bluuebunny/crossref_metadata_2025_split huggingface dataset:
HOMOMORPHIC FILTERING — THEORY AND PRACTICE*
Authors: BUTTKUS B. 
Published: April 2006

AbstractThe application of homomorphic filtering in marine seismic reflection work is investigated with the aims to achieve the estimation of the basic wavelet, the wavelet deconvolution and the elimination of multiples. Each of these deconvolution problems can be subdivided into two parts: The first problem is the detection of those parts in the cepstrum which ought to be suppressed in processing. The second part includes the actual filtering process and the problem of minimizing the random noise which generally is enhanced during the homomorphic procedure.The application of homomorphic filters to synthetic seismograms and air‐gun measurements shows the possibilities for the practical application of the method as well as the critical parameters which determine the quality of the results. These parameters are:

the signal‐to‐noise ratio (SNR) of the input data
the window width and the cepstrum components for the separation of the individual parts
the time invariance of the signal in the trace.

In the presence of random noise the power cepstrum is most efficient for the detection of wavelet arrival times. For wavelet estimation, overlapping signals can be detected with the power cepstrum up to a SNR of three. In comparison with this, the detection of long period multiples is much more complicated. While the exact determination of the water reverberation arrival times can be realized with the power cepstrum up to a multiples‐to‐primaries ratio of three to five, the detection of the internal multiples is generally not possible, since for these multiples this threshold value of detectibility and arrival time determination is generally not realized.For wavelet estimation, comb filtering of the complex cepstrum is most valuable. The wavelet estimation gives no problems up to a SNR of ten. Even in the presence of larger noise a reasonable estimation can be obtained up to a SNR of five by filtering the phase spectrum during the computation of the complex cepstrum. In contrast to this, the successful application of the method for the multiple reduction is confined to a SNR of ten, since the filtering of the phase spectrum for noise reduction cannot be applied. Even if the threshold results are empirical, they show the limits fór the successful application of the method.
CONTRIBUTION A L'ETUDE DE L'EQUIVALENCE EN PROSPECTION ELECTRIQUE (COURANT CONTINU ET MAGNETOTELLURIQUE)*
Authors: ROCROI J. P. 
Published: April 2006

AbstractIn all electrical methods (EM, MT, DC), a theoretical one‐to‐one relation links the apparent resistivity diagram at a station with the local distribution of the resistivities in a tabular earth. Unfortunately, the actual field diagrams derive from a few measurements of limited accuracy and the one‐to‐one relation vanishes. Calculating the distribution of the earth resistivities from the field diagrams is thus an undetermined problem, which experience has shown to be partly controlled by approximate laws of “equivalence”. The use of these rough rules can produce only a very restricted number of the resistivity distributions that correspond to calculated diagrams which do not differ from a given field curve by more than a tolerable discrepancy. On the other hand, the full set of such “equivalent” solutions is given automatically by a computer program. Tests made on field examples prove that a few geological data generally reduce the wide range of undetermination.
RESULTS OF GRAVITY SURVEY OVER RANIGANJ COALFIELD, INDIA*
Authors: VERMA R. K. , MAJUMDAR R. , GHOSH DEBABRATA , GHOSH ASHISH , GUPTA N. C. 
Published: April 2006

AbstractResults of a gravity survey conducted over Raniganj coalfield, one of the Gondwana basins of Damodar Valley in north‐eastern part of India, are presented. The gravity field was separated into regional and residual components. The residual Bouguer anomaly map shows that the coalfield is characterized by a gravity low of about—32 mGal associated with Gondwana sediments. The deepest part of basin is found to be located near Asansole (23° 40’N, 86° 55’E), where the maximum thickness of sediments is estimated to be about 1.3 miles (2.08 km). The faults along the northern as well as the southern boundaries are found to be normal. The Gondwana sediments appear to continue eastward beneath alluvium and laterite of Bengal basin as far as 87° 25’E.
THE INDUCED POLARIZATION RESPONSE OF A THIN HIGHLY‐CONDUCTIVE ORE BODY*
Authors: FISHER M. E. , HURLEY D. G. 
Published: April 2006

