bluuebunny/crossref_metadata_2025_split huggingface dataset:
ARRAYS AND NOMOGRAMS FOR ELECTRICAL RESISTIVITY EXPLORATION*
Authors: MEIDAV TSVI 
Published: April 2006

AbstractA number of electrical resistivity arrays are available to the exploration geophysicist in the conduct of vertical or horizontal profiling. The advantage of using central‐type arrays which produce large potential drops, such as the Wenner or the Schlumberger, must be weighed against the ease of acentral arrays such as the polar and equatorial arrays.A series of nomograms has been designed to provide a means of rapid calculation of the potential drop to be obtained by any of the various central and acentral arrays, as a function of apparent resistivity, electrode spacings and available transmitter power. The same nomograms may also be used for approximate computation of the apparent resistivities in routine surveys. However, the accuracy of resistivity calculation is directly related to the accuracy of drawing lines between the scales and hence is rather limited in reduced‐size nomograms in this paper.
A PULSE COMPRESSION TECHNIQUE USING COHERENT LIGHT*
Authors: BARBIER M. , POULEAU J. 
Published: April 2006

RésuméLes méthodes sismiques à signaux longs du type Vibroseis réclament un traitement qui consiste en la crosscorrélation des signaux reçus avec le signal émis. Cette opération qui est effectuée par des ordinateurs puissants, équipés de convolueurs, est aussi réalisée de manière analogique. Lorsque le volume des données à traiter devient trés important comme c'est le cas en sismique marine, il peut être intéressant ?avoir recours au principe décrit dans cet article, qui utilise une source de lumière cohérente. Une étude de la dyna‐mique et des exemples synthétiques sont montrés.
MAGNETOTELLURIC SOUNDING ON A LAYERED EARTH WITH TRANSITIONAL BOUNDARY*
Authors: MALLICK K. 
Published: April 2006

AbstractThis work deals with a theoretical investigation of the magnetotelluric sounding where the horizontal layers of a geological section do not have a sharp but a transitional boundary. The ratio of the horizontal electric to the horizontal magnetic components gives a measure of “Cagniard impedance”, which together with the phase relationship between them, enables one to determine the subsurface geometry and the true resistivities.Utilising the principle of similitude a set of Resistivity Master Curves and the corresponding phase relationships are presented here for the case where the lower half‐space is infinitely resistive. The relation between the relative transition thickness and the cut‐off period is illustrated.
APPROXIMATION OF THE GRAVITATIONAL ATTRACTION OF GEOLOGICAL BODIES*
Authors: BOTEZATU R. , VISARION M. , SCURTU F. , CUCU G. 
Published: April 2006

AbstractThe gravitational attraction produced by a geological body of irregular shape can be easily determined by dividing it into cubes of small size. The exact expression of the effect of a cube is very complicated, but it can be calculated by using an electronic computer.4851 values of the gravitational attraction were determined for different positions of a cube with the side of 2l and the center in M(x0, y0, z0), for x0∈[0;20], y0∈[0;20] and z0∈[0;10]. Using these values, templates in double logarithmic representation were drawn, with x0 and z0 as parameters and y0 as abscissa, and with x0 and y0 as parameters and z0 in abscissa; this double set of templates permits a good interpolation for all cubes in the considered domain of M.The use of templates was tested to approximate the effect produced by a theoretical model of spherical shape and in a real case of a three‐dimensional salt body of known shape based on a large number of boreholes. In both cases very good results were obtained.
MULTICOVER MEASUREMENTS IN REFRACTION SHOOTING*
Authors: HIRSCHLEBER U. 
Published: April 2006

AbstractMulticover measurements in refraction shooting are comparable to long‐spread reflection shooting. Of course, spread length, distance of traces and offset may be larger than in reflection shooting and depend on the, depth, the velocity and the dipping of the refractors to be detected. For later processing an equation for the refractor velocity is derived in case of flat and steep dipping refractors. The depth and the angle of dip will be computed from delay times. An outlook to digital processing is given.
THE USE OF COMPUTER GRAPHICS IN GRAVITY INTERPRETATION*
Authors: ARAB N. 
Published: April 2006

