bluuebunny/crossref_metadata_2025_split huggingface dataset:
THE PHASE PROPERTY OF A FINITE REALIZATION OF RANDOM NOISE AND ITS INFLUENCE ON DECONVOLUTION *
Authors: DE VOOGD N. 
Published: April 2006

AbstractA finite realization of a discrete random noise process may be considered as a one‐sided energy signal. Its phase property can then be described by means of the center position. The samples of such a realization are the components of a random signal vector and the center position is therefore a random variable. A statistical analysis shows that the expected value of the center position equals half the time duration of the realization. This implies that the Z‐transform of the realization may be expected to have an equal number of poles and zeros inside and outside the unit circle. The standard deviation from the expected value of the center position is shown to depend on the time duration of the realization and on the autocorrelation of the process. It follows that, for processes that can be described by the convolution of a white series and a disturbance wavelet, the center position is independent of the phase property of the wavelet. A conclusion based on these results is that the homomorphic technique of wavelet estimation through cepstrum stacking must give questionable outcomes. Another conclusion is that the super‐position of a realization of random noise on a minimum phase wavelet will in general give a mixed phase resulting signal. It is pointed out that schemes for the derivation of deconvolution filters do not take account of this phenomenon.
THE THIN‐LAYER PROBLEM IN GEOELECTRICAL PROSPECTING *
Authors: MUNDRY E. 
Published: April 2006

AbstractFor a thin highly‐conducting layer with given longitudinal conductance the recurrence formulae for an n‐fold horizontally stratified subsoil are established for d.c. resistivity and magnetotelluric soundings. Similarly, a thin low conductivity layer with given transverse resistance is treated in the d.c. case and a non‐conducting intermediate bed in magnetotellurics. Model curves for a thin high‐ or low‐conductivity intermediate layer in the three‐layer case have been carried out, which may serve as an extension of the well‐known three‐layer diagrams for a Schlumberger configuration. The corresponding model curves in magnetotellurics are given.By numerical comparison of these curves with real three‐layer curves some diagrams have been developed to show the allowed thicknesses of the intermediate layer in the Schlumberger case and in the case of magnetotelluric sounding.
ESSAI D'UNE APPLICATION DE LA TRANSFORMATION DE KARHUNEN‐LOÈVE AU TRAITEMENT SISMIQUE *
Authors: HEMON CH. , MACE D. 
Published: April 2006

AbstractMultispectral recordings used for remote sensing are not without analogy with seismic records from CDP field set‐ups. These seismic data may be regarded as “photographs’ of deep regions of the earth taken from various angles.The Karhunen‐Loève (K.L.) transformation is commonly used for multispectral data processing, where it helps emphasize some features of remote sensing information. The same method may be applied to seismic data processing. Signal‐to‐noise ratio is improved on synthetic or field examples when K.L. transformation is applied instead of conventional CDP stacking. Residual statics seem to be diminished by a significant factor.
COMPUTATIONS OF SYNTHETIC SEISMOGRAMS FOR COAL SEAMS WITH THE REFLECTIVITY METHOD *
Authors: FERTIG J. , MÜLLER G. 
Published: April 2006

AbstractThe reflectivity method for computing synthetic seismograms can be applied to seismic prospecting problems with special focus on coal‐mining problems. The method allows the calculation of reflected waves for point‐source excitation and non‐vertical incidence. It automatically includes all possible conversions of wave types and all inner multiple reflections. Synthetic horizontal‐ and vertical‐component seismogram sections are given for a simple two‐seam model and for a realistic seam sequence which is represented by 48 layers; the source‐receiver distances range from 100 m to 1000 m. These seismograms show prominent PS reflections already at moderate source‐receiver distances. These waves complicate the vertical‐component records by producing arrivals of similar strength as the PP reflections. From this it is concluded that PS reflections in strongly layered media can cause problems in routine CDP stacking. On the horizontal‐component records the PS reflections are dominant. Because of the lower velocities of S waves the time resolution of PS reflections is better than that of PP reflections. This suggests that horizontal‐component recording may be useful in the investigation of subsurface regions with strong velocity contrasts, even with conventional energy sources producing mainly P waves.
STEEP DIP FINITE‐DIFFERENCE MIGRATION*
Authors: BERKHOUT A. J. 
Published: April 2006