AbstractConsider a lamina of ore of thickness 2t whose electrical resistivity p2 is much smaller than the resistivity p1 of the surrounding host rock. The induced polarization response of such an ore body is investigated under the assumption that it arises from the variation of p2 with the frequency of measurement.Let p2l and p2h be the resistivities of the ore‐body for the low and high frequencies of measurement and L a length of the order of the distance between the transmitting electrodes. A theory is developed under the assumptions that each of the quantities t/L, p2l/p1, p2h/p1, Lp2l/2tp1, and Lp2h/tp1 is small. The main conclusion is that the frequency effect parameter P is given approximately by P=cL(p2l − p2h)/2tp1, where the constant c is independent of t, p2l, p2h, and p1. Thus for a family of similar ore bodies having differing values of t, P will be the larger the smaller t.Detailed results are given for a semi‐infinite submerged dipping dyke and the two dimensional Wenner array.
FAST AUTOMATIC PROCESSING OF RESISTIVITY SOUNDINGS*
Authors: BICHARA M. , LAKSHMANAN J. 
Published: April 2006

AbstractThe difficulty to use master curves as well as classical techniques for the determination of layer distribution (ei, ρi) from a resistivity sounding arises when the presumed number of layers exceeds five or six.The principle of the method proposed here is based on the identification of the resistivity transform. This principle was recently underlined by many authors. The resistivity transform can be easily derived from the experimental data by the application of Ghosh's linear filter, and another method for deriving the filter coefficientes is suggested.For a given theoretical resistivity transform corresponding to a given distribution of layers (thicknesses and resistivities) various criteria that measure the difference between this theoretical resistivity transform and an experimental one derived by the application of Ghosh's filter are given. A discussion of these criteria from a physical as well as a mathematical point of view follows.The proposed method is then exposed; it is based on a gradient method. The type of gradient method used is defined and justified physically as well as with numerical examples of identified master curves. The practical use for the method and experimental confrontation of identified field curves with drill holes are given. The cost as well as memory occupation and time of execution of the program on CDC 7600 computer is estimated.
MINI‐SOSIE FOR LAND SEISMOLOGY*
Authors: BARBIER M. G. , BONDON P. , MELLINGER R. , VIALLIX J. R. 
Published: April 2006

AbstractMini‐sosie consists in using a vibration‐rammer as seismic source and changing the striking rate by varying the engine speed, resulting in a random impulse transmission. The recording instruments are made up of two seismic traces, two constant gain amplifiers and a two‐channel sosie processor which performs the decoding in real time by using the actual transmission times supplied by a captor located on top of the vibration‐rammer's plate. An idea of the possible penetration is given by the recording of a velocity survey. Other results obtained in seismic reflection and refraction are given.
A FAST FOURIER TRANSFORM METHOD FOR RAPID COMPUTATION OF GRAVITY AND MAGNETIC ANOMALIES DUE TO ARBITRARY BODIES*
Authors: BHATTACHARYYA B. K. , NAVOLIO M. E. 
Published: April 2006

AbstractThe spectrum of a magnetic or a gravity anomaly due to a body of a given shape with either homogeneous magnetization or uniform density distribution can be expressed as a product of the Fourier transforms of the source geometry and the Green's function. The transform of the source geometry for any irregularly‐shaped body can be accurately determined by representing the body as closely as possible by a number of prismatic bodies. The Green's function is not dependent upon the source geometry. So the analytical expression for its transform remains the same for all causative bodies. It is, therefore, not difficult to obtain the spectrum of an anomaly by multiplying the transform of the source geometry by that of the Green's function. Then the inverse of this spectrum, which yields the anomaly in the space domain, is calculated by using the Fast Fourier Transform algorithm. Many examples show the reliability and accuracy of the method for calculating potential field anomalies.
LONG PERIOD STATICS DETERMINATION BY INVERSE FILTERING*
Authors: KIRKHAM D. J. , POGGIAGLIOLMI E. 
Published: April 2006