AbstractComputer‐Graphics, the visual display of data in digital and analog form, allows immediate interaction between man and machine. This interaction facility is valuable when the user is engaged in model design. By using such a device in gravity interpretation, the geophysicist can overcome the slow process of model simulation constrained by the conventional input/output devices, also maximum control over running programmes can be exerted if needed.
RESISTIVITY ANALYSIS FOR MODELS OF A SPHERE IN A HALF‐SPACE WITH BURIED CURRENT SOURCES*
Authors: MERKEL R. H. , ALEXANDER S. S. 
Published: April 2006

AbstractBoundary‐value problems in steady‐state current flow were solved numerically in bispherical coordinates for a sphere of arbitrary conductivity in a half‐space. Solutions for the potential on the surface of the half‐space were examined for the cases where both current sources were on the surface, one source on the surface and the second between the surface and the sphere, and one source on the surface and the other in the sphere. Results show a great similarity with the layered case when the buried electrode is placed between the surface and the conducting region. Such a buried electrode configuration makes it possible to obtain an accurate measurement of the depth to the conductor in both cases. A model with the current electrode placed in a conductive sphere is compared with a three‐layered model with the source in a conductive intermediate layer, and results indicate that the lateral extent of a finite anomalous zone can be estimated using these limiting curves. The validity of these theoretical calculations for buried spheres was confirmed experimentally by tests conducted on an analog model.
ABOUT A METHOD OF REPRESENTATION OF IP‐VALUES OBTAINED OVER SEDIMENTARY FORMATIONS (TWO LAYER CASES).*
Authors: MONGELLI F. , PATELLA D. 
Published: April 2006

SummaryAn operative technique is described along with a method of representation of Induced Polarization values obtained over homogeneous rocks against the electrical power per unit volume.The results of similar experiments over two‐layer ground, are shown according to the same operative technique and method of representation.With the method of representation suggested in this paper it is possible to distinguish discontinuities and to get information about the thickness of the upper medium.
THERMAL NEAR‐SURFACE EXPRESSION OF SHALLOW GEOLOGICAL FEATURES*
Authors: POLEY J. PH. , VAN STEVENINCK J. 
Published: April 2006

AbstractIt has been customary in geothermal studies to assume the surface to be an isothermal plane, though difficulties existed to explain the magnitude of thermal anomalies observed in the field under this assumption. Detailed investigations of temperatures at depths between 5 cm and 230 cm show that—after removal of the strong diurnal variations—sizeable anomalies persist right to the surface. Thus, the effective heat transfer (coefficient) at the surface might be lower than commonly assumed.
ADAPTIVE SIGNAL PROCESSING THROUGH STOCHASTIC APPROXIMATION*
Authors: WANG R. J. , TREITEL S. 
Published: April 2006

AbstractOne of the problems in signal processing is estimating the impulse response function of an unknown system. The well‐known Wiener filter theory has been a powerful method in attacking this problem. In comparison, the use of stochastic approximation method as an adaptive signal processor is relatively new. This adaptive scheme can often be described by a recursive equation in which the estimated impulse response parameters are adjusted according to the gradient of a predetermined error function.This paper illustrates by means of simple examples the application of stochastic approximation method as a single‐channel adaptive processor. Under some conditions the expected value of its weight sequence converges to the corresponding Wiener optimum filter when the least‐mean‐square error criterion is used.
OPTIMUM DIGITAL FILTERING AND INVERSE FILTERING IN THE FREQUENCY DOMAIN*
Authors: DEREGOWSKI S. M. 
Published: April 2006

