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- Volume 20, Issue 3, 1972
Geophysical Prospecting - Volume 20, Issue 3, 1972
Volume 20, Issue 3, 1972
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ANALYSE SEQUENTIELLE*
By P. BOISAbstractVarious authors have recently studied the Walsh and Hadamard transforms for functions with one or two variables. Like the Fourier transform they may be obtained by using the Cooley‐Tukey algorithm. They can be calculated all the faster because Walsh functions have only values equal to + 1 or − 1. The complex number multiplications in the Fourier transform are replaced by additions and subtractions of real numbers.
These transforms are more general than that of Fourier because the concept of sequency, i.e. the mean number of zeros per time unit, is substituted for that of frequency.
These transforms already have numerous applications to signal transmission. We describe some in the field of seismic prospecting, in particular the compression of the information contained in seismic traces.
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TURAM INTERPRETATION BY CURVE MATCHING USING A LINE CURRENT APPROXIMATION*
By K. DUCKWORTHAbstractThe interpretation of Turam data is treated by means of a development of the conventional approach to this type of data. The development consists of a curve matching technique based upon a line current approximation to the true induced current pattern.
The technique requires computation facilities which are readily available in modern programmable calculators.
Practical examples of the use of the method illustrate that it can reveal information concerning the geometry of a conducting body which would not be gained by the conventional approach.
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DIGITAL PROCESSING OF REFRACTION DATA STUDY OF FIRST ARRIVALS*
Authors R. PERALDI and A. CLEMENTAbstractIt has been necessary to resort to the use of “long‐line” refraction marine operations in certain areas where it proved impossible to eliminate singing from reflection records despite the number and variety of programs at our disposal for this purpose.
Experience has shown that manual processing of offshore refraction records takes a disproportionate length of time in comparison with the surveys themselves, and this is incompatible with the requirements for choosing the site of an exploration well. It thus became necessary to find an “industrial approach” to the solution of this processing problem.
It was apparent that automatic picking could also facilitate the interpretation of land refraction data, and that in the case of both marine and land work the interpretations would be more accurate when factors were taken into account which could not be considered when working without the aid of a digital computer.
For these reasons a set of programs was developed for automatic picking and interpretation of refracted arrivals.
The picking itself consists in searching for the maximum values of the normalized cross‐correlation functions of the traces with a “model” trace. The first results thus supplied are: “picked” times, intercept times, maximum values of the correlations, and the values of the tie constants between overlapping spreads.
Next, the construction of the relative intercept time curves is performed; a statistical analysis of these curves then allows the determination of the offset distance.
From these elements,
⊙ either the delay time curve is produced, after ensuring correct reciprocal times by means of additional minor corrections.
Such work is carried out in order to enable the geophysicist to gain a sound idea of the quality of the interpretation. To assist in this aim, part of the trace on both sides of the pick is plotted on the final documents. Valid groupings of several traces involving the same amount of refraction data are thus possible.
⊙ or the refractor depth is constructed with the wavefront method, making use of the relative intercept times.
Such a procedure, which is normally applied to first breaks, can also be used for later arrivals exhibiting slight interference and should represent an important step towards processing secondary arrivals with high interference.
The development of this package, in response to a need which is shared by both SNPA and CGG, is the result of the joint efforts of the Geophysical Group of SNPA's Pau Research Center and CGG's Technical and Scientific Departments.
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THE KALMAN FILTER AS A PREDICTION ERROR FILTER*
Authors N. OTT and H. G. MEDERAbstractIn mathematical statistical filtering the deconvolution problem can be solved by two different methods:
- 1 by inverse filtering
- 2 by calculating the prediction error.
Both methods are well known in the theory of Wiener filters.
If, however, the generating process of the signal is known and can be described by a set of linear first order differential equations, then the Kalman filter can also be used to solve the deconvolution problem. In the case of the inverse filtering method this was shown by Bayless and Brigham (1970). But, while their method can only be used if the original signal is a colored random process, this paper shows that in the case of a white process the prediction error filtering method is a more appropriate approach. The method is extremely efficient and simple. This can be demonstrated by an example which maybe of special interest for seismic exploration.