AbstractThe relative time shift of CDP reflections, caused by long period statics, is treated as the result of a filtering process. The shape of the filter is that of a comb having the magnitude and spacing of its teeth determined by the CDP spread geometry. Convolution of a near surface anomaly with a comb filter representing the CDP spread geometry produces the same time fluctuations at CDP reflections (CDP statics) as the stacked traces across the anomaly. Conversely, the near surface time anomaly is given by the convolution of the CDP statics with the inverse of the comb filter. Provided that CDP statics can be separated from noise, dip, and residual normal moveout, it is pcissible to determine long period statics with a relative wavelength of between half a spreadlength and five spreadlengths.The object of this paper is to present the theory and practical applications of the method. Several examples based on synthetic and real data will also be discussed.
ON TRACING SEISMIC RAYS WITH SPECIFIED END POINTS IN LAYERS OF CONSTANT VELOCITY AND PLANE INTERFACES*
Authors: CHANDER R. 
Published: April 2006

AbstractA polygonal ray path connects the seismic source and detector positions when the intervening medium consists solely of constant velocity layers with plane interfaces which may have arbitrary orientation. The coordinates of the ray vertices satisfy a system of coupled equations resulting from the requirement that Fermat's principle be satisfied along the ray path. Solving the system of equations is equivalent to tracing the ray numerically. A notable feature of this approach is that a ray which is critically refracted over a segment of its path requires no special handling.
CHARACTERISTICS OF AUDIO AND SUB‐AUDIO TELLURIC SIGNALS*
Authors: TELFORD W. M. 
Published: April 2006

AbstractTelluric current measurements in the audio and sub‐audio frequency range, made in various parts of Canada and South America over the past four years, indicate that the signal amplitude is relatively uniform over 6–8 midday hours (LMT) except in Chile and that the signal anisotropy is reasonably constant in azimuth.
RESOLVING ANISOTROPY IN LAYERED MEDIA BY JOINT INVERSION*
Authors: JUPP D. L. B. , VOZOFF K. 
Published: April 2006

AbstractA finite number of layers must normally be used to represent the electrical properties of a horizontally‐layered region. It is well known that these representative layers must include anisotropy.Applying the concept of joint inversion to DC resistivity and magnetotelluric (electromagnetic) data from a structure consisting of many fine layers, we show how the resistivities in the horizontal and vertical directions can be separately determined in each layer. The results are related to the contrasts existing in the interbeds which comprise the composite layers.The method has applications in both engineering and exploration.
USE OF REMOTE SENSING FROM SPACE PLATFORMS FOR REGIONAL GEOLOGIC EVALUATION AND FOR PLANNING GROUND EXPLORATION*
Authors: CASSINIS R. 
Published: April 2006

AbstractThe advantages and limitations of remote sensing exploration from space platforms are outlined with special reference to the geologic objectives.The enhancement techniques of the multispectral imagery and their effects are illustrated in order to improve the interpretation of geologic linears and the discrimination of soils and rocks.Three cases of application are shown, dealing with different geologic regions.The ability of remote sensing from space to be employed in both regional and local problems is shown.The planning of exploration by airborne and ground geophysical methods can be substantially helped after the results of remote sensing, and large economic gains can be reached.
RESISTIVITY SOUNDING ON A MULTI‐LAYERED EARTH WITH TRANSITIONAL LAYERS. PART I: THEORY*
Authors: PATELLA D. 
Published: April 2006