AbstractA method is presented to derive approximate versions of the wave equation which allow finite‐difference migration for very steep dips (> 50°). It is shown that for conventional finite‐difference schemes, in addition to the dip limitation, the maximum acceptable frequency should be specified. A finite‐difference migration technique is proposed in the frequency domain. It is derived that finite‐difference wave field extrapolation in the frequency domain consists of a space‐variant convolution procedure for each frequency component, the space‐variance being defined by the lateral variation in the velocity.Finally it is shown that with finite‐difference migration, particle velocity data can be easily obtained from pressure data.
GEOPHYSICAL ANOMALY INTERPRETATION OF POTENTIAL FIELDS BY MEANS OF SINGULAR POINTS METHOD AND FILTERING*
Authors: CIANCIARA B. , MARCAK H. 
Published: April 2006

AbstractThe calculation of potential field anomalies on different levels below the measuring level permits to localize the singular points related to the sources of anomalies.It is possible to achieve considerable improvement of the resolution of this method

filtering of analytical downward continuation,
the use of the magnitude of the gravitational vector,
calculation of physe changes.

The numerical examples confirm these assumptions.
A SIMPLE APPROACH TO HIGH RESOLUTION SEISMIC PROFILING FOR COAL*
Authors: ZIOLKOWSKI A. , LERWILL W. E. 
Published: April 2006

AbstractSeismic exploration techniques which have been developed for oil prospecting contribute a valuable means for surveying coal measures. Since the object is to detect minor faults within the first 1500 m, rather than structural features at great depth, the new technique requires much higher resolution in the early part of the traditional seismic cross‐section.Higher resolution means broader bandwidth, which must be obtained by extending the high frequency end of the spectrum. This is achieved (a) by scaling down the explosive charge size and using single geophones instead of groups, and (b) by reducing the sampling interval in space and time. Noise which does not scale down includes static anomalies and ground‐roll. The consideration of statics, ground‐roll, and the high‐cut filtering effect of the near surface layers forces the use of deep shot holes and, where possible, deep detectors. This approach is confirmed by experiments and has been implemented on a regular basis in production.It is demonstrated that the present technique will clearly resolve faults with a vertical throw of about 5 m at 800 m depth.
CUBIC SPLINE APPROXIMATION OF INACCURATE RMS‐VELOCITY DATA*
Authors: WARD R. W. , REINING J. B. 
Published: April 2006

AbstractThe reliable determination of the root‐mean‐square seismic velocity from multiple coverage seismic reflection data requires coherent horizontal reflections equally spaced in time. Observational error in the rms‐velocity data produces significantly greater error in the instantaneous or interval velocity.A cubic spline approximation technique developed by Powell (1967) is designed to minimize the rapid velocity variation due to observational error and retain the significant variation in the rms‐velocity data. The approximation algorithm requires the difference between the observed and approximated rms‐velocity to be statistically random, and seeks to follow the “real” trends in the rms‐velocity measurements and reject observational error. Provided the trends of the rms‐velocity are reproduced, the instantaneous velocity derived from the spline approximation to rms‐velocity data with significant scatter is more reliable than the interval velocity determined from the inaccurate rms‐velocity values using the Dix (1955) approximation. This interval velocity is also a more reliable indicator of variations of lithology.The utility of the spline approximation of rms‐velocity is illustrated for a special common depth point (CDP) expanding reflection spread test recorded in Hardeman County, Texas by the Consortium for Continental Reflection Profiling (COCORP). In this wave test reflections are observed from several CDPs which are closely spaced. It is desired to combine the inaccurate observations from a collection of nearby CDPs. The approximation algorithm for the rms‐velocity determination is applied to both the rms‐velocity data for the individual CDPs and the collection of rms‐velocity data for eight nearby CDPs.
THE SUPPRESSION OF SURFACE MULTIPLES ON SEISMIC RECORDS*
Authors: KENNETT B. L. N. 
Published: April 2006