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AN INTERPRETATION THEORY FOR INDUCED POLARIZATION VERTICAL SOUNDINGS (TIME‐DOMAIN)*
By D. PATELLAAbstractIn this paper it is shown how one may obtain a generalized Ohm's law which relates the induced polarization electric field to the steady‐state current density through the introduction of a fictitious resistivity defined as the product of the chargeability and the resistivity of a given medium.
The potential generated by the induced polarization is calculated at any point in a layered earth by the same procedure as used for calculating the potential due to a point source of direct current.
On the basis of the definition of the apparent chargeability ma, the expressions of ma for different stratigraphie situations are obtained, provided the IP measurements are carried out on surface with an appropriate AMNB array. These expressions may be used to plot master curves for IP vertical soundings.
Finally some field experiments over sedimentary formations and the quantitative interpretation procedure are reported.
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ENHANCEMENT OF ELECTROMAGNETIC ANOMALIES BY A CONDUCTING OVERBURDEN*
Authors V. K. GAUR, O. P. VERMA and C. P. GUPTAAbstractThe effect of a conducting overburden on the electromagnetic response of sulphide ore‐bodies has been studied with the help of quantitative electromagnetic model experiments. These experiments were conducted at a fixed, crystal controlled, frequency of 100 kHz using a number of transmitter‐receiver configurations, though the results discussed here mostly pertain to a horizontal coplanar system. An analysis of the anomaly profiles—after accounting for the regional anomaly—indicates a general enhancement of the response. This is attributed (a) to the concentration of the current lines in the host‐rock effected by the embedded target and (b) to the change in the phase and space orientation of the field vectors, brought about by the conducting overburden. The enhancement is most pronounced in the case of non‐symmetrical bodies such as veins and ribbon‐like structures represented by sheet models, but is also observed to a lesser degree for isometric structures. These results are expected to pave the way for a more accurate interpretation of the induction prospecting data.
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COMPUTER CALCULATION OF RESISTIVITY PSEUDOSECTIONS OF A BURIED SPHERICAL CONDUCTOR BODY*
By E. F. SCURTUAbstractThe use of the electrical image method in calculating the potential of a source in the presence of a buried conductive sphere proves to be difficult because of the great number of terms making up the potential formula. The disadvantages contained by this method are avoided here by resorting to the theory of graphs. In view of this aim the “propagation” of the electrical images due to the sphere has been represented by an infinite graph to which an infinite matrix has been attached.
Taking this as a basis several FORTRAN IV programs for the computation of resistivity pseudo‐sections for various electrode configurations have been coded, and a great deal of such pseudo‐sections have already been calculated with an IBM‐360 computer. Using these results, recommendations regarding both the methodology of the geoelectrical prospecting of spherical shaped conductors and the most suitable way of building resistivity pseudo‐sections are developed.
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COMPARISON OF TIME, FREQUENCY, AND PHASE MEASUREMENTS IN INDUCED POLARIZATION*
Authors K. L. ZONGE, W. A. SAUCK and J. S. SUMNERAbstractIn comparing the similarity between time, frequency, and phase measurements as used in the induced polarization method of geophysical prospecting, parameters must first be defined and the basis for comparison established. The conditions for mathematical equivalence then follow in a natural sequence. Laboratory measurements are made on a variety of rock samples to indicate the type of comparison and correlation expected from field measurements.
Results indicate that frequency domain and phase measurements are equivalent, but two frequency domain measurements are needed to produce the same amount of polarization information as a single phase measurement. Frequency and time domain measurements will be similar but never equivalent due to the basic differences in their respective parameter definitions.
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ECHO‐LOG — EIN GEOPHYSIKALISCHES MEßVERFAHREN ZUR BESTIMMUNG VON FORM VON AUSSOLUNGSHOHLRÄUMEN IM SALZGEBIRGE*
More LessAbstractMit der vorliegenden Arbeit wird das Echo‐Log als ein geophysikalisches Meßverfahren zur Bestimmung von Form und Volumensverteilung von Aussolungshohlräumen im Salzgebirge vorgestellt. Hierzu werden neue terminologische Begriffe wie Echo, Echostrahl, Echostrahler, Echozeit, Echogramm usw. erläutert. Weiter wird über die Meßausrüstung, Durchführung der Vermessung sowie die Ergebnisdarstellung berichtet.
