bluuebunny/crossref_metadata_2025_split huggingface dataset:
THE USE OF GEOPHONE GROUPS TO IMPROVE THE SIGNAL‐TO‐NOISE RATIO OF THE FIRST ARRIVAL IN REFRACTION SHOOTING*
Authors: DENHAM DAVID 
Published: April 2006

AbstractFor a group of n geophones at a single station, a signal‐to‐noise improvement of √n can only be expected when the background noise, between the individual detectors in the group, is completely uncorrected. This paper gives results, from four different sites, for the variation of correlation coefficient with distance between the detectors. It is found that at these locations the geophone spacings required to reduce the correlation coefficient to zero varied from 30 to 300 feet.These results are in agreement with the predictions of the theoretical model of a two‐dimensional isotropic noise field described by Hills and Faran (1952). This model provides estimates of the spacing required between geophones to reduce the correlation coefficient to zero, provided that the velocity of the noise is known and that its spectrum is of a simple form.Often it is impractical to reduce the correlation coefficient to zero because of the large spacing required between the geophones in the group. For this case a simple method is described in which the signal‐to‐noise improvement can be calculated given that the correlation coefficients between the geophones in the group are known. This procedure can easily be used in the field because the correlation coefficients can rapidly be computed from paper records by using Tomoda's method (Tomoda, 1956) which gives values of sufficient accuracy to be used for on‐the‐spot calculation.
CONTRIBUTION AU CALCUL SIMPLIFIE DES CORRECTIONS DE RELIEF A GRANDE DISTANCE EN GRAVIMETRIE*
Authors: NEUMANN R. 
Published: April 2006

AbstractIn a recent paper, H. A. Winkler developed a suitable method for determining longdistance terrain corrections in gravity by interpolation. Such a technique implies that it is necessary to take into account the changes of the correction g not only with the location (X, Y) but also with the elevation Z of a station. Study of the function g(Z) shows that its curve, with amply sufficient accuracy, may be represented as a parabola. Moreover, the parabolas corresponding to different stations are all equal. From these properties a method has been derived which saves computing time and yields long‐distance terrain corrections with convenient accuracy.
EIN NÄHERUNGSVERFAHREN ZUR BERECHNUNG VON GRAVITATIONS‐ANOMALIEN FÜR BELIEBIG GEFORMTE INHOMOGENE MASSEN MIT DEM DIGITAL‐RECHNER*
Authors: SZELÉNYI GY. 
Published: April 2006

ABSTRACTBy this method an approximation of gravity‐anomaly of an inhomogeneous mass with any form is calculated. The mass is inbedded in a homogeneous medium. The density of the medium differs from the density‐distribution of the mass.
AMELIORATION DU RAPPORT SIGNAL / BRUIT A L'AIDE DU FILTRAGE EN EVENTAIL*
Authors: FAIL J. P. , GRAU G. , LAYOTTE P. C. 
Published: April 2006

AbstractCase history of the use of fan filtering for improving reflection continuity without destroying their character. The field technique is described: wide‐band, large dynamical range recording with a programmed gain control and a very slow A.G.C., small distance between trace centers, high cutoff wave‐number.Although the total amount of mixing due to fan filtering is rather high, a broad spectrum was obtained and inverse convolution filtering was used to improve trace resolution.
A METHOD OF QUANTITATIVE INTERPRETATION OF THE ELECTRICAL FIELDS OF INFINITELY LONG SINKS AND HORIZONTAL CIRCULAR CYLINDRICAL BODIES*
Authors: JAIN SUDHIR 
Published: April 2006

AbstractUsing a simple integral transform suggested by Roy and Jain (1961), methods of interpretation of electrical potential data for a point source in the presence of one or two infinitely long horizontal cylinders are developed. The methods are applicable to electrical surveys of long filled channels of semi‐circular cross‐section or of buried cylindrical ore bodies.
SUR LA REPONSE TRANSITOIRE DES FORMATIONS RESISTIVES*
Authors: LOEB J. 
Published: April 2006

