scattered wav...

In this paper the nonlinear iterative algorithm, the so-called Extended Contrast Source Inversion is applied to subsurface sensing problem where the number of measured data are very limited and the unknown objects/layers are illuminated from only one side. Some numerical results obtained from synthetic and real data are presented to illustrate the...

Reciprocity theorems have proven their usefulness in the study of forward and inverse scattering problems. Most reciprocity theorems in the literature apply to the total wave field and are thus not compatible with one-way wave theory, which is often applied in situations in which there is a clear preferred direction of propagation, like in electrom...

Ultrasonic experiments carried out on several reservoir sandstone samples have shown a specific pressure- dependent behaviour of the transmission response. Apart from the well-known velocity increase as ambient pressure increases, the amplitude and the time axis are scaled as a function of the pressure. In order to quantify the scaling phenomenon t...

We present the simulation and design of an antenna system for a borehole radar. To obtain a directional radiation pattern the transmitting dipole is shielded with a reflector. The generated transient wavefield, with a centre frequency of 100 MHz, is reflected in the desired direction by a perfectly conducting cylindrically curved plate. The radiati...

Summary Seismic attribute analysis has gone through a major revolution due to the introduction of three-dimensional seismic imagery. Features of special interest are the local geometry of the seismic signal and its frequency content. We have developed a new kind of wavelet transform that has the ability to both separate approxi- mately the angular...

Apparent resistivity is a useful concept for initial quickscan interpretation and quality checks in the field, because it represents the resistivity properties of the subsurface better than the raw data. For frequency-domain soundings several apparent-resistivity definitions exist. One definition uses an asymptote for the field of a magnetic dipole...

The aim of an imaging procedure is to transform measured reflections to their true reflection position, by compensating for the propagation effects, resulting in a representation of the contrasting domain as accurate as possible. Several 3D imaging algorithms for Ground Penetrating Radar (GPR) data exist.

Due to the low velocity of shear waves, SH-wave (Shear Horizontal) reflection seismics provide a promising tool for imaging the shallow subsurface. However, SH-wave shot records often contain shot-generated noise, of which the largest contribution is due to Love waves, which are a kind of surface waves. Several characteristics of Love waves make it...

In this paper we review our reciprocity theorems for one-way wave fields, modified for lossy media, and we discuss applications in multiple elimination and time-lapse seismics.One-way wave equations have played a prominent role in seismic processing since the pioneering work of Claerbout [4], Berkhout [2] and others. The reason for this is that a s...

By calculating a convolution type integral involving two time-lapse wave fields, at a certain depth, one obtains a representation, which is equivalent to a difference wave field at the recording level. This difference wave field shows no difference reflections from temporal contrasts above the interaction depth. If the wave fields, appearing in the...

Three-dimensional imaging of ground penetrating radar data is a challenging task. Most imaging procedures are based on scalar seismic imaging algorithms. However, for electro- magnetic imaging the vectorial character of the emitted field and the radiation characteristics of the source and the receiver play an important role. In this paper a new ima...

Ultrasonic experiments on a dry Colton sandstone placed in a triaxial pressure machine show that effective stress changes lead to distinct anisotropic velocity changes in compressional waves and shear waves. The stress imprint can be recognized from the associated velocity pattern by relating the velocities to the three normal stress directions. Th...

Split-step Fourier migration method was #rst developed and aplied to migrate zero-o#set seismic data by Sto#a et al. #1990#. This method is an extension of Gazdag's phase-shift migration that accommodates lateral velocityvariations. It is based on decomposing the laterally varying slowness function into two components; a mean slowness component an...

In this paper the coupling of a sensor to an acoustic medium is discussed. Based on the acoustic reciprocity theorem, an expression is derived for the motion of the sensor as a function of the undisturbed motion of the embedding medium. What is special here is that the sensor is the scattering object. The sensor coupling is affected by two factors:...

IntroductionAs stated by Dake (1978) the overburden pressure in a reservoircan be equated to the sum of the fluid pressure and thegrain or effective pressure. From this it follows that a decreaseof fluid pressure during production can be directly related toan increase of formation pressure. In our experimental studywe relate stress, in the 0-82 MPa...

Summary Most approaches to inverse wavefield extrapolation have in com- mon that the operator is defined as the time-reversed (or com- plex conjugated) forward operator. Despite the time-symmetry of the wave equation, this time-reversal introduces errors even for the simple situation of a homogeneous medium and an infi- nite aperture. In strongly i...

A fast and efficient optimization procedure is presented to meet the minimum-energy criterion for the determination of the source wavelet in the process of elimination of surface-related wavefield phenomena. The energy criterion is formulated in the frequency domain and a minimization over all frequencies and traces is taken as point of departure....