AbstractTwo distinct filters are developed in the frequency domain which represent an attempt to increase the resolution of fine structure contained in the signal whilst keeping the expected filtered noise energy within reasonable bounds. A parameter termed the White Noise Amplification is defined and used together with a measure of the deconvolved pulse width in order to provide a more complete characterisation of the filters. Each of the two main types of frequency domain filters discussed varies in properties with respect to a single adjustable parameter. This may be contrasted with a time domain Wiener filter which in general has three variables: length, delay and an adjustable noise parameter or weight. The direct frequency domain analogue of the Wiener filter is termed a gamma‐Fourier filter, and is shown to have properties which span the range from those of a spiking filter with zero least square error at one extreme, to those of a matched filter at the other extreme of its variable parameter's range. The second type of filter considered—termed the modulated Gaussian filter—is similarly shown to be a perfect spiking filter at one extreme of its parameter range, but adopts the properties of an output energy filter at the other extreme.
CORRECTION OF ACCURATE GRAVITY SURVEYS BY CAREFULLY OBSERVED VERTICAL GRADIENTS OF GRAVITY*
Authors: THYSSEN‐BORNEMISZA S , GROTEN E. , BAZHAW W. O. 
Published: April 2006

AbstractGravity surveys in western Texas with station spacing of about 400 m were complemented by carefully observed vertical gradients of gravity making use of specially designed and automated instrumentation. The presented areal surveys of 51 and 52 stations taken in relatively flat terrain are parts of a large survey of close to 1000 stations complemented by an equal number of vertical gradient measurements. Quite irregular anomalous vertical gravity gradients surpassing 10 microgal/m were often encountered. Assuming the causative density contrasts to be located not more than 10 m below ground surface then free air correction errors of ± 0.1 mgal and more must be accepted. From a practical point of view there seems to be no other way to control such unpredictable errors than to carefully observe the local variation of vertical gravity gradients with adequate equipment. Making use of very closely spaced gravity measurements to derive these anomalous features seems more costly and cumbersome.
SEISMIC NOISE MEASUREMENTS IN A GEOTHERMAL AREA*
Authors: GOFORTH T. T. , DOUZE E. J. , SORRELLS G. G. 
Published: April 2006

AbstractGeneration of electrical power through the use of natural steam obtained from the Earth has the potential to be a significant source of pollution‐free power. Successful future exploitation of geothermal power depends upon the development of cost‐effective exploration techniques. A field experiment in the Imperial Valley of California indicates that there is a close empirical relationship between hot water deposits at depth and an anomalously high seismic background level at the surface. If this relationship proves to be a general one, it will serve as the basis of a simple and inexpensive method of geothermal exploration.
RESISTIVITY PROFILES OVER SOME DYKES OF DHANBAD*
Authors: SINGH J. , JHA B. P. 
Published: April 2006

AbstractA number of resistivity profiles over dolerite and metadolerite dykes have been taken using Wenner and Schlumberger configurations around Dhanbad in order to find the potential of these for water accumulation. These dykes give rise to both resistivity highs and lows as compared to the background. The results are discussed in the light of known theories. Some suitable sites for water accumulation have been delineated.
“REMOTE SENSING”— AN EVALUATION OF ITS IMPACT ON EARTH SCIENCE—*
Authors: CASSINIS R. 
Published: April 2006

Summary“Remote sensing” techniques have been used for many years as an exploration tool; broadly speaking, any method using sensors not directly connected to the earth's surface falls into this group.It is preferable, however, to use the term solely with reference to a number of new sensors which have recently become available to earth scientists for the detection of various radiations of the electromagnetic spectrum in the wave length range from 0.1 micron (UV) to some centimeters including the visible and infrared regions.Radiations artificially induced in the earth (active sensing) or spontaneous radiations (passive sensing) can be detected. Some of the bands investigated seem promising for application to geological surveys, especially using sensors on aircraft and satellites, which allow synoptic and large scale investigations.A brief account is given of the results already achieved and of future developments such as the ERTS and manned satellite (post Apollo) “earth observation” programmes.The potential role of Europe in the field is discussed.Details are given of some applications of thermal I.R. imagery to geological and vulcanological problems, with special emphasis on the research carried out in Italy.
LES COURBES DAR ZARROUK ET LES SONDAGES DIFFÉRENTIELS DE RÉSISTIVÉ*
Authors: SZARANIEC E. 
Published: April 2006