ABSTRACTThis paper deals with transient response of resistive formations to pulse sources. Computation of solutions of equations such as:

image

is linked to computation of solutions of equations such as:

image

It can be used in the case where several media exist, the conductivities of which are σ1 σ2.The method consists in establishing a correspondence between the case to be dealt with and a fictitious region of space with the same interfaces, in which the propagation of a disturbance obeys Equation (2).Velocities C1 C2. are related to conductivities by the condition

image

At the interfaces, the distribution of incident energy between transmitted and reflected energy is related to the ratio of characteristic impedances, i.e.
image

in the real case (ω is the angular frequency) and C1/C2 in the fictitious case.These ratios are the same because of Equation (3).Time variation g(θ) of solution of (1) in a given point is computed from time variation of solution of (2) at the same point by means of the transformation

image

(in which τ is the actual time and T the time unit).Equation (4) originates from a formula of symbolic calculus, that allows the Laplace transform of F(Vp) to be calculated from the known Laplace transform of F(p). This correspondence is the one that allows passage from in (1) to in (2)Equation (4) becomes considerably simpler when the response to the unit impulse consists (as happens most often) of the sum of a finite or infinite number of pulses The results is then a sum of functions such as:
image

Hence, this procedure appears as an extension to systems that obey Equation (1) of the image theory very often used when Equation (2) is applied.
ON THE CORRELATION OF GRAVITY WITH TIDAL ANOMALIES*
Authors: GROTEN E. 
Published: April 2006

AbstractTidal deformations of the solid earth show remarkable regional fluctuations. Mean gravity anomalies reveal strong positive correlation with the regional variations in the vertical tide component, if the effect of topography on the gravity field is reduced by isostatic proceedings. The correlation of these “tidal anomalies” with the lower harmonics of the gravity field is weaker. Heterogenities of the upper mantle may be a source of these differences in the deformations.
SECURITE EXAMEN STATISTIQUE DE 1200 ACCIDENTS GEOPHYSIQUES*
Authors: RICHARD H. 
Published: April 2006

ABSTRACTMore than 1200 cards on geophysical accidents have been accumulated since 1957. Classification of these cards into various categories reveals relative stability in terms of time. It is possible to determine a highly significant severity rating for each category. The greatest hazards are explosion and electrocution.
UN NOUVEAU MAGNETOMETRE AERIEN LE MAGNETOMETRE A VAPEUR DE CAESIUM
Authors: GIRET R. , MALNAR L. 
Published: April 2006

ABSTRACTCompagnie Générate de T.S.F. (C.S.F.) has recently developed a new magnetometer based on the optical pumping of caesium vapour.After carrying out a systematic programme of ground and in‐flight tests, Compagnie Générale de Géophysique (C.G.G.) has put several of the airborne models into service.Following a discussion of the fundamental principles involved, the instrument is described and its specifications are given. The two forms of read‐out are: an analog recording, of the conventional type, and a digital version, recorded on magnetic tape.The instrument measures the total intensity of the earth's magnetic field with a sensitivity of 0.03 gamma. Temperature compensation is provided, making possible operation between — 20 and + 45 degrees centigrade. Performance is not affected by an inhomogeneous field as long as the gradient is less than 10 gammas per centimetre.The range of the instrument is from 20,000 to 70,000 gammas and the values are obtained automatically, without the intervention of an operator.There is no danger of instrumental drift, and the selection of caesium vapour and the components of the detector guarantee that the absolute value of the field, throughout the range of the instrument and regardless of the circumstances, is measured to within one gamma.The first large‐scale project making use of these magnetometers, carried out by C.G.G., is the Magnetic Map of France, which has been compiled for the Centre National de la Recherche Scientifique. The characteristics of this project are given.
UTILISATION D'UN CENTRAL DE DIGITALISATION D'ENREGISTREMENTS SISMIQUES*
Authors: MILLOUET J. , MORLET J. 
Published: April 2006

ABSTRACTUntil such time as digital seismic recording techniques are in widespread use in the field and partly because it cannot afford digital equipment, C.E.P. has decided to build a processing system which can digitize and process seismic information in analog form on magnetic tapes.C.E.P. was prompted to adopt the digital technique to enable it to proceed with its stratigraphical investigations, starting with the elaboration of synthetic records and followed by the study of signals and deconvolution.Though the analog form of recording is not too suitable for digital processing owing to its low dynamic range, it seemed to us that it was nevertheless perfectly feasible to enhance the analog information by processing it digitally through an automatic computer.This approach to the problem of data enhancement is more satisfactory than the (conventional) analog method, which is more complicated and less accurate.