In einem letzten Abschnitt wird zwischen Echos, die auf einem direkten Weg von der Hohlraumfläche zurückgeworfen werden und anderen bei der Registrierung erfaßten Empfangssignalen unterschieden.
In this paper the Echo‐Log is presented as geophysical measuring method for determining form and volume spread of leached cavities in salt formations. Therefore, new terminological definitions like Echo, Echo Beam, Echo Transducer, Echo Time, Echogram etc. will be explained. Furthermore, also the measuring equipment, execution of a survey and the presentation of the results will be described.
In the last paragraph the difference between Echo directly reflected from cavity walls and other in the cavities registered signals will be discussed.
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APPLICATION DU FILTRE DE KALMAN A LA NAVIGATION*
By J. P. FAILAbstractThis paper is concerned with an application of the Kalman filter to integrated navigation systems. It is shown that this filter is well adapted to resetting the dead‐reckoning position by means of a radio‐hyperbolic system or of a Doppler sonar. The algorithm can also be used for resetting the dead‐reckoning position by means of a satellite navigation system.
The first part is briefly concerned with stochastic processes and system theory. The canonical equations for navigation problems are written. The second part is devoted to the Kalman filter. The third part discusses the application of the algorithm to navigation problems and presents some simulation results.
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PARAMETER OPTIMIZATION OF VELOCITY DEPTH FUNCTIONS OF GIVEN FORM BY USE OF ROOT‐MEAN‐SQUARE VELOCITIES*
By R. MARSCHALLAbstractFrom seismic surveys zero offset reflection times and root‐mean‐square velocities are obtained. By use of Dix‐Krey's formula, the interval velocities can be calculated.
If no well velocity survey exists, the interval velocities and T(o) times are the only available information. The suggested way to get a regionally valid velocity distribution is to select N“leading horizons”, where a major change in the velocity parameters occurs and to compute the parameters of the selected velocity depth function (in most cases linear increase with depth) by a special approximation for the interval between two adjacent “leading horizons”.
Herewith all reflection horizons within the interval are taken into account.
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Volumes & issues
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Volume 72 (2023 - 2024)
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Volume 71 (2022 - 2023)
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Volume 70 (2021 - 2022)
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Volume 69 (2021)
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Volume 68 (2020)
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Volume 67 (2019)
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Volume 66 (2018)
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Volume 65 (2017)
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Volume 64 (2015 - 2016)
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Volume 63 (2015)
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Volume 62 (2014)
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Volume 61 (2013)
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Volume 60 (2012)
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Volume 59 (2011)
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Volume 58 (2010)
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Volume 57 (2009)
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Volume 56 (2008)
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Volume 55 (2007)
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Volume 54 (2006)
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Volume 53 (2005)
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Volume 52 (2004)
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Volume 51 (2003)
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Volume 50 (2002)
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Volume 49 (2001)
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Volume 48 (2000)
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Volume 47 (1999)
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Volume 46 (1998)
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Volume 45 (1997)
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Volume 44 (1996)
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Volume 43 (1995)
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Volume 42 (1994)
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Volume 41 (1993)
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Volume 40 (1992)
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Volume 39 (1991)
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Volume 38 (1990)
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Volume 37 (1989)
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Volume 36 (1988)
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Volume 35 (1987)
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Volume 34 (1986)
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Volume 33 (1985)
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Volume 32 (1984)
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Volume 31 (1983)
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Volume 30 (1982)
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Volume 29 (1981)
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Volume 28 (1980)
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Volume 27 (1979)
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Volume 26 (1978)
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Volume 25 (1977)
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Volume 24 (1976)
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Volume 23 (1975)
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Volume 22 (1974)
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Volume 21 (1973)
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Volume 20 (1972)
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Volume 19 (1971)
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Volume 18 (1970)
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Volume 17 (1969)
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Volume 16 (1968)
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Volume 15 (1967)
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Volume 14 (1966)
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Volume 13 (1965)
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Volume 12 (1964)
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Volume 11 (1963)
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Volume 10 (1962)
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Volume 9 (1961)
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Volume 8 (1960)
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Volume 7 (1959)
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Volume 6 (1958)
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Volume 5 (1957)
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Volume 4 (1956)
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Volume 3 (1955)
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Volume 2 (1954)
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Volume 1 (1953)