AbstractA new approach is presented for the suppression of multiples reflected at the surface of a horizontally layered fluid or elastic medium, recorded at non‐zero offsets from the source. The scheme used is to extract the effect of the free surface in the frequency‐wavenumber domain and then to replace this surface by a non‐reflecting boundary. The multiple suppression operator requires a detailed knowledge of the source time function and the elastic properties of the medium between the source and the surface.For a stratified fluid or a liquid layer overlying a stratified elastic medium, complete multiple suppression can be achieved with noise free data. If only the vertical component is available for an elastic medium an approximate approach may be used which removes most of the multiple energy. Good results may be achieved with this multiple suppression scheme in the presence of noise. The method is designed to be used before records are stacked in a CDP gather.
SOME RELATIONS BETWEEN POTENTIAL FIELDS AND THE STRENGTH AND CENTER OF THEIR SOURCES*
Authors: ANDERSEN F. H. , PEDERSEN L. B. 
Published: April 2006

AbstractFrom gravity it is well known how to determine the excess mass and the horizontal center of mass of the disturbing body. We show that a magnetic body—under rather weak assumptions—possesses excess magnetization and centers of magnetization (both horizontal and vertical), which can be uniquely determined from measurements. It also follows that the vertical center of mass can be uniquely determined from the vertical derivative of the gravity field.
MORE ON THE LATEROLOG* DEVICE**
Authors: MORAN J. H. , CHEMALI R. E. 
Published: April 2006

AbstractBasic Laterolog devices employ a measure‐current focusing technique to provide well logs of formation resistivity that feature sharp vertical definition combined with a depth of investigation much improved over those of normals of comparable spacings.To develop the concept of measure‐current focusing, a disk‐electrode arrangement analogous to a guard‐ring capacitor is considered first, leading finally to consideration of a real sonde in a cylindrical borehole. In the latter, auxiliary currents are adjusted to maintain substantially at zero the vertical potential gradients above and below the central measure‐current electrode; this has the effect of focusing the measure‐current beam.However, prediction of sonde responses on the basis of current patterns can in some cases be misleading. Indeed, for a given Laterolog array, one may use a (reciprocalmode) current pattern radically different from the one defined by the basic (direct‐mode) measure‐current focusing scheme and still obtain the same resistivity measurement. This feature is illustrated for Laterolog 3 by use of transfer impedances, and demonstrated for certain more general cases using the reciprocity theorem.Comparisons of Laterolog responses across typical thin beds, both non‐invaded and invaded, with those of normal devices of a comparable range of spacings illustrate the improved vertical resolution obtained with Laterolog devices. The examples also show the different magnitudes of the auxiliary currents (thenceforth designated “bucking”‐ or “focusing” currents) used in the direct and reciprocal modes and illustrate how these currents must continuously vary in order to maintain the focused condition as the sonde moves through the bed.Finally, briefly considering possible applications of Laterolog‐type arrays in surface prospecting, it is shown that a one‐dimensional array laid out on the surface does not provide the same degree of measure‐current focusing as is obtained in a borehole. Some improvement is obtained with a combination of two crossed linear arrays. Much more is obtained using a circular array.
SCALE MODEL ELECTROMAGNETIC RESPONSE TO INLINE AND BROADSIDE SYSTEMS AT SKEW TRAVERSES OF A DIPPING HALF PLANE EMBEDDED IN A CONDUCTING HOST ROCK*
Authors: GUPTA O.P. , JOSHI M.S. , NEGI J.G. 
Published: April 2006

AbstractLaboratory scale model experiments have been performed to obtain the electromagnetic response of a finitely conducting half plane embedded in resistive/conductive surrounding and excited by an oscillating magnetic dipole. Inphase and quadrature profiles are presented for two horizontal coplanar transmitter‐receiver systems (inline and broadside) for normal and skew traverses and for different dips of the conductor. It is observed that the broadside system is more diagnostic in delineating the strike and dip of the conductor and is more sensitive to the conducting host rock. The broadside profile over a vertical or dipping half plane is characterized, when traversing perpendicular to strike, by two positive peaks flanking a zero response when the coils are over the top edge of the conductor. For skew traverses a negative peak replaces the zero response. An increasing asymmetry in the anomalies is caused by changing the dip of the conductor from the vertical in both the systems, but it is more pronounced for the broadside system. The quadrature response in the broadside system changes in a characteristic way when the target is surrounded by a conducting host rock. The comparative results of the two systems may, therefore, be useful in the induction prospecting for ore deposits approximated by a half plane, especially in delineating the strike, dip, and effect of conductive host rock.
ON THE PROPERTIES OF THE RECIPROCAL GEOELECTRIC SECTION*
Authors: SEARA J.L. , CONAWAY J.G. 
Published: April 2006