AbstractDifferential and difference soundings of resistivity for real, imaginary and complex values of the newly introduced parameters ν and μ are considered. The transverse and longitudinal differential soundings, known up to the present, correspond with the values ν= 1 and ν=— 1.The point of departure is the generalization of the concept of Dar Zarrouk parameters and the dimensional analogy between D.Z. resistivity and transverse and longitudinal differential resistivities. Properties of generalized D.Z. curves as well as the method of their construction are given. The examples of differential and difference curves are presented and the properties of these curves are discussed; particulary the effective spacings are determined. The problems of the realization of differential and difference soundings are considered; the bisymmetrical and asymmetrical arrays are proposed as a practical ones.
THE EFFECTS OF ANISOTROPY ON SQUARE ARRAY RESISTIVITY MEASUREMENTS*
Authors: HABBERJAM G. M. 
Published: April 2006

ABSTRACTAn account is given of the use of the square array technique in investigating the surface effects of rotational anisotropy when the axes of anisotropy are inclined to the surface. It is shown that, as with other arrays, two anisotropy parameters and n can be derived by varying the array orientation.On the basis of these considerations, the effects of such anisotropy on the values of the mean apparent resistivity and azimuthal inhomogeneity ratio normally obtained in square array measurements is reviewed.Particular attention is paid to the variation of resistivity with orientation and it is noted that, in areas of moderate anisotropy, this variation is lower for the square than for the Schlumberger array.In addition to this advantage, the azimuthal inhomogeneity ratio obtained from square array measurements may be used to indicate the severity of anisotropy in an area and two field examples of this use are given.Where anisotropy is severe, gross variations of apparent resistivity with orientation are obtained with either square or collinear arrays. In these circumstances, the use of crossed measurements is considered and the particular stability of the crossed square array demonstrated.
RESISTIVITY SOUNDING ON A THREE‐LAYER TRANSITIONAL MODEL*
Authors: JAIN S. C. 
Published: April 2006

AbstractThe expression for the potential due to a point source of current, placed on the surface of a horizontal three‐layer earth, has been derived when conductivity in the second layer varies linearly with depth and changes abruptly at the boundaries. Master curves for Wenner and Schlumberger configurations have been presented for an insulating basement and for one value of conductivity gradient in the second layer.
ELECTRICAL SOUNDING ON THE WATER SURFACE AT KHOR KUNDI EL‐BAHARI IN EGYPT*
Authors: BOULOS F. K. 
Published: April 2006

AbstractElectrical resistivity sounding was attempted with success in 1960 on the surface of the Nile water in Khor Kundi El‐Bahari, the starting place for the construction of the offset channel of the High Dam. The method was applied to determine the depth to the upper surface of the granite below the alluvium and Nile water. The success of the method conducted at two stations in the Khor is attributed to the favourable geological conditions of the section which consists of nearly homogeneous layers besides the good earthing conditions of electrodes dipped in water. The high resistivity contrast between water and granite facilitates interpretation of sounding curves. Factors interfering with the results of interpretation are mentioned.
DEPTH OF INVESTIGATION IN WENNER, THREE‐ELECTRODE AND DIPOLE‐DIPOLE DC RESISTIVITY METHODS*
Authors: ROY A. 
Published: April 2006