AbstractThe electrical potential generated by a point source of current on the ground surface is studied for a multi‐layered earth formed by layers alternatively characterized by a constant conductivity value and by conductivity varying linearly with depth. The problem is accounted for by solving a Laplace's differential equation for the uniform layers and a Poisson's differential equation for the transitional layers. Then, by a simple algorithm and by the introduction of a suitable kernel function, the general expression of the apparent resistivity for a Schlumberger array placed on the surface is obtained. Moreover some details are given for the solution of particular cases as 1) the presence of a infinitely resistive basement, 2) the absence of any one or more uniform layers, and 3) the absence of any one or more transitional layers. The new theory proves to be rather general, as it includes that for uniform layers with sharp boundaries as a particular case. Some mathematical properties of the kernel function are studied in view of the application of a direct system of quantitative interpretation. Two steps are considered for the solution of the direct problem: (i) The determination of the kernel function from the field measurements of the apparent resistivity. Owing to the identical mathematical formalism of the old with this new resistivity theory, the procedures there developed for the execution of the first step are here as well applicable without any change. Thus, some graphical and numerical procedures, already published, are recalled. (ii) The determination of the layer distribution from the kernel function. A recurrent procedure is proposed and studied in detail. This recurrent procedure follows the principle of the reduction to a lower boundary plane, as originally suggested by Koefoed for the old geoelectrical theory. Here the method differs mainly for the presence of reduction coefficients, which must be calculated each time when passing to a reduced earth section.
A NOTE ON MAGNETIZED SPHERES*
Authors: RAO B. S. R. , RAO T. K. S. PRAKASA , MURTHY A. S. KRISHNA 
Published: April 2006

AbstractThe interpretation of total field anomalies becomes somewhat complicated, especially when an arbitrarily magnetized spherical ore mass happens to be the causative body. Even though some attempts have been made to analyze total field anomaly maps, they are often too complicated and their underlying assumptions in respect of permanent and induced components of magnetism are far from realistic. In this note, an attempt has been made to show that vertical magnetic anomalies are capable of yielding interpretation with ease and precision as far as magnetized spheres are concerned. An empirical method has been outlined for computing the magnetization inclination in the plane of the profile using the measured distances between principal maximum, principal minimum, and zero anomaly positions on a magnetic anomaly profile.
REFLECTIONS AND REFRACTIONS FROM CURVED INTERFACES: MODEL STUDY *
Authors: GUPTA S. K. 
Published: April 2006

AbstractReflections and refractions from curved interfaces were studied on two dimensional scale models. Time of arrival, amplitude and character of reflected, converted, and refracted waves were mainly used for this study. Some reflected refractions, refracted reflections and diffractions were also considered. It was possible to separate PS and SP waves and to study their amplitude and character separately. From the amplitude study of refracted arrivals it was concluded that the refracted ray path penetrates into the high velocity layer rather than propagating along the interface. Although most of the results are interesting from the theoretical point of view, a few applications to exploration problems are suggested.
SOME APPLICATIONS OF IP‐TECHNIQUE FOR DIFFERENT GEOPHYSICAL PROSPECTING PURPOSES *
Authors: MALMQVIST L. 
Published: April 2006

AbstractThe usefulness of IP‐technique for different geophysical purposes is discussed on the basis of field examples. IP and resistivity results are not always correlated, and the IP‐information may be unique in prospecting for very low grade sulphide mineralizations. The IP‐technique seems to be useful sometimes in prospecting for disseminated Ni‐Cu‐ mineralizations. A massive sulphide mineralization could be localized using IP.The disturbances from different kinds of geological objects other than prospecting targets generally are smaller in IP‐work than in resistivity work. It was possible to discriminate between apparent resistivity anomalies caused by shear zones and by sulphide mineralizations by means of IP‐measurements. The influence of magnetite on IP‐ measurements is briefly discussed. The relation between ground magnetic measurements ΔZ and the IP‐parameter is in many areas weak and does not seriously influence the interpretation of the IP‐measurements. A high correlation between ΔZ and IP‐measurements has been found on a titaniferous iron ore. This ore body gives strong IP‐anomalies indicating that it is a good IP‐target. Finally, the application of small moving arrays in very detailed IP‐measurements is found useful for detailed mapping of a mineralized zone under a thin overburden and for determination of the dip of mineralized zones.
GEOELEKTRISCHE SONDIERUNGEN IN GRADIENTMEDIEN UND ÄQUIVALENTEN SCHICHTSYSTEMEN *
Authors: RÖSLER R. , SCHALLAR M. 
Published: April 2006