AbstractThe interpretation of vertical electrical sounding data can be facilitated by the application of the reciprocal geoelectric section. If an apparent resistivity field curve has a descending right end, the apparent resistivity curve of the reciprocal geoelectric section can be obtained by the application of linear filter theory; from this the total transverse resistance of the geoelectric section can be calculated without having to interpret the field curve. In addition, Orellana's auxiliary point method can now be extended to interpret three and four layer apparent resistivity curves of all types.This paper summarizes the properties of the resistivity transform curve, the apparent resistivity curve, and the apparent resistivity curve of the reciprocal geoelectric section, with several new applications.
DIPOLE‐DIPOLE DEEP GEOELECTRIC SOUNDINGS OVER GEOLOGICAL STRUCTURES*
Authors: ALFANO L. 
Published: April 2006

AbstractAlfano L. 1980, Dipole‐Dipole Deep Geodectric Soundings over Geological Structures, Geophysical Prospecting 28, 283–296.The dipole‐dipole array is used for deep vertical geoelectric soundings for practical reasons. However, the data obtained are often too scattered and the quality is lower than that of a Schlumberger sounding. The mathematical transform from these fields data to the corresponding Schlumberger ones is needed. It is demonstrated that for more general underground structures different from plane parallel stratifications, only the continuous polar dipole‐dipole array permits a general and reliable transform of this type. It follows that any other dipole‐dipole array, (for instance the azimuthal, equatorial, parallel, perpendicular, etc.), are useless over complex structures, or in the presence of irregularities on the ground surface.
MAPPING NON‐REFLECTING VELOCITY INTERFACES BY NORMAL MOVEOUT VELOCITIES OF UNDERLYING HORIZONS*
Authors: KREY TH. 
Published: April 2006

AbstractThe normal moveout velocity of a reflecting bed is a function of the dips and curvatures of all overlying velocity interfaces. Now let the (N– 1)th velocity interface be a non‐ (or badly) reflecting bed, whereas the other interfaces, including the base of the Nth layer, reflect satisfactorily, and let the velocities UN– 1 and UN of the (N– 1)th and Nth layer, respectively, be known. Then the normal moveout velocity for the base of the Nth layer, if known in one direction at a certain part of the surface of the earth, provides a second order differential equation in the horizontal coordinates x and y for the depth ZN – 1(x, y) of the unknown interface.The mathematics becomes rather simple in the case of two‐dimensional geological structures. For this case and N= 2 the differential equation mentioned can be solved by stepwise integration or by iteration. One of the many possible applications of the new concept is the determination of the structure of the base of an overthrusting sheet.
FIELD PROCESSING OF MAGNETIC DATA*
Authors: GREEN R. 
Published: April 2006

AbstractThis paper deals with the practical problem of processing magnetic data in the field, and it shows how the parameters describing a geological contact can be obtained quickly and conveniently on the basis of five measurements. The complete interpretation can be performed in the field using a programmable calculator. For a small ground‐party the method greatly improves the quality of the field‐work and the interpretation of the magnetic data. The method has been applied to the data from a magnetic survey over the Mooki Fault (Gunnedah‐Manilla, N.S.W.), and the results are discussed as an illustration of the efficacity of the method as a field procedure.
ESTIMATION OF THE MINIMUM DENSITY CONTRAST OF A HOMOGENEOUS BODY AS AN AID TO THE INTERPRETATION OF GRAVITY ANOMALIES*
Authors: GOODACRE A.K. 
Published: April 2006