The digital processing system comprises:
a magnetic playback system
a two‐channel reproduction device
an analog‐digital converter
a 1620 IBM computer
an automatic plotting device for graphical presentation of results.

Examples of different processing forms are presented:

cancellation of A.G.C. action
computation of seismic signal
deconvolution
correlation techniques
anti‐singing
study of the response of the various items of equipment.

We have come to the conclusion that very interesting results have been obtained in spite of the low dynamic range of the analog tapes.With this equipment it is possible to study and process the data in digital form and compare results with those obtained by analog processing. Also, the experience gained will be very useful when digital field crews start operating.Unfortunately, it is not possible for the time being to operate the equipment on a commercial production basis, but only to develop working methods, to conduct short studies or to guide and control analog processing techniques.At present our efforts are therefore aimed at shortening the time required for processing and plotting.
SEISMIC REFRACTION AND SCREENING BY THIN HIGH‐VELOCITY LAYERS *
Authors: POLEY J. Ph. , NOOTEBOOM J. J. 
Published: April 2006

AbstractThe screening effect of thin, relatively shallow high‐velocity layers often presents considerable problems in seismic exploration. Such layers prevent the greater part of the seismic energy from travelling to greater depths and introduce additional refraction arrivals, confusing the seismogram still further.In order to investigate both the screening and refractive properties of high‐velocity layers, scale‐model experiments have been made over a wide range of layer‐thickness/ wavelength ratios (0.05 < d/λ < 2) for suitably chosen material contrasts. The results may be summarised as follows.Refraction arrivals from thin layers in the field may be recognised by their relatively rapid amplitude decay. Furthermore, the “echeloning”‐effect observed for refraction first arrivals may be due to the presence of a (thin) layered structure. Since the apparent refraction velocity varies with d/λ when d/λ < 1, differences between vertical well‐log velocities and velocities observed along the surface may be expected, making time/depth conversion using surface velocity data inaccurate.Transmission of elastic energy may be expected, if anywhere, only near the shotpoint, at small geophone offset, and for relatively thin screens (d/λ < 0.1). The transmitted signal shape is then independent of the layer thickness. This transmitted energy may be registered either in a reflection set‐up with geophones near the shotpoint, or in long‐distance refraction work.Three possibilities are offered for overcoming the screening effect of thin high‐velocity layers: Use longer‐wavelength signalsApply short‐spread reflection shootingApply long‐distance refraction shootingThe experimental results obtained in scale‐model arrangements of such set‐ups confirm the potentialities of these methods.
IMPORTANCE OF AEROMAGNETICS IN EVALUATION OF STRUCTURAL CONTROL OF MINERALIZATION*
Authors: DOMZALSKI W. 
Published: April 2006

ABSTRACTThe term “structure”, as used here, includes synclinal and anticlinal folds and folding in general, faults, cross fractures and various conditions associated with intrusions. Structure, both regional and local, has a very important role in emplacement of mineralization. Under certain circumstances which occur fairly commonly, structural conditions are reflected significantly in the trends and intensities apparent on aeromagnetic maps. A number of documented illustrations based on Canadian Shield conditions are discussed. Illustrations are drawn from areas of known geology and from proven mining camps, as well as from loci of recent discoveries. Canadian examples are chosen because of existence and availability of extensive aeromagnetic cover, although it is logical to extend the argument to other shields and indeed to regions of other geological, but similar magnetic character.The importance of aeromagnetics in structural approach to exploration and the correctness of such approach seem to be fully substantiated by results discussed.
A THEORETICAL INVESTIGATION ON THE FORMATION FACTOR/PERMEABILITY/POROSITY RELATIONSHIP USING A NETWORK MODEL*
Authors: SCHOPPER JÜRGEN R. 
Published: April 2006