AbstractAnalytical solutions exist for the potential of a Point Source in media with depth dependent conductivity of the form σ(z) =σ0(1 +αz)n.Of particular importance is the case of the linear gradient (n= 1). More general distributions of conductivity with depth can be approximated by equivalent sequences of homogeneous layers. Comparison between such approximations and the analytical solution for media with linear gradient of conductivity indicates that already a coarse step function yields a reasonably good approximation.
RESISTIVITY SOUNDING ON A MULTI‐LAYERED EARTH WITH TRANSITIONAL LAYERS. PART II: THEORETICAL AND FIELD EXAMPLES *
Authors: PATELLA D. 
Published: April 2006

AbstractThis final part of our study of the resistivity sounding method in the presence of transitional layers deals with the direct application of the theoretical developments, previously reported, to both theoretical and field examples. The former are used to explain in more detail all steps of the direct procedure of interpreting resistivity measurements, when transitional layers with different dispositions are present in the assumed earth section. An alternate sequence of uniform and transitional layers is at first considered, then the case of a random sequence of these layers, and finally a sequence of only transitional layers. Then we give some logical considerations about the best fields of application of the new interpretation theory, with particular reference to hydrogeological, geological‐ structural, and mining exploration problems. Representative field examples are finally presented and discussed in detail for each of the exploration fields above listed. The comparison of the geophysical models obtained with the old interpretative scheme and the new system shows the greater resolving power of the new theory, provided that preliminary geological considerations, and where existing–borehole evidence justify the use of the new approach.
CALCULATION OF VELOCITY FROM SEISMIC REFLECTION AMPLITUDE *
Authors: BOISSE S. 
Published: April 2006

AbstractIt is not possible to determine accurate geological velocities from seismic velocity analysis for thin layers or complex structural features, especially under an unconformity. Instead, we can approach the problem of interval velocity with seismic amplitudes analysis and compute the reflection coefficient along the unconformity surface.An error estimation has been made on a model to test the possibility of such a method and to choose the best parameters to be used. The method has been applied on an actual case: the computed interval velocities show good correlation with the values obtained by a sonic log.
QUASI‐STATIC ELECTROMAGNETIC FIELDS OF A HORIZONTAL ELECTRICAL DIPOLE ON THE SURFACE OF A POLARIZABLE HALF‐SPACE *
Authors: RATHOR B. S. 
Published: April 2006

AbstractThe expressions for quasi‐static electromagnetic fields of a horizontal electrical dipole placed on the surface of a polarizable half‐space have been derived for low and high values of induced polarization parameter and presented along with numerical results. It has been observed that the polarity of the mutual impedance function is negative for low values and positive for high values of the induced polarization parameter in the entire time domain, whereas the induced voltage function is positive for low values of induced polarization parameter and becomes negative for high values. In the case of low values of induced polarization parameter the transient electromagnetic field in the beginning increases with time, later on it starts to decay with time. The present study shows that the decay rate of electromagnetic field is highly dependent upon the induced polarization parameter. In the light of the present study the conductivity of the polarizable medium may be determined more accurately.
INVERSION OF GRAVITY PROFILES BY POLYNOMIAL METHOD *
Authors: BALDI P. , UNGUENDOLI M. 
Published: April 2006

AbstractThe inversion of a gravity profile associated with a twodimensional distribution of mass with constant difference in density is dealt with, in an initial approximation, by using a polynomial of appropriate degree. The method can be applied successfully, for example, to sedimentary basins.Some examples confirm the applicability of the method, which can be readily programmed on a computer.
CALCULATION OF SYNTHETIC REFLECTION SEISMOGRAMS IN THE FREQUENCY DOMAIN *
Authors: NIELSEN P. H. 
Published: April 2006

AbstractCalculation of reflection seismograms in the frequency domain makes it possible to treat absorption correctly, i.e. makes it possible to include dispersion (= causality) and frequency dependent reflection coefficients.In the paper it is shown how such a calculation can be done in a reasonably efficient manner.