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- Volume 12, Issue 3, 1964
Geophysical Prospecting - Volume 12, Issue 3, 1964
Volume 12, Issue 3, 1964
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AMELIORATION DU RAPPORT SIGNAL / BRUIT A L'AIDE DU FILTRAGE EN EVENTAIL*
Authors J. P. FAIL, G. GRAU and P. C. LAYOTTEAbstractCase 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.
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GENERALISATION DES OPERATEURS D'ANTI‐RESONANCE A UN NOMBRE QUELCONQUE DE REFLECTEURS*
By G. KUNETZABSTRACTIt is well known that the better part of the effect, on a seismic trace, of a near surface reflector can be eliminated by the application, on the said trace, of a linear operator of only 3 terms.
It will be shown that the effect of any number of such near‐surface reflectors can be eliminated, in the same way, with the aid of an operator of finite length and the means to construct these operators will be given.
In addition, the formulae used lead to an easy check of the fact that a seismic trace (completed by symmetry with respect to zero time) has to be an auto‐correlation function and allow the construction and the physical interpretation of a function whose autocorrelation gives the seismic trace made symmetrical.
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A METHOD OF QUANTITATIVE INTERPRETATION OF THE ELECTRICAL FIELDS OF INFINITELY LONG SINKS AND HORIZONTAL CIRCULAR CYLINDRICAL BODIES*
By SUDHIR JAINAbstractUsing 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.
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EINIGE ERGEBNISSE DER VIBRATORTECHNIK IN DER INGENIEURGEOPHYSIK*
By H. MILITZERABSTRACTAfter a short introduction on the principle of the vibratortechnique the results of its application to sheets of ice, concrete and road surfaces are discussed. The interpretation is based on the assumption that the excited waves correspond to bending of the plates. The experimental results are compared with the theoretical dispersion curves.
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ÜBER DIE DIMENSIONIERUNG UND DAS VERHALTEN VON REGELKREISEN IM SEISMISCHEN VERSTÄRKER*
Authors HELMUT WACHHOLZ and KARL WEISSENSTEINERAbstractThe purpose of the automatic gain control in seismic amplifiers is to balance the slow decrease of the signal in such a manner that its energy does not exceed the capacity of the recording system. At the same time the interesting seismic content of the signal has to be preserved as undistortedly as possible. At first, the technical data of AGC circuits are calculated. The characteristic curves of circuits with one, two, and three time constants are computed. In circuits with two and more time constants an oscillating of the AGC is possible. In order to guarantee aperiodic operation, the ratio of the time constants must not fall below a certain value. As long as these technical conditions are complied with, the free choice of the largest time constant remains open and can be accommodated to the geophysical conditions.
From the endeavour to balance the slow decrease of the signal as well as possible, an upper limit for the choice of the time constants can be derived. A lower limit is obtained from the condition that the seismic content of the signal has to be preserved. The determinant time constant should lie between the two limits and differ from them as much as possible.
Finally, the problem of the amplifier “squeezed” by energy pulses is touched.
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SUR LA REPONSE TRANSITOIRE DES FORMATIONS RESISTIVES*
By J. LOEBABSTRACTThis paper deals with transient response of resistive formations to pulse sources. Computation of solutions of equations such as:
(1)is linked to computation of solutions of equations such as:
(2)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
(3)At the interfaces, the distribution of incident energy between transmitted and reflected energy is related to the ratio of characteristic impedances, i.e.
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
(4)(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:
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.
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BOOK REVIEW
Book Review in This Article:
P. F. Shokin, Gravimetry (Apparatus and Methods for Measuring Gravity)
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Volume 17 (1969)
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Volume 15 (1967)
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Volume 14 (1966)
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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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