ABSTRACTThe knowledge of hydraulic and electric properties of porous media and the relations between them is essential for the quantitative evaluation of electric well logs and the solution of other reservoir engineering problems. The state of the art in this field is not yet satisfying. Theories still show considerable discrepancies with practice due to oversimplified model approaches. Empirical relations are either too coarse, not fully determined, or valid under specific geological and geographical conditions only. This article deals with the development of a general theory of the electric and hydraulic resistance behavior of porous media on the basis of a very general statistical network model. A general solution of the relations between formation factor, permeability, and porosity is presented by means of a rigorous mathematical treatment of two limiting cases of such a network. The solution shows that the product of the formation factor and the permeability can be expressed in the expectation values and the variation coefficients of pore channel cross section and shape factor and by a network factor, that depends on the mesh texture of the network. This network factor is in the range zero to one. It is further shown that the path length increase enters both the electric and the hydraulic tortuosity by its square.
THE SECTIONAL AUTO‐CORRELOGRAM AND THE SECTIONAL RETRO‐CORRELOGRAM *
Authors: ANSTEY N. A. 
Published: April 2006

ABSTRACTThe auto‐correlation function of a seismic trace contains information on all the multiple reflection activity present in the trace.The interpretation of this information is facilitated by the arrangement of autocorrelation functions in cross‐sectional form, in the manner of a normal record section. This is the concept of the Sectional Auto‐Correlogram.Specifically, the Sectional Auto‐Correlogram will.Show if the record section does not include significant multiples, thus allowing confident picking of the primary reflections.Show if the record section does include significant multiples, giving their travel times and inclinations (and, under certain circumstances, their reflection coefficients).Indicate by what process the multiples should be treated.Yield an authoritative measure of the success of a multiple‐attenuating treatment.Delineate shallow horizons, even those whose primary reflections are too early to be recorded satisfactorily.Give the true travel time of a primary reflector, and the sign of its reflection coefficient.The Sectional Auto‐Correlogram allows the study of primary reflectors by consideration of the multiples generated by them, and in this sense may be said to turn multiple reflections to advantage. Thus a primary reflection at a certain time is defined if we find that every reflection on the record is followed by a multiple after this certain time. Alternatively, a primary reflection at a certain time is defined if, after that certain time, we can find a repetition of the entire record.The Sectional Auto‐Correlogram also has secondary uses in fault identification, crustal studies and weathering problems.
ω‐k FILTER DESIGN*
Authors: WIGGINS RALPH A. 
Published: April 2006

ABSTRACTTwo‐dimensional band‐pass filters can be constructed by a simple extension of the theory of one‐dimensional band‐pass filters. Similarly to the one‐dimensional analogue the shape of the two‐dimensional filter is important in determining its effectiveness. The band‐pass filter formulation can be further refined so that the filter will concentrate its rejection energies in certain areas of the ω, k plane. Such band‐pass, band‐reject filters are found by solving a set of simultaneous equations.
TWO COMPUTER PROGRAMS FOR THE CALCULATION OF STANDARD GRAPHS FOR RESISTIVITY PROSPECTING*
Authors: ARGELO S. M. 
Published: April 2006

AbstractThis paper includes publication of two algorithms, to be processed on a digital computer. The algorithms are based upon the two mathematical denotations, presented by Dr. J. C. van Dam in this same issue. The computer programs are written in Algol, in the form of procedures (i.e. subroutines to be activated from a surrounding Algol program).Each of the two procedures is preceded by a numerical analysis. Some remarks are made about the reliability of each of the two procedures, the production and the computing time required.
LA GRAVIMETRIE DE HAUTE PRECISION APPLICATION AUX RECHERCHES DE CAVITES*
Authors: NEUMANN ROBERT 
Published: April 2006