AbstractGoodacre A.K. 1980, Estimation of the Minimum Density Contrast of a Homogenous Body as an Aid to the Interpretation of Gravity Anomalies, Geophysical Prospecting 28, 408–414.The minimum density contrast value for which a homogeneous body will accurately reproduce an observed gravity low can often be used to determine whether the causative body is a low‐density granite batholith or a sedimentary basin. If the minimum density contrast value is large, the anomaly source is probably a sedimentary basin; if it is small, the source may be either a sedimentary basin or a granite batholith. The minimum density contrast method is tested on the Cheshire Basin and the Weardale Granite.
APPARENT RESISTIVITY OF A MULTILAYERED EARTH WITH A LAYER HAVING EXPONENTIALITY VARYING CONDUCTIVITY*
Authors: BANERJEE B. , SENGUPTA B. J. , PAL B. P. 
Published: April 2006

AbstractIf the conductivity of any one of the layers of a horizontally stratified earth varies exponentially with depth with or without a discontinuity at the interface, the corresponding expressions for apparent resistivity for Wenner‐ and Schlumberger‐sounding arrays can be formulated. The general case has been broadly divided into three categories for mathematical simplicity. All previous discussions of this problem can be regarded as particular cases of the present study.
A PARAMETRIC APPROACH TO THE COMPRESSION OF SEISMIC SIGNALS BY FREQUENCY TRANSFORMATION*
Authors: BERESFORD‐SMITH G. , MASON I. M. 
Published: April 2006

AbstractThe compression of seismic signals which have propagated through a dispersive medium can be achieved by a frequency‐domain transformation. This transformation is formally related to the dispersion characteristic of the medium and is independent of phase and group velocities. By defining a suitable cost‐function to measure the degree of dispersion of a time‐ signal, an iterative technique can be employed to find that transformation which gives minimum dispersion.In this paper, we assume that the inverse of the dispersion characteristic can be adequately approximated by a finite polynomial in the region of maximum signal energy density. The coefficients of this polynomial are the parameters of dispersion of the medium. These parameters can be estimated both in the presence of noise and in the case of signals made up of multiple arrivals.The techniques developed in this paper are applied to seismic signals which have been recorded underground by a set of geophones designed to detect and map discontinuities in coal‐seams. Results of dispersion estimation and signal compression are discussed for data collected in the Blackshale seam, Pye Hill Colliery, near Derby, in the United Kingdom.
THE INDUCTIVE RESPONSE OF A HORIZONTAL CONDUCTING CYLINDER BURIED IN A UNIFORM EARTH FOR A UNIFORM INDUCING FIELD*
Authors: OGUNADE S.O. , DOSSO H.W. 
Published: April 2006

AbstractThe inductive response of a conducting horizontal cylinder embedded in a uniform earth is studied using numerical results obtained for an analytical solution for the problem of a conducting cylinder buried in a homogeneous earth for the case of a uniform inducing field. A check of the validity of the numerical results is made by a comparison with analogue model measurements for a number of cases. Numerical results for a range of cylinder radii (a = 1–10 km), depths of burial (d= 0–4 km), conductivity contrasts (σ2= 10−2‐10 Sm−1), and source frequencies (f= 10−1‐10−4 Hz) of interest in the interpretation of magnetotelluric field measurements are presented. The results indicate that for a uniform inducing field the conductivity and depth of burial of a horizontal cylindrical inhomogeneity are best determined through a measurement of the amplitudes Hy, Hz and Ex and the phases φy and Ψx.
RESISTIVITY SOUNDING ON A MULTILAYERED EARTH CONTAINING TRANSITION LAYERS*
Authors: BANERJEE B. , SENGUPTA B.J. , PAL B.P. 
Published: April 2006

AbstractFor curves over a horizontally stratified earth where any of the layers has a conductivity variation proportional to (1 +β·z)N, where β and N are arbitrary constants and z is the depth to the layer, expressions for apparent resistivity for Wenner and Schlumberger sounding are derived. No assumption has been made about the continuity of conductivity at the interface. It is shown that most of the previous investigations in this connection can be regarded as particular cases of the present study.
AN OPTIMIZED TECHNIQUE FOR DETERMINING STACKING VELOCITY FROM SEISMIC REFLECTION DATA*
Authors: KHATTRI K. , VIG P.K. , RAO N.D.J. 
Published: April 2006

AbstractA new method of estimating seismic stacking velocity from reflection seismograms is based on Fibonacci search technique and provides the highest rate of reduction of the interval of uncertainty of the stacking velocity. A review of the Fibonacci search strategy is presented, the application of the method is illustrated with synthetic and field examples.