AbstractUsing a method and definition given earlier (Roy and Apparao, 1971), this paper computes the depths of investigation in homogeneous ground for (a) the Wenner α, β and γ configurations, (b) the three electrode system and (c) the dipole‐dipole arrangements when the dipole lengths are not infinitesimally small. The results for (a) and (b) have been summarised in a table, while those for (c) are shown as contour diagrams. In all the dipolar arrangements examined in this paper, except the equatorial, the depth of investigation decreases (and the vertical resolution increases) with increase in any or both of the dipole lengths. For the equatorial set up, this decrease (or increase) is very small.
RESISTIVITY MEASUREMENTS IN VALLEYS WITH ELLIPTIC CROSS‐SECTION*
Authors: MUNDRY E. , HOMILIUS J. 
Published: April 2006

AbstractIn this paper an idealized valley of a semi‐elliptic cross‐section is considered. For a Schlumberger configuration on the axis, sets of master curves are calculated for the ratio of semi‐axis a/b= 1, 2, 3, 4, 5 in corresponding to various resistivity ratios of surrounding rocks and valley sediments. For small resistivity ratios, these model curves have the shape of three‐layer curves for horizontal bedding and are often equivalent to them within the accuracy of measurements. The axial ratio a/b considerably affects the depth determination of valley sediments. In the special case of a circular cross‐section (a/b= 1) the influence of the position of the electrodes on the sounding curve is studied in more detail.The application of the master curves in practice shows that the influence of the specific shape of the valley on soundings should not be neglected. In general, the valleys have a greater “true” depth than can be seen from the interpretation of a sounding by master curves corresponding to the horizontal bedding.
MAGNETIC SUSCEPTIBILITY ANISOTROPY OF VARIOUS ROCK TYPES AND ITS SIGNIFICANCE FOR GEOPHYSICS AND GEOLOGY*
Authors: JANÁK F. 
Published: April 2006

AbstractIn the interpretation of magnetic anomalies and in paleomagnetism, the anisotropy of magnetic susceptibility is commonly neglected. Nevertheless, this property has basic significance, because, owing to susceptibility anisotropy, the directions of the vectors of induced and remanent magnetization are deflected from the direction of the Earth's magnetic field. Almost all rock types investigated possess higher or lower degree of the susceptibility anisotropy. Effusive and sedimentary rocks have the lowest degree of anisotropy. For the latter, the “masking effect” of the paramagnetic mineral components has some influence on the anisotropy degree due to the low mean susceptibility of sedimentary rocks. Metamorphic and plutonic rocks usually exhibit a considerable degree of anisotropy. The highest degree of anisotropy has been found in the rocks containing ferromagnetic minerals with mimetic fabric.The dependence of the degree of the susceptibility anisotropy on the degree of metamorphism proved to be very complicated; of the rock sequence from slates to gneisses, the transient rocks (roofing slates and mica‐schist‐gneisses) showed the highest degree of anisotropy. This result can be used in geology for reliable determination of these rock types.
SIGNAL ENHANCEMENT OF VIBRATORY SOURCE DATA IN THE PRESENCE OF ATTENUATION*
Authors: GURBUZ B. M. 
Published: April 2006

AbstractAmplitude spectra of input FM signals used in the vibratory source method of seismic exploration often show undesirable oscillations near the initial and terminal frequencies. These oscillations have an effect on the correlation background and distort the output signal. Considerable improvement in reducing the amplitude of these oscillations is obtained using a proper taper fuction. Attention is given to the relation between the tapering time and bandwidth of the spectrum.Analyses of the spectra of the received data from vibratory sources show considerable attenuation in comparison with the original field sweep. Since the matched filtering process will result in a series of waveforms which have the shape of the autocorrelation of the input signal, consideration is given to the autocorrelation function and its zero‐lag coefficient of the FM signal in the presence of attenuation. A method has been developed which compensates for the attenuation and recovers the distortion of waveforms when the received data is correlated.The design of a waveform shaping filter for vibratory source data is given to reduce the influence of phase distortion on the received waveforms as well as to increase S/N ratio resolution. Parameters used for this filter are based on the properties of the FM signal and its autocorrelation function.Several examples from field data are presented to illustrate the methods. The results indicate that the use of the above techniques yields sections with good frequency resolution and improved S/N ratio.