ABSTRACTHigh precision gravity surveys have to be examined at different points of view: the accuracy which one can expect on the final results, regardless to their distribution, the shape and amplitude of the expected anomalies, depending on these factors, which grid of stations is convenient in each particular case.Under certain condition, using an appropriate procedure, involving strict criteria, it is possible to get on the Bouguer map the same accuracy as the reading one.However an accuracy closed to 0,01 mgal does not imply that anomalies as 0,01 or 0,02 mgal deserved attention. Numerous factors limit our appreciation of significant anomalies to 0,05 mgal, may be a little less.When cavites are concerned, it is always necessary to define the extreme dimensions an depth of volumes which may give detectable anomalies.Some example are given illustrating different aspects of this particular type of geophysical prospecting.
FITTING OBSERVED PROFILES TO A MAGNETIZED DYKE OR FAULT‐STEP MODEL*
Authors: POWELL D. W. 
Published: April 2006

ABSTRACTThe symmetry shown, by the function describing the magnetic anomaly due to a dyke or vertical fault step leads to a method by which an observed profile may be adjusted to conform with that symmetry. By making these adjustments a minimum the ideal dyke or fault profile closest to the observations is constructed. In three of four possible situations this is interpreted by simple geometry.Parallelpiped models may be transformed into two dykes for symmetry analysis. Depth limited models are not so amenable, even in special cases.
SOURCES OF ERROR IN A SEISMIC DIGITAL RECORDING SYSTEM*)
Authors: DONNELL W. F. 
Published: April 2006

ABSTRACTThe use of digital recorders and computers in seismic exploration promises major enhancement of the quality of final documents available to interpreters. The ultimate objectives of recording and processing remain what they always have been:1 Record the reflection wavelet as a function of time; this requirement has been met with satisfactory accuracy for a number of years.2. Record the reflection wavelets with sufficient fidelity to permit the interpreter to recognize them.Various factors affect our ability to achieve this second objective. Certain recording errors are associated with digital recording systems. However, an understanding of the sources of error will enable the operator to use his system properly and to estimate the noise level or inaccuracy of field recordings. Field operations do not require rigorous error analysis; in most cases a satisfactory approximation can be obtained from simple calculations.Three types of “noise”–seismic, instrument and power line–introduce errors. Factors which contribute to over‐al recording system error include specifically input noise, power supply ripple, crosstalk, A‐D conversion error, quantizing noise, aliasing, distortion. Examination of each component of a recording system, permits the determination of its ultimate effect on the over‐all noise level–or error level–of the entire system.Many of the error sources produce statistically independent noise which is not correlative. Where this is true, error voltages from various sources may be combined by taking the square root of the sum of the mean square noise voltages, giving a result slightly greater than the largest single voltage if one source is much greater than any other source. This simplification can be used to estimate over‐all system noise levels. Distortion and crosstalk depend on signal amplitude and should be added algebraically in each category. Each final sum should be used as a statistically independent noise source with respect to other system noise sources.Using the foregoing examples and simplified system for estimating over‐all system noise, and assuming that much of the distortion (which limits signal/instrument noise ratio to 54 db) can be removed by filtering, we determine that the combined effect of all sources of error is to reduce the system S/N ratio to approximately 74 db.With proper care digital field recording systems can produce very good field records, and exotic computer processes can enhance signal and reduce various forms of noise. However, one always must recall that the level of confidence which one can place in an interpretation of seismic data must be dependent on a knowledge of the accuracy of the basic data.
USE OF EXPECTED ERROR IN THE DESIGN OF LEAST‐SQUARES OPTIMUM FILTERS*
Authors: WIGGINS RALPH A. 
Published: April 2006

ABSTRACTThe design of least‐squares optimum filters is based upon minimizing a suitably defined error criterion. The expected value of this error is easily computable after the coefficients of the filter have been determined.When a particular filtering problem is specified, there are several parameters which are specifically not included in the optimization procedure. However, the magnitude of the expected error may be quite sensitive to these parameters. The examination of the relative values of the expected error for variations of these unspecified parameters may lead to a better definition of the filter problem.The parameters which are left unspecified by the general least‐square filter definition include:1. The addition of white noise to the signal autocorrelation to stabilize the filter behavior.2. The specification of the shape of the desired output of the filter.3. The specification of the lag between the desired output and the input.Examples are given showing the relationship between these parameters and the value of the expected error.